CN116402973A - Oblique photography model optimization method and system based on LOD reconstruction - Google Patents
Oblique photography model optimization method and system based on LOD reconstruction Download PDFInfo
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Abstract
The invention belongs to the field of GIS and three-dimensional models, and discloses a method and a system for optimizing an oblique photography model based on LOD reconstruction, wherein the method comprises the following steps: establishing oblique photography slice standards, wherein the slice standards comprise a slice origin and a plurality of LOD level tiles, and constructing a plurality of effect target levels through the slice standards; establishing a mapping relation between the original data and an oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with an index of the oblique photographing slice standard; re-performing triangular mesh cutting on the LOD level of the original data according to the corresponding level standard, re-mapping textures to grids to obtain a re-cut tile model, wherein the data of the highest LOD level after mapping is reference data; generating a tile model of a plurality of effect target levels based on the reference data, and synthesizing the tile model and the re-cut tile model into a pyramid tree; the method is favorable for realizing consistent updating of the oblique photography data, and solves the problems of data organization optimization and data lightweight loading of the oblique photography model.
Description
Technical Field
The invention belongs to the field of GIS and three-dimensional models, and particularly relates to an oblique photography model optimization method and system based on LOD reconstruction.
Background
With the development of smart cities, three-dimensional models become more and more a necessary data source for building smart cities. In particular, a novel mapping technology-oblique photography technology which is emerging in the mapping field in recent years enables the acquisition of a three-dimensional model to be more convenient and the application of the oblique photography model to be more and more extensive.
The oblique photography modeling software is generally provided with a pyramid structure after the model is built, and the oblique photography model produced by different software products is different in hierarchical structure and is mainly in tree structure forms such as quadtree, octree, KD tree and the like. The closer the distance is during model browsing, the more abundant the model details are displayed, but in order to improve the loading rate, 3-4 levels of data are often reserved, and the requirement of rapid loading of large-scale oblique photography cannot be met. The existing oblique photographing tree structure on the market has different LOD level effects of different software products due to the flexibility of different tree structures, and the data loading efficiency is greatly different.
At present, there are two main modes of model LOD processing: firstly, redundant layers are deleted directly, although the levels are fixed, the requirements of quick loading of small scenes can be met, but loading of large-scale data cannot be carried, so that the effect is difficult to achieve the optimal effect; the other mode is to use the highest level data, generate other levels of data except the highest level by thinning the triangular net, and has the advantages that the triangular net thinning proportion can be adjusted through multiple tests so as to achieve the optimal data loading effect, but the mode is single and has no thinning standard, and the subsequently updated oblique photographic model cannot be strictly matched with the existing model. In any mode, the processing effect depends on the quality of the original data and the experience of related personnel, a certain reference is lacking, and the process and batch processing of the data cannot be realized.
Disclosure of Invention
In order to solve the defects existing in the prior art, the invention aims to provide an oblique photography model optimization method and system based on LOD reconstruction, which set a construction standard of oblique photography multi-stage LOD light weight, divide a light weight target into a plurality of main layers, and formulate a light weight criterion and a target of each layer, thereby being beneficial to realizing consistent oblique photography data update and solving the problems of oblique photography model data organization optimization and data light weight loading.
The method is realized by the following technical scheme: an oblique photography model optimization method based on LOD reconstruction comprises the following steps:
establishing an oblique photographing slice standard; the slicing standard comprises a slicing origin, the sizes, the triangular face numbers, the scale and the geometric errors of a plurality of LOD level tiles; the LOD hierarchy is a multi-level tile form constructed by utilizing a pyramid form, and a plurality of effect target hierarchies are constructed by slicing standards;
establishing a mapping relation between the original data and an oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with an index of the oblique photographing slice standard;
obtaining a hierarchy standard corresponding to the original data according to the formed preliminary hierarchy corresponding relation; re-performing triangular mesh cutting on the LOD level of the mappable original data according to the corresponding level standard, and re-mapping the texture to the grid to obtain a re-cut tile model; setting the data of the highest LOD level after mapping as reference data;
generating an orthographic image with an elevation based on the reference data as a first effect target level of target data, obtaining the elevation according to interpolation of the reference data, and obtaining a first elevation model as a first tile model of the first effect target level;
extracting building contours based on the reference data, stretching the building contours into building shells according to the sampling heights, and generating building shell textures by utilizing a texture mapping technology; overlapping the generated building shell texture with a second elevation model to form a second tile model of a second effect target level;
performing point cloud resampling based on the reference data, and reconstructing a third tile model of the first LOD level in the third effect target level;
grid simplification is performed based on the reference data, and a fourth tile model of a second LOD level in the third effect target level is generated;
and synthesizing the first tile model, the second tile model, the third tile model, the fourth tile model and the re-cut tile model into a complete pyramid tree.
Preferably, the first effect target level has a preliminary city appearance, the second effect target level is capable of distinguishing building contours, the third effect target level has blurred ground features, and the fourth effect target level has clear ground features.
The system of the invention is realized by the following technical scheme: an oblique photography model optimization system based on LOD reconstruction comprises the following modules:
the slice standard making module is used for making oblique photography slice standards; the slicing standard comprises a slicing origin, the sizes, the triangular face numbers, the scale and the geometric errors of a plurality of LOD level tiles; the LOD hierarchy is a multi-level tile form constructed by utilizing a pyramid form, and a plurality of effect target hierarchies are constructed by slicing standards;
the mapping module is used for establishing a mapping relation between the original data and the oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with the index of the oblique photographing slice standard;
the cutting module is used for obtaining a hierarchy standard corresponding to the original data according to the formed preliminary hierarchy corresponding relation; re-performing triangular mesh cutting on the LOD level of the mappable original data according to the corresponding level standard, and re-mapping the texture to the grid to obtain a re-cut tile model; setting the data of the highest LOD level after mapping as reference data;
the first tile model acquisition module is used for generating an orthographic image with an elevation based on the reference data as a first effect target level of target data, obtaining the elevation according to the interpolation of the reference data, and obtaining a first elevation model as a first tile model of the first effect target level;
the second tile model acquisition module is used for extracting building contours based on the reference data, stretching the building contours into building shells according to the sampling heights, and generating building shell textures by utilizing a texture mapping technology; overlapping the generated building shell texture with a second elevation model to form a second tile model of a second effect target level;
the third tile model acquisition module is used for carrying out point cloud resampling based on the reference data and reconstructing a third tile model of the first LOD level in the third effect target level;
the fourth tile model acquisition module is used for carrying out grid simplification based on the reference data and generating a fourth tile model of a second LOD (LOD) level in the third effect target level;
the synthesis module synthesizes the first tile model, the second tile model, the third tile model, the fourth tile model and the re-cut tile model into a complete pyramid tree;
the first effect target level has a preliminary city appearance, the second effect target level can distinguish building outlines, the third effect target level has fuzzy ground feature, and the fourth effect target level has clear ground feature.
Compared with the prior art, the invention has the following advantages:
1. the invention sets a standard for the light weight specification of a multi-level LOD oblique photography model, divides a light weight target into a plurality of main layers, and provides a method and a flow for carrying out data processing and data light weight on each layer. The standardized oblique photography light-weight method can be applied to loading and rendering of the ultra-large-scale oblique photography data, has seamless visual effect experience, and can effectively support the oblique photography data version management and data updating.
2. The method combines various modes to realize the light weight of the oblique photography model, including extracting building contours to generate outline urban landscape, and proposes a coplanar-based sampling simplification algorithm to improve the tile simplification effect, thereby solving the problems of data organization optimization and data light weight loading of the oblique photography model.
Drawings
FIG. 1 is a flow chart of a method for optimization of a tilted photography model based on LOD reconstruction in an embodiment of the present invention;
FIG. 2 is a schematic diagram of tile boundary line matching in an embodiment of the present invention.
Detailed Description
According to the oblique photography model optimization method and system based on LOD reconstruction, the original data are processed into the target LOD level form by setting the standard multi-level LOD oblique photography model organization form, and the LOD of the original data is reconstructed, so that the data organization mode is optimized, the data loading efficiency is improved, and the realization of consistent oblique photography data updating is facilitated. The present invention will be further described with reference to the drawings and examples, but the embodiments of the present invention are not limited thereto.
Example 1
Referring to fig. 1, the oblique photography model optimization method based on LOD reconstruction in this embodiment adopts the technical means that: 1) And (3) formulating oblique photography slicing standards, including slicing origins, and sizes, triangular face numbers, scales and geometric errors of each LOD level tile. 2) And establishing a mapping relation between the original data and the standard oblique photographic slice, and constructing a target level according to the LOD level requirements. 3) Reconstructing the constructed target LOD hierarchy and the fine hierarchy model of the original data into a new oblique photography model tree structure. Specifically, the method mainly comprises the following steps:
s1, making an oblique photographing slice standard; the slicing criteria include a slicing origin, and dimensions, triangle count, scale, geometric errors of a plurality of LOD level tiles. Where the LOD hierarchy refers to a multi-level tile form constructed using a pyramid form, as shown in table 1, with an organization pattern of spatial quadtrees or octrees. The coordinate system selects the CGCS country 2000 coordinate system.
TABLE 1 oblique photography model LOD hierarchical criteria
The oblique photography slicing criteria shown in table 1 constructs a plurality of effect target levels, each effect target level comprising at least one LOD level. In the embodiment, the first effect target level is LOD 13-LOD 14, which has a preliminary city appearance and is represented by an orthographic image with elevation; the second effect target level is LOD 15-LOD 16, a certain building contour can be distinguished, and an orthographic image overlapping elevation is adopted to obtain a building contour with a certain building contour; the third effect target level is LOD 17-LOD 18, has slightly blurred ground feature, and is constructed by adopting a point cloud sampling and poisson reconstruction algorithm; the fourth effect target level is LOD 19-LOD 20, has clear ground feature characteristics, can clearly see the ground feature, and is converted by adopting a high-definition layer of original data.
S2, establishing a mapping relation between the original data and the oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with indexes such as tile size, image resolution and the like in an effect target level of the oblique photographing slice standard. Since the raw data is not necessarily organized in a standard form, the best matching mode is generally adopted, namely:
(1) Raw data of several distinct levels are chosen as comparison objects, typically at a high definition level and at successive levels. For example, the original data levels are LOD (m) -LOD (n), where LOD (n) is the highest definition and LOD (m) is not high definition.
(2) The levels LOD (m) -LOD (n) of the original data are analyzed, and if the lowest level LOD (m) is not high definition and the resolution is severely lower than the target standard, the lowest level LOD (m) is discarded.
(3) If the highest level LOD (n) is similar to the target LOD20 standard, the highest level LOD (n) is mapped to the highest level LOD20 of the oblique slice standard.
(4) Similarly, the intermediate levels between LOD (m) to LOD (n) (i.e., between the lowest level and the highest level) are matched. Wherein the similarity measure is determined by tile size and image resolution.
S3, obtaining a hierarchy standard corresponding to the original data according to the formed preliminary hierarchy corresponding relation; re-performing triangular mesh cutting on the LOD level of the mappable original data according to the corresponding level standard, and re-mapping the texture to the grid to obtain a re-cut tile model; and setting the data of the highest LOD level after mapping as reference data.
S4, generating an orthophoto with an elevation based on the reference data as a first effect target level of target data, namely LOD 13-LOD 14 levels; and obtaining an elevation according to the reference data interpolation, and obtaining a Mesh model (namely a first elevation model) based on the elevation grid as a tile model of the first effect target level.
S41, generating a plan view by using a tile-based axis alignment bounding box (Axis Aligned Bounding Box, AABB); and obtaining an orthographic image of the tile by a three-dimensional off-screen rendering technology, and taking the orthographic image as the texture of the plane graph. The three-dimensional off-screen rendering technology is to perform perspective projection on the model from the right above the model and perform three-dimensional rendering to obtain an image generated by rendering buffer data. Wherein the calculation formula of perspective projection is as follows:
w＝x n w canvas w tile
h＝y n h canvas h tile
wherein x is n ,y n Representing normalized device coordinates; w and h represent the width and height of the texture, respectively; d represents the current tile viewing height, n represents the camera near clipping face distance, l represents the viewing cone left clipping face distance, r represents the viewing cone right clipping face distanceFrom, t represents the distance between the cutting surfaces on the viewing cone, b represents the distance between the cutting surfaces under the viewing cone, and w canvas And h canvas Representing the width and height, w, of the screen texture, respectively tile And h tile Representing the width and height of the tile, respectively.
S42, interpolating and obtaining the elevation from the reference data by adopting a GeoMipmap technology, and forming a Mesh model based on an elevation grid, wherein the Mesh model is used as a tile model of a first effect target level, namely a tile model of LOD 13-LOD 14 levels.
The idea of the GeoMipmap technique is to divide a model into a fixed number of grids, and vertically intersection each grid point with reference data to obtain a highest position point which is considered as an elevation point of the position. Different LOD levels may set different numbers of trellis trees.
Since the model of the hierarchy does not require highly accurate elevation data, the triangle mesh of the hierarchy has low accuracy, and a resolution of 50m by 50m can be used.
S5, extracting building contours based on reference data, stretching the building contours into building shells according to sampling heights, and generating building shell textures by utilizing a texture mapping technology; the resulting architectural shell texture is overlaid with a finer elevation model (i.e., a second elevation model) to form a second effect target level tile model, i.e., a LOD 15-LOD 16 level tile model.
Wherein the finer elevation model is relative to LOD 13-LOD 14 of the first effect target level. The fineness of the elevation model is influenced by the grid precision, and the higher the grid precision is, the finer the elevation model is; the fine range is set by the user according to the actual requirement, and in the preferred embodiment, the grid accuracy of the elevation model of the second effect target level is set to 20 x 20m, so that the effect is good.
The core of the step is to extract the building outline and then stretch the building outline. And extracting the building outline according to a morphological algorithm, stretching the building outline into a building shell according to the sampling height, rendering the texture of the reference data to the building shell by using a texture mapping technology, and overlapping the building outline with a finer elevation model to form a tile model of LOD 15-LOD 16 level. The method comprises the following detailed steps:
s51, high-precision resampling is carried out on the elevation value of the tile model of the first effect target level, and the sampled precision is grid precision.
Since the second effect target level requires finer elevation, 20m x 20m resolution terrain may be used.
S52, calculating the elevation gradient, and enhancing the transformation of the elevation gradient. Elevation gradient refers to the rate of change of elevation z in both the x and y directions in a planar coordinate system, the greater the gradient change the more likely the building boundary line.
S53, extracting a building outline polygon; house boundaries are screened out by setting boundary line thresholds (i.e., change thresholds of elevation gradients).
In this embodiment, the maximum value of the first 10% is selected as the boundary threshold. Since the high-rise building contours are mostly regular, polygons which meet the threshold requirements of boundary lines, but have abnormal shapes and do not meet the requirements of the building contours are eliminated.
S54, stretching the extracted building outline polygon into a three-dimensional building model.
And S55, adopting an orthographic projection off-screen rendering technology to each building surface to obtain building textures, and attaching the building textures to the three-dimensional building model obtained by stretching in the step S54 to obtain the textured building model.
S56, generating an elevation tile model of a second effect target level (namely two levels of LOD 15-LOD 16) by adopting the technology in the step S4.
S57, fusing the building model generated in the step S55 into the elevation tile model generated in the step S56, and obtaining the tile model of the second effect target level.
In this embodiment, the grid corresponding to the building outline polygon in the elevation tile model is removed, and the textured building model is combined with the elevation tile model, so that the high-rise building can be seen in the common elevation tile model.
S6, performing point cloud resampling based on the reference data, and reconstructing a tile model of an LOD17 level in the third effect target level by using a Poisson reconstruction mode.
The grid accuracy of the hierarchical tile model is finer than that of the LOD16 hierarchy, the tile range is smaller, and low-rise buildings and roadside trees can be seen. The core content of the step comprises the following steps:
s61, sampling point cloud: the core principle of the point cloud sampling is to place sampling points on the graphic element randomly or according to a certain strategy to obtain a point cloud model.
S62, reconstructing poisson: the core of poisson reconstruction is to construct discrete points into a continuous triangular network through calculation, so as to obtain a reconstructed third tile model. The specific flow involves the processes of constructing octree, setting function space, calculating vector field, solving poisson equation, extracting isosurface, constructing triangle net, etc.
This step can be accomplished by the open source software MeshLab; the MeshLab software is mainly used for processing and unstructured editing of the 3D triangle mesh, is suitable for a Windows, macOSX, linux system, and is provided with a program package for mesh poisson reconstruction and encapsulation.
S63, texture reprojection: and re-performing texture mapping on the poisson reconstructed model based on the material of the reference data to obtain clear textures.
S64, cutting a bounding box: the bottom surface of the triangle mesh obtained after poisson reconstruction is square, but the shape of the bottom surface of the actual oblique photography model is mostly not regular, so that the triangle mesh needs to be re-cut according to the bounding box range in the step S4.
S7, grid simplification is carried out based on the reference data, and a tile model of an LOD18 level in the third effect target level is generated, so that finer ground objects can be seen.
The grid accuracy of the hierarchical tile model is finer than that of the LOD17 hierarchy, and the tile texture is clearer with a larger number of tiles. Because the number of tiles of the reference data is large, adjacent tiles are combined by adopting a tile boundary combining algorithm, and then grid simplification is carried out to avoid the problems that the boundary is broken or the boundary is difficult to simplify.
In this embodiment, the model of each level is composed of grids, and only the grid generation modes of different LOD levels are different. The higher the LOD level, the more the number of grids, the finer the model, since the number of single-tile grids before the LOD18 level is less than 3000, the need for refinement of the model is not very high, even if there are gaps, but to the LOD18 level, as the viewing height is lowered, the human eye can see more tile details, gaps between tiles affect visual effects in addition to the effect of grid simplification, so that the LOD18 level needs to perform gap merging on the tiles.
The method specifically comprises the following steps:
s71, performing gap combination on the tiles through a tile boundary combination algorithm. The method comprises the following specific steps:
1) Extracting boundary triangles of tiles to be combined to obtain tile boundary lines;
2) The tile boundary lines are topologically related, and segments of the tile boundary lines are formed and ordered.
3) And sequentially matching the boundary line of the first tile A with the boundary line of the second tile B, namely judging whether the boundary lines of the two tiles are adjacent or not, as shown in fig. 2.
4) And fusing the matched boundary lines, including adjacent point merging, separated point projection and other technologies.
5) Reconstructing the tile boundary surface based on the fused boundary line.
6) And de-duplicating the reconstructed tile vertexes to obtain the merged tile boundaries.
S72, a grid simplification algorithm is cycled for a plurality of times, and reference data is simplified, wherein the reference data comprises conventional algorithm flows such as point collapse, boundary collapse and the like; and simultaneously, a coplanar-based sampling simplification algorithm is provided, and the triangular network of the building and the ground is fused.
1) Removing folding surfaces and repeating surfaces, and grouping triangular surfaces according to the normal vector and connectivity of each triangular surface to form different surface blocks;
2) And separating the building surface and the ground according to the statistical characteristics of the surface blocks. The statistical features include plane normal, height information, and patch size.
3) Thinning the vertex of the identified ground triangular surface and generating a Delaunay triangular network.
4) And calculating a peripheral outline of the identified building triangular surface, and regenerating a triangular network based on a polygonal triangulation algorithm.
5) And fusing the building with the triangular network on the ground to generate a new simplified model.
S8, combining the generated tile models of the LOD 13-LOD 18 levels and the tile model re-cut in the step S3 into a complete pyramid tree, and setting the geometric error of each LOD level and the tile association relation between the levels.
S9, when part of oblique photography needs to be updated, firstly, cutting the oblique photography data (such as LOD19 and LOD 20) which need to be updated again according to the tile standard (including the slice origin and the tile size) so as to replace the existing tiles with the same size and the same level. Tiles of low-precision LODs (LOD 13-LOD 18) need to be recombined with the original oblique photographic data and replaced with the existing corresponding tile models. The range of original oblique photography tiles that need to be obtained is:
example 2
Based on the same inventive concept as embodiment 1, this embodiment provides an oblique photography model optimization system based on LOD reconstruction, including the following modules:
the slice standard making module is used for making oblique photography slice standards; the slicing standard comprises a slicing origin, the sizes, the triangular face numbers, the scale and the geometric errors of a plurality of LOD level tiles; the LOD hierarchy is a multi-level tile form constructed by utilizing a pyramid form, and a plurality of effect target hierarchies are constructed by slicing standards;
the mapping module is used for establishing a mapping relation between the original data and the oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with the index of the oblique photographing slice standard;
the cutting module is used for obtaining a hierarchy standard corresponding to the original data according to the formed preliminary hierarchy corresponding relation; re-performing triangular mesh cutting on the LOD level of the mappable original data according to the corresponding level standard, and re-mapping the texture to the grid to obtain a re-cut tile model; setting the data of the highest LOD level after mapping as reference data;
the first tile model acquisition module is used for generating an orthographic image with an elevation based on the reference data as a first effect target level of target data, obtaining the elevation according to the interpolation of the reference data, and obtaining a first elevation model as a first tile model of the first effect target level;
the second tile model acquisition module is used for extracting building contours based on the reference data, stretching the building contours into building shells according to the sampling heights, and generating building shell textures by utilizing a texture mapping technology; overlapping the generated building shell texture with a second elevation model to form a second tile model of a second effect target level;
the third tile model acquisition module is used for carrying out point cloud resampling based on the reference data and reconstructing a third tile model of the first LOD level in the third effect target level;
the fourth tile model acquisition module is used for carrying out grid simplification based on the reference data and generating a fourth tile model of a second LOD (LOD) level in the third effect target level;
the synthesis module synthesizes the first tile model, the second tile model, the third tile model, the fourth tile model and the re-cut tile model into a complete pyramid tree;
the first effect target level has a preliminary city appearance, the second effect target level can distinguish building outlines, the third effect target level has fuzzy ground feature, and the fourth effect target level has clear ground feature.
The above modules in this embodiment are used to execute the steps in embodiment 1, and the detailed execution process thereof is referred to embodiment 1 and is not repeated herein.
The foregoing is only illustrative of the preferred embodiments of the present invention, but the scope of the invention is not limited thereto, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principles of the present invention should be made therein and are intended to be equivalent substitutes.
Claims (10)
1. The oblique photography model optimization method based on LOD reconstruction is characterized by comprising the following steps of:
establishing an oblique photographing slice standard; the slicing standard comprises a slicing origin, the sizes, the triangular face numbers, the scale and the geometric errors of a plurality of LOD level tiles; the LOD hierarchy is a multi-level tile form constructed by utilizing a pyramid form, and a plurality of effect target hierarchies are constructed by slicing standards;
establishing a mapping relation between the original data and an oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with an index of the oblique photographing slice standard;
obtaining a hierarchy standard corresponding to the original data according to the formed preliminary hierarchy corresponding relation; re-performing triangular mesh cutting on the LOD level of the mappable original data according to the corresponding level standard, and re-mapping the texture to the grid to obtain a re-cut tile model; setting the data of the highest LOD level after mapping as reference data;
generating an orthographic image with an elevation based on the reference data as a first effect target level of target data, obtaining the elevation according to interpolation of the reference data, and obtaining a first elevation model as a first tile model of the first effect target level;
extracting building contours based on the reference data, stretching the building contours into building shells according to the sampling heights, and generating building shell textures by utilizing a texture mapping technology; overlapping the generated building shell texture with a second elevation model to form a second tile model of a second effect target level;
performing point cloud resampling based on the reference data, and reconstructing a third tile model of the first LOD level in the third effect target level;
grid simplification is performed based on the reference data, and a fourth tile model of a second LOD level in the third effect target level is generated;
and synthesizing the first tile model, the second tile model, the third tile model, the fourth tile model and the re-cut tile model into a complete pyramid tree.
2. The method of claim 1, wherein the first effect target level has a preliminary city appearance, the second effect target level is capable of distinguishing building contours, the third effect target level has blurred terrain features, and the fourth effect target level has sharp terrain features.
3. The method of claim 1, wherein establishing a mapping relationship between the raw data and the oblique photography slicing criteria, and forming a preliminary hierarchical correspondence by comparing the raw data with an index of the oblique photography slicing criteria, comprises:
selecting a plurality of clear-level original data as comparison objects;
analyzing the layers LOD (m) -LOD (n) of the original data, and discarding the lowest layer LOD (m) if the lowest layer LOD (m) is not high definition and the resolution is seriously lower than the target standard;
if the highest level LOD (n) is similar to the target LOD20 standard, mapping the highest level LOD (n) to be the highest level of the oblique photography slice standard;
the intermediate levels between LOD (m) to LOD (n) are matched.
4. The method of claim 1, wherein generating an orthographic image with an elevation as a first effect target level of target data based on reference data, interpolating the elevation from the reference data, obtaining a first elevation model as a first tile model of the first effect target level, comprises:
generating a plan view based on the tile's axis alignment bounding box; obtaining an orthographic image of the tile through an off-screen rendering technology, and taking the orthographic image as a texture of the plan;
and interpolating the reference data to obtain an elevation, and forming a Mesh model based on an elevation grid as a first tile model of a first effect target level.
5. The method of claim 4, wherein the off-screen rendering technique is a three-dimensional off-screen rendering technique, wherein perspective projection is performed on the model from directly above the model and three-dimensional rendering is performed, and an image generated by rendering the buffered data is obtained.
6. The method of claim 5, wherein the perspective projection is calculated as:
w＝x n w canvas w tile
h＝y n h canvas h tile
wherein x is n ,y n Representing normalized device coordinates; w and h represent the width and height of the texture, respectively; d represents the current tile viewing height, n represents the camera near clipping surface distance, l represents the viewing cone left clipping surface distance, r represents the viewing cone right clipping surface distance, t represents the viewing cone upper clipping surface distance, b represents the viewing cone lower clipping surface distance, w canvas And h canvas Representing the width and height, w, of the screen texture, respectively tile And h tile Representing the width and height of the tile, respectively.
7. The method of claim 1, wherein the building contours are extracted based on reference data, stretched into building shells according to the sampled heights, and texture mapping techniques are utilized to generate building shell textures; overlapping the generated building envelope texture with a second elevation model to form a second tile model of a second effect target level, comprising:
resampling the elevation value of the first tile model of the first effect target level, wherein the sampled precision is grid precision;
calculating the elevation gradient, and enhancing the transformation of the elevation gradient;
extracting a building outline polygon; screening house boundaries by setting a change threshold value of the elevation gradient;
stretching the extracted building outline polygon into a three-dimensional building model;
each building surface is subjected to orthographic projection off-screen rendering technology to obtain building textures, and the building textures are attached to the stretched three-dimensional building model to obtain a textured building model;
generating an elevation tile model of a second effect target level;
and fusing the textured building model into the generated elevation tile model to obtain a second tile model of a second effect target level.
8. The method of claim 1, wherein reconstructing a third tile model of the first LOD level of the third effect target level using poisson reconstruction based on the point cloud resampling of the reference data comprises:
sampling point cloud to obtain a point cloud model;
poisson reconstruction, constructing discrete points into a continuous triangular net through calculation, and obtaining a reconstructed third tile model;
re-projecting the texture, and re-performing texture mapping on the texture of the third tile model based on the reference data after poisson reconstruction to obtain clear texture;
and (5) re-cutting the triangular net obtained after poisson reconstruction.
9. The method of claim 1, wherein the mesh reduction based on the reference data generates a fourth tile model of a second LOD level of the third effect target level, comprising:
and carrying out gap combination on the tiles through a tile boundary combination algorithm: extracting boundary triangles of tiles to be combined to obtain tile boundary lines; performing topological association on the tile boundary lines to form a plurality of segments of the tile boundary lines and sequencing; sequentially matching the boundary line of the first tile with the boundary line of the second tile; fusing the matched tile boundary lines; reconstructing a tile boundary surface based on the fused boundary line; de-duplicating the reconstructed tile vertexes;
a repeated cyclic grid simplifying algorithm is adopted to simplify the reference data; and fusing the triangular network of the building and the ground through a coplanar sampling simplification algorithm.
10. An oblique photography model optimization system based on LOD reconstruction is characterized by comprising the following modules:
the slice standard making module is used for making oblique photography slice standards; the slicing standard comprises a slicing origin, the sizes, the triangular face numbers, the scale and the geometric errors of a plurality of LOD level tiles; the LOD hierarchy is a multi-level tile form constructed by utilizing a pyramid form, and a plurality of effect target hierarchies are constructed by slicing standards;
the mapping module is used for establishing a mapping relation between the original data and the oblique photographing slice standard, and forming a preliminary level corresponding relation by comparing the original data with the index of the oblique photographing slice standard;
the cutting module is used for obtaining a hierarchy standard corresponding to the original data according to the formed preliminary hierarchy corresponding relation; re-performing triangular mesh cutting on the LOD level of the mappable original data according to the corresponding level standard, and re-mapping the texture to the grid to obtain a re-cut tile model; setting the data of the highest LOD level after mapping as reference data;
the first tile model acquisition module is used for generating an orthographic image with an elevation based on the reference data as a first effect target level of target data, obtaining the elevation according to the interpolation of the reference data, and obtaining a first elevation model as a first tile model of the first effect target level;
the second tile model acquisition module is used for extracting building contours based on the reference data, stretching the building contours into building shells according to the sampling heights, and generating building shell textures by utilizing a texture mapping technology; overlapping the generated building shell texture with a second elevation model to form a second tile model of a second effect target level;
the third tile model acquisition module is used for carrying out point cloud resampling based on the reference data and reconstructing a third tile model of the first LOD level in the third effect target level;
the fourth tile model acquisition module is used for carrying out grid simplification based on the reference data and generating a fourth tile model of a second LOD (LOD) level in the third effect target level;
the synthesis module synthesizes the first tile model, the second tile model, the third tile model, the fourth tile model and the re-cut tile model into a complete pyramid tree;
the first effect target level has a preliminary city appearance, the second effect target level can distinguish building outlines, the third effect target level has fuzzy ground feature, and the fourth effect target level has clear ground feature.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116664581A (en) * | 2023-08-02 | 2023-08-29 | 山东翰林科技有限公司 | Oblique photography model quality verification and optimization method |
| CN117994464A (en) * | 2024-04-07 | 2024-05-07 | 中国海洋大学 | Method for constructing three-dimensional micro-geomorphic model by processing profile sonar point cloud data |
| CN118113394A (en) * | 2023-12-29 | 2024-05-31 | 湖北省数字产业发展集团有限公司 | Method and device for loading large-scale oblique photographic data |
| CN118212367A (en) * | 2024-05-22 | 2024-06-18 | 四川视慧智图空间信息技术有限公司 | Data top layer reconstruction method and device and electronic equipment |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116664581A (en) * | 2023-08-02 | 2023-08-29 | 山东翰林科技有限公司 | Oblique photography model quality verification and optimization method |
| CN116664581B (en) * | 2023-08-02 | 2023-11-10 | 山东翰林科技有限公司 | Oblique photography model quality verification and optimization method |
| CN118113394A (en) * | 2023-12-29 | 2024-05-31 | 湖北省数字产业发展集团有限公司 | Method and device for loading large-scale oblique photographic data |
| CN117994464A (en) * | 2024-04-07 | 2024-05-07 | 中国海洋大学 | Method for constructing three-dimensional micro-geomorphic model by processing profile sonar point cloud data |
| CN118212367A (en) * | 2024-05-22 | 2024-06-18 | 四川视慧智图空间信息技术有限公司 | Data top layer reconstruction method and device and electronic equipment |
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