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Quick and easy spatial localization withoctree

thelibOL first store a mesh made of vertices, edges and triangles in an octree structure with a very small memory footprint.Subsequently, you can perform geometrical queries very quickly on this mesh:

• retrieve the closest entity from a given set of coordinates
• build the list of mesh entities than are include in a given bounding box
• project a vertex on any kind of geometrical entity
• launch a ray and get the first intersected entity
• all query operations can be performed in parallel as the library is thread safe

• InstallCMake
• A valid C99 compiler
• Open a shell window

• You first need to installCMake. Do not forget to choose "add cmake to the path for all users", from the install panel.
• Then you need a valid C compiler like the freeVisual Studio Community 2019
• Open the x64 Native Tools Command Prompt for VS (or x86 if you need to build a 32-bit version)

• unarchive the ZIP file
• cd libOL-master
• mkdir build
• cd build
• cmake ..
• cmake --build . --target install

Optionally, you may download some sample meshes to run the examples:

• you need to install thelibMeshb from GitHub
• manually download files from theGit LFS repository:sample files
• move them into /opt/libOL/sample_meshes/
• uncompress them withxz -d *.meshb.xz
• you may now enter /opt/libOL/examples directory and run the various examples

When speed is is more critical than memory, you can compile the library with the-DWITH_FAST_MODE option in order to speed-up queries by 35%, at the cost of 2.5 times the memory footprint.

It is made of a singleANSI C file and a header file to be compiled and linked alongside the calling program.
It may be used in C or C++ programs.Tested onLinux,macOS, andWindows 7->10.

Here is a basic example that builds an octree from a surface mesh made of vertices (NmbVer vertices stored in VerTab[]) and triangles (NmbTri elements stored in TriTab[]), then searches for the closest triangle from a set of coordinates:

int64_t OctIdx;int     TriIdx;double  dis, crd[3] = {0.2,2.5, -3.1 };// Build an octree from a surface mesh   OctIdx = LolNewOctree(  NmbVer, VerTab[1], VerTab[2],0,NULL,NULL,                           NmbTri, TriTab[1], TriTab[2],0,NULL,NULL,0,NULL,NULL,0,NULL,NULL,0,NULL,NULL,0,NULL,NULL,1,1);// Find the closest triangle from a given point   TriIdx = LolGetNearest(OctIdx, LolTypTri, crd, &dis,0.,NULL,NULL,0);// Print the triangle's index and the distance from the source pointprintf("The closest triangle from (%g %g %g) is: %d, distance = %g\n",          crd[0], crd[1], crd[2], TriIdx, dis);// Free the octreeLolFreeOctree(OctIdx);