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README.md

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License: MIT

libOL version 1.82

Quick and easy spatial localization with octree

Overview

the libOL 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

Build

Prerequisites for Linux or macOS

  • Install CMake
  • A valid C99 compiler
  • Open a shell window

Prerequisites for Windows

  • You first need to install CMake. 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 free Visual Studio Community 2019
  • Open the x64 Native Tools Command Prompt for VS (or x86 if you need to build a 32-bit version)

Build commands for all platforms

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

Optional steps

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

  • you need to install the libMeshb from GitHub
  • manually download files from the Git LFS repository: sample files
  • move them into /opt/libOL/sample_meshes/
  • uncompress them with xz -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.

Usage

It is made of a single ANSI 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 on Linux, macOS, and Windows 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 point
   printf("The closest triangle from (%g %g %g) is: %d, distance = %g\n",
          crd[0], crd[1], crd[2], TriIdx, dis);

   // Free the octree
   LolFreeOctree(OctIdx);