shapelib

Searching the quadtree is a multi-stage process designed to balance speed and accuracy. The SHPTreeFindLikelyShapes() function in shptree.c implements the first stage.

1. Phase 1: Quadtree Traversal: The algorithm traverses the quadtree and collects shapeids from every node whose bounding rectangle overlaps the search rectangle. This stage is fast but can produce "false positives" because a shape's actual bounding box is often much smaller than its containing quadtree node.
2. Phase 2: Shape Verification: The actual shapes are fetched, and their specific bounding boxes are checked against the search area to filter out the false positives from Phase 1.
3. Phase 3 (Optional/Manual): A third phase can be implemented to verify if actual line segments within a shape cross the area of interest, though this is typically handled by drawing engines via clipping.

To build the Shapelib distribution using Microsoft Visual C++:

1. Navigate to the shapelib subdirectory within the unpacked distribution.
2. Open a DOS/Command Prompt window.
3. Run the following command:

nmake -f makefile.vc

Alternatively, you can create a manual Visual C++ project by including the following source files and building them as a Win32 console application:

• shpopen.c
• shptree.c
• shpdumptree.c

When building on MinGW or MSYS platforms, the procedure is identical to Unix/Linux, but you should specify the appropriate generator using the -G flag. Instead of "Unix Makefiles", use "MSYS Makefiles" to ensure compatibility with the platform.

cmake \
-S /path/to/shapelib-1.6.0 \
-B build_dir \
-G "MSYS Makefiles" \
-DCMAKE_INSTALL_PREFIX=/path/to/install \
-DEG_DATA=/path/to/eg_data/

To build shapelib on a Unix-like system, follow these steps in order:

1. Generate build scripts by running ./configure.
   • You can run ./configure --help to see available fine-tuning options.
2. Compile the project by running make.
3. (Optional) Run self-tests using make check.
4. Install the project using make install.

To build shapelib on Windows using the Visual C++ compiler:

1. Ensure you have run VCVARS32.BAT to set up your environment.
2. Open a command window and run nmake /f makefile.vc to build the code and executables.

Alternatively, you can manually create your own VC++ project using the source files.

The following CMake flags are used during the configuration step to control the build environment and test coverage.

-S <dir>             Path to the shapelib source tree
-B <dir>             Path to the build directory (out-of-source build)
-G <generator>       The build system generator (e.g., "Unix Makefiles" or "MSYS Makefiles")
-DCMAKE_INSTALL_PREFIX=<path>  The destination directory for the installation
-DEG_DATA=<path>     Path to the eg_data tree (required for "stream1" tests)