README.rst
1GeoHashTree for Point Cloud Data
2================================
3
4A file format and library for storing and rapidly accessing point cloud data, in particular LIDAR data.
5
6GeoHashTree organizes points into a tree structure for fast spatial access. The tree structure itself encodes the significant bits of at each node, so child nodes can omit them. The result is a smaller file than if all the points were stored with full precision. Each node includes statistical information about the children below (e.g. average/median Z value) permitting fast overview generation. Additional attributes are attached to the tree at parent nodes, below which all children share the attribute value. This reduces duplicate data storage further.
7
8The advantage of a GeoHashTree file over a LAS file is fast access and filtering, since the tree encodes useful information at each node to speed searches over the full set of points in the file. LASZ zipped files can be smaller, but will be less efficient at overviews, searching and sub-setting. GHT is a good working format for applications that will be filtering and querying large sets of LIDAR data.
9
10Requires
11========
12
13- `LibXML2 <http://www.xmlsoft.org/downloads.html>`_ for handling schema documents
14- `CUnit <http://cunit.sourceforge.net/>`_ for running unit tests
15- `CMake <http://www.cmake.org/cmake/resources/software.html>`_ to build
16
17Build
18=====
19
20CMake prefers builds "out of source", where all the generated files are created separately from the source directory. To make this happen, create a build directory, enter it, then invoke `cmake` with the source directory as the target argument.
21
22UNIX
23----
24
25::
26
27 mkdir libght-build
28 cd libght-build
29 cmake ../libght-src
30 make
31 make test
32 make install
33
34Windows
35-------
36
37::
38
39 mkdir libght-build
40 cd libght-build
41 cmake -G "NMake Makefiles" ..\libght-src
42 nmake
43 nmake install
44
45To Do
46=====
47
48- Opaque types in common header to separate user-API from internal API
49- Filtering functions to return sub-trees based on attribute or spatial constraints
50- Attribute statistics stored at top of tree
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52