TdhGIS

TdhGIS provides a set of vector based spatial analysis functions in executable programs for both the MS Windows and Linux operating systems. Current versions of TdhGIS are free of charge. User documentation is provided in a PDF file.
TdhGIS was developed using C++, wxWidgets and SQLite by Tim Hirrel, a water resources engineer with a background in application programming. Borrowing basic functionality from a hydraulic network analysis program, TdhNet, and a vector graphics editing program, TdhCad, TdhGIS adds vector spatial analysis useful for a wide variety of scientific applications.
Analysis Tools
TdhGIS has the ability to generate spatial data, including:
* Thiessen (Voronoi) Polygons - define the area closest to a given point within a set of points. Among the potential uses, thiessen polygons can be used to allocate data to points based on proximity.
* Contour Lines - define where interpolated data values are equal to the contour value.
* Contour Polygons - define the area above or below a selected contour value.
* Intersect Polygons - a set of polygons based on the vector intersection of 2 input sets of polygons. Handles many special cases such as concurrent points and lines.
* Merge Polygons - a set of polygons based the vector merging of 2 input sets of polygons.
* Subtract Polygons - a set of polygons based on the vector subtraction of one set of polygons from another.
* Exclusion polygons (i.e. holes) are generated and handled as appropriate within all spatial operations.
* Allocate Point Data to Polygons - data belonging to a set of points is allocated to a set of polygons based on which polygon contains each point (example: assign structure data to fire districts).
* Allocate Polygon Data to Polygons - data belonging to one set of polygons is allocated to another set of polygons (example: allocate population by census block to political boundaries).
Other Functionality
TdhGIS may interact with many other applications because of an open database structure and the ability to import and export common file formats, including shapefiles, comma separated variable (CSV) files and common graphic formats. TdhGIS provides basic data editing capabilities and the ability to manipulate the display of different data sets.

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