TdhGIS is a free GIS software application for Linux and Windows operating systems for spatial analysis of vector based geographic data. The software can also be used as a shapefile viewer and editor. Tim Hirrel is the developer of TdhGIS which was developed using C++, wxWidgets and SQLite. Hirrel, water resources engineer, developed the software based on functionality a from hydraulic network analysis program, TdhNet, and a vector graphics editing program, TdhCad. TdhGIS has 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 performs the following functions:
- Color polygons based on user data values using either Discrete intervals or Gradients.
- Allocate point data to user specified BUFFERS for points, polygons and multilines (e.g. find all gas stations within 1 mile of a highway).
- Allocates point data to polygons. (e.g. assigning structures to hydrological basins).
- Allocates polygon data to other polygons. (e.g. allocating population data by census block to political boundaries).
- Creates thiessen polygons (e.g. for all hospitals within a state, define the areas where a particular hospital is closer than any other).
- Created data contours (e.g. create lines of equal ground elevation based on a set of elevation points).
- Creates contour polygons (e.g. define the area where average rainfall exceeds a selected value based on weather station data).
The freeware can read and write shapefile and CSV format data.
For complete information, please visit the TdhGIS.com website and download the software and user’s manual. The user’s manual can now be downloaded separately from the programs, under the TdhGIS_Library link at TdhGIS.com.