Knowledge Base



KB10895 - Coordinate system support in TatukGIS products.

GIS software must understand the coordinate system of each layer to correctly rotate, scale, present distances, calculate measurements, and display layers in different coordinate systems together as a single map. TatukGIS state-of-the-art support for coordinate systems is user friendly and sufficiently powerful and flexible to satisfy advanced requirements of expert users. The software automatically recognizes thousands of coordinate systems for every supported vector and raster (image, grid) layer format and efficiently reprojects all layers (even huge images) on-the-fly between coordinate systems.

Because TatukGIS software automatically reads the coordinate system information of each layer and intelligently anticipates coordinate system settings, most common situations do not even require the user to select or edit the coordinate system information.

  • A map project or single layer with recognized coordinate system is opened. The software automatically reads the coordinate system and correctly displays the project or layer in accordance with the coordinate system.
  • A map project or single layer is already open when a layer with a different coordinate system is opened. The software automatically reads the coordinate system of the new layer and on-the-fly reprojects the layer display to the coordinate system of the already open project or layer.
  • A map project or single layer is already open when a new (empty) layer is created and opened (such as using the TatukGIS Editor Layer/New feature). The default settings automatically apply the coordinate system of the already open project or layer as the coordinate system of the new layer.
  • A map project or single layer is already open when a layer without a recognized coordinate system (because the coordinate system information is missing, corrupted, or the layer does not reflect a coordinate system) is opened, and the user selects the rectify layer option (in the Editor) to rectify and/or georeference the layer to a coordinate system. The default settings automatically apply the coordinate system of the already open project or layer to the rectification job.
  • A layer without a recognized coordinate system is opened and the user selects the rectify layer option (in the Editor) and selects the use reference layer coordinate system option. The default settings automatically apply the coordinate system of the reference layer to the rectification job.
  • Export a vector layer to a new file (such as using the Editor Layer/Export feature). The default settings generate the export to the same coordinate system as the source layer.
  • Export to an image file (such as using the Editor File/Export to image feature). The export is generated to the same coordinate system as the current map area display.

The user is required to perform a coordinate system selection only in situations when it is impossible for the software to anticipate the coordinate system.

  • Change the map area display (can involve a single layer or a multi-layer project) to a different coordinate system. The user must specify the map area coordinate system. (Refer to Editor/Viewer menu item File/Coordinate systems... help topic).
  • Export a vector layer to new file in a coordinate system that is different than the source layer. The user must specify the export coordinate system. (Refer to Editor menu item Layer/Export help topic.)
  • An opened map layer reflects a coordinate system that is known to the user, but the software is unable to read the coordinate system (because information is missing or corrupted). An (advanced) user may manually edit or apply the layer coordinate system information in the layer properties. (Refer to Editor/Viewer menu item Layer/Properties help topic.)
  • A layer without a recognized coordinate system is opened and the user wishes to rectify and/or georeference the layer to a coordinate system other than the coordinate system of an already opened project or layer or the coordinate system of a reference layer. The user must specify the coordinate system for the rectification job. (Refer to the coordinate system settings in the Editor Rectification options dialog box.)

In the situations when the user must specify a coordinate system, there are two methods:

  1. Easiest (and recommended) is select from the lists containing approximately 5,000 pre-defined projected and geographic coordinate systems presented in the Coordinate system dialog box. (This dialog box is available for each function in the Editor/Viewer program where a coordinate system selection may be required.) Because the lists of predefined coordinate systems are long, the dialog box contains a helpful search tool. Type in the name of a coordinate system, or just a few letters of the name, and the coordinate system is quickly found.
  2. Manually define the coordinate system using the parameter settings presented in the Coordinate System Setup dialog box (which is invoked from the Coordinate system dialog box). This might involve selecting a projection (from the list of 150+ supported projections), a datum (from the list of 900+ supported datums), distance units, Easting, Northing, etc. (Use the search tool to quickly find a projection or datum from the drop down lists.) Manual coordinate system definition is more complicated and for unusual or more advanced situations. A user typically does not need to do this.

When exporting a layer to create a new file (such as using the Editor Layer/Export function for a vector layer or File/Export to Image function for an image layer), to maximize compatibility with non-TatukGIS software products, the coordinate system information is embedded natively into the exported layer (if possible, depending on the format) and generated to external files (a PRJ file for an exported vector layer and a PRJ, World, and Tab registration file for an exported raster layer). External coordinate system files are saved to the same folder as the exported layer file and, except for the extension, have the same name as the layer file.

Notes:

  • TatukGIS coordinate system naming reflects OGC (OpenGIS) WKT definitions and EPSG codes.
  • A single open layer is regarded as a one-layer project. The software uses the coordinate system of the layer as the project (map area) coordinate system.
  • The software checks for layer coordinate system information i) embedded natively in the layer and ii) in external files (PRJ, World, TAB registration, TRN) associated to the layer. External coordinate system files are prioritized over layer embedded information and the PRJ file is prioritized over other external files.
  • The free TatukGIS Coordinate Calculator product can be a useful coordinate systems learning aid.

More about geographic coordinate systems, projections, datums, geodesy... can be found at the following resources:

Created: July 09, 2013, Modified: April 14, 2018