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Geo Referencing

Image Geo-referencing refers to placing an image in a geographical location based on coordinates that are referred to in relation to the image file. Information such as the extents in each direction and the origin of one of the corners are required so the image can be accurately displayed at its true coordinates.

ParaViewGeo offers two ways to geo-reference an image:

  1. A TIFF file where the geographical reference information is embedded
  2. A UTM based external reference file in *.tfw format


TIFF Files

The Tagged Image File Format (TIFF) can have geographic or cartographic information embedded as tags, which are used to position the image in the correct location.

When a TIFF file is loaded into ParaViewGeo, the application looks for the embedded information and places the image at those coordinates.


TFW Files

Tiff World Files (*.tfw) are files that geo-reference a *.tif file, meaning they contain the required information to accurately place the image at its true coordinates.

Geo-referencing is enabled for images using file types *.jpg, *.png, *.tif and *.tiff, and all of these formats can use the *.tfw file format to obtain the coordinate information. Although *.jpg files usually use a JPEG World File (*.jgw) for their geo-referencing information, this format is not supported in ParaViewGeo.

A *.tfw file uses the Universal Transverse Mercator (UTM) coordinate system and is written in ASCII text containing six lines of numbers.

For example, the *.tfw file for the Sudbury, Ontario10-0-0 image included in the sample data contains the following lines of information:

1.00

The X-scale, providing the distance in meters represented by each pixel; here each pixel is 1 meter

0.00

The rotation about the Y axis

0.00

The rotation about the X axis

-1.00

The Y-scale, providing the vertical distance in meters represented by each pixel, normally as a negative number because an image has its origin at the top left, whereas Northing and Easting information usually uses the bottom left corner as the origin; here each pixel is 1 meter

500193.559132

The X-reference point, indicating the horizontal coordinate (Easting) of the center of the top left pixel

5148446.69075

The Y-reference point, indicating the vertical coordinate (Northing) of the center of the top left pixel


The Geo Reference Image Reader supports coordinates in both the Northern and Southern hemispheres, and when the image file is loaded a checkbox exists to specify which hemisphere the coordinates are in.


The file names of the image file and the tiff world file must be identical for ParaViewGeo to make the connection. The Sample Data contains two such files; Sudbury, Ontario10-0-0.png and Sudbury, Ontario10-1-0.png.

When both files are loaded, the render view accurately shows their positions based on the information that was found in the *.tfw files for each image (such as the Sudbury, Ontario10-0-0 information shown in the table above).

The image shows the two Sudbury files as they appear when loaded in ParaViewGeo.



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