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Image Geo-referencing

In this tutorial we will look at how images can be geo-referenced within ParaViewGeo, specifically with the use of Tiff World (*.tfw) files. The alternate is to use *.tiff or *.tif files that have embedded tags containing the required information.
  • Locate and open the Sample Data folder.
    • Note that there are two sets of files for Sudbury, including a *.png and a *.tfw file.
    • ParaViewGeo supports geo-referencing for four image file types: *.png, *.jpg, *.tif and *.tiff.
    • If any of these image files have a *.tfw file in the same folder that has the identical name, the coordinates referenced in the *.tfw file are used to accurately place the image.

  • Open the Sudbury, Ontario10-0-0.tfw file using a text editing program such as notepad.
    • Note that the file contains six lines of text and uses the UTM (Universal Transverse Mercator) coordinate system.
      • Line 1 is the X-scale, identifying the distance in meters represented by each pixel.
      • Line 2 is the rotation about the Y axis.
      • Line 3 is the rotation about the X axis.
      • Line 4 is the Y-scale, identifying the vertical distance in meters represented by each pixel, usually as a negative number because image files have their origin at the top left corner, whereas Northing and Easting information usually uses the bottom left corner as the origin.
      • Line 5 is the X-reference point that identifies the horizontal coordinate (Easting) of the center of the top left pixel.
      • Line 6 is the Y-reference point that identifies the vertical coordinate (Northing) of the center of the top left pixel.
  • Using ParaViewGeo, load the Sudbury, Ontario10-0-0.png file.
    • ParaViewGeo's Geo Reference Image Reader supports UTM coordinates in both the Northern and Southern hemisphere, and will automatically search for the *.tfw file when one of the four image file types is loaded.
    • The Object Inspector contains a Northern Hemisphere checkbox to identify which hemisphere the coordinates belong to (the default is to identify coordinates as belonging to the Northern hemisphere).
    • Since Sudbury is in the northern hemisphere, we can simply press Apply.
    • An image of part of the Sudbury area showing the northern edge of Georgian Bay appears in the render view.
  • Now also load the Sudbury, Ontario10-1-0.png file.
    • Again we can simply press Apply since the northern hemisphere is already selected.
    • A new image is added to the render view, clearly showing Lake Wanapitei, and it aligns perfectly with the first image to show the whole Sudbury basin.

  • If we had a *.tiff or *.tif file with the coordinates embedded as tags, we could simply load that file into ParaViewGeo without requiring any additional files. The image is positioned at the coordinates specified in the embedded tags.

We have now looked at how image files can be loaded into ParaViewGeo so that they are placed at their true coordinates by referencing geographical information in an associated *.tfw file.

Click on the Disconnect icon and choose Discard to clear the pipeline.

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