Georeferencing an image by coordinates

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Balazs Hober
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Georeferencing an image by coordinates

Postby Balazs Hober » Wed Jan 21, 2009 1:45 pm

This instruction set applies to DigiTerra Explorer 5 desktop version (it works on the mobile version also, but it will be more comfortable on the desktop version) and should help you to georeference/assign a coordinate system to a scanned airphoto or an uncorrected satellite image. Georeferencing is the process of assigning coordinates to control points on the image of known locations that can also be easily distinguished on a paper map or other referenced data layer.

Please, follow the next steps:
1. Tap the New Map button on the toolbar and set the map type (projected, geographic) and the coordinate precision of the map layers and the projection.
2. Tap the Layers button on the Pan frame or on the toolbar and tap the Add Layer(s) button on the Layers window (or use it directly from the toolbar).
Image Image Image
3. Tap the raster file you would like to add and press the Open button. You don't need to rescale the image to fit it within the window, Fit to Display is an automatically process to uncorrected raster images.
4. Zoom in to the approximate area that is covered by the image to which these layers will be added. This does not have to be exact as it is done just to provide you with an easier workspace. Tap the Raster orientation button on the toolbar and place three control points (P1, P2, P3) onto the map. This will place a cross mark on that location.

Note: it is a good idea to zoom in on your image when adding control points for better accuracy.

Image Image
5. Right click on the placed point on the image and enter Easting and Northing coordinates. Press OK. Repeat this step with each control point (P1, P2, P3).
6. When you are satisfied with the georeferencing process, you have two options for saving the parameters of the georeferencing:
- as a WORLD file: Open the Layers panel, press the Source button and press Save World file button.
- save the parameters into an .EXP project file. Select Save Map icon from toolbar.
Downloadable sample project
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