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How to warp or georeference a grid or image

Permanently deleted user
  • Updated

Objective:

I have an unreferenced grid/image that I need to georeference so it can be displayed on a projected map in the correct location.

Resolution:

THis is a multiple step process that includes creating a warp file and then either warping the grid or "attaching" the warp to the grid. 

Step 1: Creating the warp file:

  1. Display your image or grid to a new map - Grid and Image > Display on Map > Image (bmp, tiff, etc...).
  2. With the map selected, Coordinates menu > Georeferencing > Define a Warp.
  3. If you have known coordinates for 4 well-distributed points, use the 4-Point Quadrilateral Warp.
    If you only have a couple of points, use 2-Point or 3-Point.
  4. Select a Definition Mode > OK.

    - Interactive mode defines both old and new points directly by selecting them on the current map.
    - Semi-interactive mode lets the user select the original point from the current map, then prompts for the new position using a dialog box.
    - Manual mode uses a dialog box to prompt for both the old and new positions.

  5. Define the output coordinate projection - click Yes on the Map Projection dialog > define the projection > OK.
  6. Proceed in a clockwise or counter-clockwise fashion for the control points. This will produce a *.wrp file which is an ASCII file that can be opened in a text editor.

Step 2a: Warping a grid (*.grd) using the newly created warp  file. 

  1. Coordinates menu > Georeferencing > Warp a Grid.
  2. Select the Grid file to warp.
  3. Browse to the Warp definition file you created.
  4. Enter a name for the New warped grid file.
    To produce a new warped grid file make sure to choose the appropriate file type to save as. If you are warping a GRD, use Geosoft default *.grd. If you are warping an Image use Geosoft Color *.grd or Geotiff colour *.tif. Warping an image and not saving the resulting file as a Geosoft Color *.grd or Geotiff colour *.tif will distort the colour range of the image
  5. Once complete, display your new grid/image to a new map or to an existing projected map.

Alternatively, instead of creating a new output file, you can simply attach the warp to your image file.

Step 2b: Attaching the newly created warp to a grid:

  1. Coordinates menu > Georeferencing > Attach Warp to Grid.
  2. Browse to and select the Grid file to attach the warp to. You may have to change the Files of type to be able to select your image file.
  3. Browse to and select the Warp definition file.
  4. Click OK.
  5. Expand the Grids list in the Project explorer > right-click the file that you attached the warp to > Remove.
    This step is suggested so the image is opened in the project with the correct georeferencing information.
  6. Import the grid or image to the project from Grid and Image menu > Display.