I have an unreferenced grid/image that I need to georeference so it can be displayed on a projected map in the correct location.
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:
- Display your image or grid to a new map - Grid and Image > Display on Map > Image (bmp, tiff, etc...).
- With the map selected, Coordinates menu > Georeferencing > Define a Warp.
- 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.
- 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.
- Define the output coordinate projection - click Yes on the Map Projection dialog > define the projection > OK.
- 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.
- Coordinates menu > Georeferencing > Warp a Grid.
- Select the Grid file to warp.
- Browse to the Warp definition file you created.
- 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
- 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:
- Coordinates menu > Georeferencing > Attach Warp to Grid.
- 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.
- Browse to and select the Warp definition file.
- Click OK.
- 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.
- Import the grid or image to the project from Grid and Image menu > Display.