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Georeference Image File

Use this dialog to georeference an image file for use in a BGR application layer.

Where do I find the dialog?

Select the BGR application layer in the vertical list, right-click, and choose Properties..., then Georef...

Using the dialog

The image file can be a map background with hand-drawn information, a scanned drawing with a map grid, a drone image, or similar, which you want to display together with your project data.

Before you can georeference an image, you must prepare two application layers: one with image coordinates and one with map coordinates.

You need three or more points in the application layers. The same value for S_OBJID indicates that the point represents the same location in both the map and the image.

Clicking the Test Calculation button calculates the affine transformation parameters. If you have more than three points, the standard deviation for a coordinate value is also calculated.

Using Test Calculation button

Image coordinates must be digitized in the image, while the corresponding map coordinates can be entered manually, imported as measured points, or digitized in the base map.

You can do the entire job in the same drawing, but it may be practical to have two drawings: one with image coordinates and one with map coordinates.

This way, you can arrange the drawings side by side and avoid a lot of zooming from the image at 0,0 to map objects far away.

Side-by-side drawings

The actual georeferencing of the image is performed with Calculate georeferenced image. A new image is then created. For TIFF files, the georeference information will be written to the file, but you can also generate a world file in the same folder as the BGR application layer. The default file name is the same as the original image with the postfix _GEOREF. This can be changed if needed.

Suggested workflow

Preparation

  1. Create a drawing, for example, "Georef map coordinates" (you can also use an existing drawing), with the template Georeferering.aly.
  2. Create a BGR application layer, for example, "BGR - image nn".
  3. Create a GMI application layer, for example, "Map coordinates - image nn".
  4. Depending on the task, create three or more points in the GMI application layer using one of the following methods:
  5. Import the measured points
  6. Enter the map coordinates for the points manually, for example, based on the coordinate grid in the image file
  7. Add an FKB application layer and digitize the points
  8. Create a drawing, for example, "Georef image coordinates", with the template Georeferering.aly.
  9. Create a BGR application layer, for example, "BGR Image coordinates - image nn", and add the image to be georeferenced.
  10. Create a GMI application layer, for example, "Image coordinates - image nn".
  11. Arrange the windows vertically.
  12. Digitize three or more image points with the same S_OBJID as the map coordinates.

Georeferencing

  1. Activate the drawing "Georef map coordinates".
  2. Create a BGR application layer, for example, "Georeferenced image(s)".
  3. Select Georef...
  4. Select the image to be georeferenced and the application layers with image and map coordinates (note that both drawings must be open for all application layers to appear in the list).
  5. Click Test Calculation and check the report.
  6. Click Calculate georeferenced image when the test calculation is accepted.
  7. Click Yes to add the georeferenced image to the BGR application layer.