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Georeference Application Layer

Use this dialog to georeference a standard application layer or a raster application layer directly in the drawing.

Where can I find the dialog?

Right-click in the vertical list field and select Tools - Georeference application layer...

Using the Dialog

Click the minimum required points or more in the local application layer, and then the corresponding points in the map (terrain model area).

Depending on the selected transformation type, the program calculates the parameters for the transformation. You can perform the transformation on the local application layer with the Transform button.

Transformation Types

Helmert transformation (2D) is defined by four parameters and is a widely used transformation method. The method takes into account that the systems do not have coincident origins, that the coordinate axes are not parallel, and that the systems do not have the same scale. With a Helmert transformation, the shape of objects does not change.

Helmert transformation (3D) is a mathematical method for transforming coordinates from one three-dimensional reference system to another. This method, also called seven-parameter transformation, is used when working with 3D data.

Affine transformation additionally takes into account different scales in the x and y directions. The method can, for example, be used for data that has been scanned from paper maps that have changed shape.

You can also generate a report with the result from the calculation.

Procedure

  1. Select the application layer to be georeferenced and choose the function from the tools menu.
  2. Select transformation type.
  3. The program suggests the minimum required points. Change this if necessary.
  4. Press Point and register points in the local application layer.
  5. Zoom to the map and register the corresponding points in the map.
  6. Press Transform to perform the function.

Example of georeferencing application layer with three reference points

Georeferencing with World File versus Image Warping

Georeferencing with a world file links a raster to a coordinate system without changing the pixel geometry, while image warping involves geometric deformation of the image through resampling.

  • World file - Tells where the image is
  • Image warping - Changes the image itself

Georeferencing with World File

What it is:

Linking an image to a real coordinate system (e.g., UTM, WGS84).

How:

A world file (.tfw, .jgw, etc.) stores a simple, global transformation:

  • Scaling (pixel size)
  • Rotation
  • Translation (placement in the map)

Important:

  • The pixel image itself is not changed
  • Only the coordinate interpretation is changed

Mathematically:

An affine transformation (linear).

Image Warping

What it is:

Physically deforming the image by moving pixels.

How:

  • Linear or non-linear transformations
  • Often uses control points
  • Requires interpolation

Important:

  • Pixel values are changed and resampled
  • The image gets a new shape