Scene Calibration

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The calibration of the scene coordinate system is done by means of the Coordinate System Calibration dialog in menu Tools / Coordinate System / Calibration



First the appropriate coordinate system is selected.

The next step is to choose the type of the calibration. There are two possibilities: the definition of the scene coordinate system by specifying the extents or by specifying two reference points.

Note that a mapping between two coordinate systems with parallel axes (which is the case for the internal and scene coordinate systems), which only consists of a translation and a scaling operation, is completely defined by the specification of two reference points (i.e. their coordinate values in the internal and the scene coordinate system) or by specifying the four pairs of extent values.

In order to perform a calibration by means of extents, a terrain must be loaded (only terrains define extents!). The internal extents are automatically loaded. Then the text fields under “System coordinates” must be filled with the corresponding extents in the scene coordinate system. Clicking “OK” completes the calibration.

If the calibration is specified by means of two reference points, one first has to fly to a point for which the corresponding scene coordinates are known (the camera must be placed directly above this point). Then the Coordinate System Calibration Dialog must be opened and the scene coordinate system selected. Then select “Reference Points” as calibration type and press “Get internal coord. (ref. point 1)” in order to read the internal coordinates of the first reference point. Subsequently, the corresponding scene coordinates must be entered in “System coordinates”.

Then close the dialog with the “OK” button, and fly on to the second reference point and place the camera directly above it, open the dialog again, click on “Get internal coord. (ref. point 2)” in order to read the internal coordinates of the second reference point, and set its scene coordinates, too. After clicking “OK” again, the calibration is complete.

Note that no terrain needs to be loaded when performing a calibration by means of reference points. Furthermore, for reasons of accuracy, the reference points should be as far from each other as possible.

As mentioned above, two coordinate systems can be defined in TerrainView™, the by now well known scene coordinate, and, on the other hand, the output coordinate system.

This second coordinate system can be set by means of the menu item “Tools” / “Coordinate system”. There a list of possible mappings is displayed, with the current one being marked. The mapping coordinate system only defines which coordinates are displayed in the user interface. That way, a point defined within a SwissGrid coordinate system can be displayed or changed by using e.g. SwissGrid or WGS84 coordinates.

As already mentioned, not all coordinate systems can be transformed into each other. Each geographic coordinate systems can be transformed into each other geographic system. A calibration with FlatGrid does not define a unique geographic position, so displaying it in geographic systems will not give meaningful numbers. The Internal and Normal systems are independent of the calibration and are defined only by the internal extents.

The following table lists the currently supported transformations:

Scene coordinate system


Output coordinate system

SwissGrid, WGS84, UTM

SwissGrid, WGS84, UTM, Internal, Normal

FlatGrid

FlatGrid, Internal, Normal


In case of a WGS84 output, there is a choice between two output formats, Decimal or Textual. The textual coordinates E 7° 30 30” 500, for instance, can be represented in decimal form as “7.508472” (Western longitudes and southern latitudes would have negative values).The calibration of the scene coordinate system is done by means of the Coordinate System Calibration dialog (cf. illustration above).