Working with Tie Points

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Working with Tie Points

Working with Tie Points

Tie points play a key role in TerraPhoto data processing workflows. Tie points provide a method for solving camera parameters and improving the positional accuracy of images. They are used for camera calibration at the beginning of the processing workflow and later, for internal and external positional improvements of the actual project data. See Chapters Camera Calibration and Improving Image Positioning for detailed information.

Tie points are differentiated into different types. They can occur as point or line features but, for reasons of simplicity, the term ‘tie points’ is used for both in this documentation if no separation is necessary.

The software handles and uses tie points differently for airborne and mobile ground-based missions. For airborne missions, the tie point mode is only available if a ground model is loaded in TerraPhoto. For mobile missions, a ground model is not required for working with tie points. However, there are a few tie point types which are only available for airborne or mobile missions. Finally, there are differences in the aims for which tie points are collected.

Airborne missions:

Collect a small number of tie points for all cameras of a mission and distributed over the whole project area for adjusting misalignment angles in the camera calibration file.

Collect more tie points until as many images as possible are well-defined by tie points. Improve the misalignment angles, principle point coordinates, and lens distortion parameters iteratively while working with tie points.

Collect a big number of tie points for images in order to adjust the positioning for each image individually.

Mobile missions:

Collect a small number of tie points for all cameras of a mission and distributed over the whole project area for adjusting misalignment angles in the camera calibration file.

Collect tie lines of type Straight line for solving the lens distortion values in the camera calibration file.

Collect tie points of types Known depth and/or Depth at regular distances in order to derive fluctuating corrections of the trajectory drift in TerraMatch.

 

TerraPhoto Lite does not have any of the tie point tools.