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9.3.2 Bundle block adjustment

While spatial resection is only applied for the determination of the six orientation parameters of one photo, bundle block adjustment allows simultaneous computation of orientation parameters and object point coordinates. A point to be computed must have been measured in at least two photos from different positions. Additional control points are necessary for positioning and strengthening the block.

At least the following input data are required:

  • Measured image coordinates of control points and tie points (new points)
  • Control points
  • Camera constant (and principal-point position)
  • Approximate values of the exterior orientation for all photos (from program RELAX).

Aerial photos as well as terrestrial photos may be used, and both may also be processed simultaneously.

For approximate values of exterior orientation, the same initial approximations must be set as for single-photo resection. The relative accuracy for neighbouring photos must be better, however, (especially for the exposure directions) as the approximate coordinates of the new points in the object space have to be calculated from the approximate photo orientations by spatial intersection. These approximations are usually computed by program RELAX and the requested precision is fulfilled. A relevant example is located in the directory \Bingo\DemoData\Simple_AT\.

For simple applications with low requirements for accuracy and for starting the first iteration of a block adjustment, the information shown above is sufficient. If high accuracy is required better approximations will be necessary in order to be close to reality. Further possibilities are:

  • To eliminate influences of systematic errors, additional parameters may be included in the adjustment. The program automatically eliminates the redundant parameters.
  • Camera constant and principal-point position can be included as observed unknowns, in order to bring about complete simultaneous calibration of the camera (the photogrammetric system), together with the additional parameters.
  • As signalised points can be measured more precisely than non-signalised points, point groups with different photo-measurement accuracies can be defined.
  • The weights of the different observation series, control points and image measurements (separated according to the aforementioned point groups) can be checked after adjustment and changed for the next adjustment (variance component estimation).
  • Different weights can be assessed for each coordinate of each control point. This procedure is recommended if, for example, the control-point coordinates have previously been determined by adjustment together with their standard deviations.