Bundle Block Adjustment

The Bundle Block Adjustment menu functions shows the following submenu:

There are two adjustments possible.

During the adjustment procedure, corrections are calculated for projection centres, orientation parameters, and object points.
The new improved coordinates for the object points and the projection centers, and the new orientation values are immediately effective in the Strabo Project.

• Soft Bundle Block Adjustment: this version also calculated corrections for the coordinates of GCP's.
  (GCP = Ground Control Point.)

• Hard Bundle Block Adjustment: this version calculates no corrections for the GCP's.

The calculation of the bundle block adjustment can take some time.
One phase in the adjustment is the inversion of a very big matrix, especially the first times with rough values this inversion can take much time.
The adjustment minimizes the corrections on the observations.
If these corrections are to big after finishing the adjustment, use the next menu function to inspect these bad tiepoint measurements.

The residues for the object points with big corrections can also be consulted by selecting 'Goto Bad Object Point…' function in the adjustments menu.
A list of all the tiepoints with high residue values is given.
This function can only be used immediately after the execution of the bundle block adjustment.
Because residues are not saved in a project file, you cannot inspect 'bad' objectpoints and their respective tiepoint measurements after opening an existing project.

After calculation of the adjustment it is possible to view the bad points using the next dialog:

Pressing the 'Show' button you can show the bad tiepoints, correct them, and redo the adjustment until there are no bad points anymore.

The results of the adjustments can be saved by selecting the 'Save listings' option.
Several files containing results and statistics of the adjustment are then created.

This 'Save Listings' function creates the following files:

• '{projectname} AllResultsWithResidues.txt': this text file lists the calculated terrain coordinates of the projection centers, the orientation parameters, the object point terrain coordinates and the GCP's with each their respective MSQE values and the standard deviation.
  In case of hard positioning no MSQE values for the GCP's exist, the mentioned MSQE's are in that case replaced by the residues calculated by resection.
• '{projectname} EO.txt': this text file lists the terrain coordinates of the projection centers and the flight orientations.
• '{projectname} ObservationsWithResidues.txt': this text file lists the coordinates of each tiepoint with their residue expressed in the camera coordinate system.
  Tiepoints with high residue values are indicated with an arrow at the end of the record.
  The indication occurs when the w-value is greater the 'wtestlimit1' (see values in Strabo.ini).
  These points are selectable through the 'Goto Bad Object Point...' dialog and are ready for manual inspection and correction right after the adjustment calculation.
  At the end of the listing it is mentioned how many percent of the points has a w-value smaller than 'wtestlimit1' and how many percent of the points have a w-value smaller than 'wtestlimit2'.
• '{projectname} RemainingParallax.txt': this text file lists the object points with the degree of parallax remaining in respective object point.
• '{projectname} Statistics.txt': this text file lists the main statistic results of the bundle block adjustment, i.e. type of adjustment, number of control points, photos, object points, image point measurements and observations, the degree of freedom, the a-priory standard deviation for the observations and control points the number of iterations, the sigma Naught and the result of the F-test.
• '{projectname} TiePoints.txt': this text indicates how many times each image point has been measured and in which photographs.

w-value: the w-value is the ratio between the residual of the observation and the standard deviation on the observation.
Sigma Naught: mean square error of the observation resulting from the adjustment of the observations.
F-test: the ratio of Sigma Naught and the a priori standard deviation on the observation. This value is a value on which you can decide to accept the adjustment results or not.

1. If F-test is to big (a lot greater than 1), you can find the bad points in the file 'projectname ObservationsWithResidues.txt'. They are indicated with an arrow at the end of the bad point's line. These points have a big w-value in the last two columns. The w-value is the ratio between the residual of the observation and the standard deviation on the observation.
   • In case of bad points, the (x,y) residue value is in fact the vector from the image point to the adjusted position of it's corresponding object point. The adjusted location is in fact the image point coordinate plus the residue vector for not rotated images. For rotated images you must subtract the residue vector from the image point location to get the adjusted location.

• During the adjustment, several actions can be taken like:
  • GCP points can be updated or added,
  • New tiepoints can be measured.
    After each adjustment the user can immediately measure new tiepoints: new approximations have to calculated in that case.
• The results of the adjustment are always immediately effective in the project.
  This means that after an adustement you can start:
  1. Viewing Stereo models.
  2. Using the Softcopy tool for data collection.
  3. Measuring DEM points using the DEM Viewer.
  4. Start a orthorectification process.