Rigorous Sensor Modeling and Triangulation for OrbView-3 - asprs

triangulation can be performed on multiple images and sensors using tie points only in the fully weighted least
squares bundle adjustment.
Automatic Point Measurement (APM) provides a mechanism to measure tie points automatically between
overlapping imagery regardless of the image format or sensor type. APM was performed on the six input images
using a regular grid tie point pattern. The results for the tie point distribution and number are displayed in Figure 1.
Figure 1. Tie points after SOCET SET APM and MST bundle adjustment with blunder detection. The zero ray tie
points were eliminated as part of blunder detection. The maximum number of overlaps from the input imagery is
five. The three five ray points can be seen in the center of the block, which is also the location of the high resolution
orthophoto used to check the absolute accuracy of the block. The check point orthophoto footprint is shown in black.
An important element in the MST fully weighted least squares bundle adjustment is automatic blunder
detection. Enabling this feature detected and deleted 42 points from the six image block: these points are depicted in
red in Figure 1. The resultant RMS of the tie points was just under one pixel. It was determined after analysis of the
graphical display of residuals with associated imagery that the long OrbView-3 image strips were being constrained
too tightly based on the a priori accuracy estimates for the parameters. Therefore, the accuracy values for the
exterior orientation elements for the offset and linear terms in equations 3 and 4 were increased (loosened) to allow
more adjustment for these parameters. The resultant RMS for pixel space residuals decreased to 0.86 pixels.
Check points were used to determine the absolute accuracy of the six image multi-sensor triangulation. The
check points were derived from a high resolution orthomosaic that was created from digital frame images and
LIDAR courtesy of Merrick and Company. The high resolution orthomosaic has a ground sample distance of 15
centimeters. The check points were manually measured in the satellite imagery. Each check point fell within the
five-image overlap region as shown in Figure 1. Table 2 outlines the horizontal check point differences.
ASPRS 2006 Annual Conference
Reno, Nevada ♦ May 1-5, 2006
Rays Color Tie
Points
0 42
2 102
3 27
4 14
5 3