distribution of tie points between the SPOT images and 
the aerial photography. 
2. METHOD 
2.1 Data 
The project was located in northern Alabama in an area 
with flat to hilly terrain. The block of aerial photography 
was centered over Priceville, Alabama. The imagery used 
in the project included a stereo pair of SPOT Level 1A 
panchromatic images acquired on two successive dates, 
28 Janurary and 29 Janurary 1988. Both images were 
acquired with the HRV 1 sensor with look angles of Left 
13.4 degrees and Right 19.9 degrees, respectively. The 
aerial photographs consisted of a block of 27 1:24,000 
scale frame photographs arranged in 4 east/west flight 
lines. These were acquired using a Wild RC-10 camera 
on 28 February 1991. The diapositives were scanned on a 
PS1 scanner at a resolution of 22.5 microns, and were 
stored in a JPEG compressed dat format. Flight lines 10, 
9, and 8 entirely overlapped the SPOT stereo model, while 
flight line 7 only partially overlapped the SPOT images. 
The ground control was collected from two different 
sources. For the standard aerial triangulation ground 
control was established through a differential GPS survey 
using one roving receiver. In this survey the ground 
control points were set up at prominant photo-identifiable 
locations. The control was referenced to the State Plane 
1983, Alabama West Zone coordinate system. For the 
triangulation, the standard deviation of this control was 
set at 0.25 feet. The ground control used in the multi- 
sensor triangulation was collected from 1:24,000 scale 
United States Geological Survey (USGS) 7.5 minute 
topographic maps. To collect this control, the map sheets 
were registered into a design file using an affine 
transformation of the neat line corners. The registration 
was accomplished with less than 0.3% RMS error. The 
ground control points were located at the center line of 
road intersections, and were digitized to a precision of 1 
centimeter in the design file. The points were then 
transformed into latitude/longitude coordinates referenced 
to the World geodetic System 1984. Elevations for the 
control points were interpolated from the maps’ contours. 
Standard deviations for the X,Y,Z coordinates of the 
control were set at 10 meters. | 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B3. Vienna 1996 
   
2.2 Data Analysis 
Several runs of the multi-sensor triangulation were made 
to test the effect of different configurations of ground 
control and tie points on the accuracy of the solution. The 
bundle adjustment used was the Trifid Multi-Sensor 
Triangulation for SPOT and aerial photography. 
The first run used 11 ground control points distributed 
throughout the SPOT model. None of the control was 
measured on the aerial photographs. Tie points between 
the SPOT images were collected at an interval of 
approximately every 1000 pixels, and both SPOT images 
were tied to each aerial photograph in the block with 
between 12 - 16 tie points per photograph. Diagnostic 
points were also collected. The second run used the same 
configuration as the first run, but was limited to only 5 
ground control points. The control was distributed with 
one point at each corner of the SPOT stereo model, and 
one point in the center of the model. The third run 
changed the configuration by limiting the tie points 
between the SPOT images and aerial photographs to just 
the corners of the block. The fourth run changed the 
configuration by limiting the tie points between the SPOT 
images and the aerial photographs to just the upper left 
corner of the block. In the final run, the same 
configuration as the first run was used, but this time only 
included a single SPOT image in the simultaneous 
adjustment. 
Two conventional aerial triangulations were run. Their 
results were used as baselines to which the multi-sensor 
triangulation results were compared. The first 
triangulation used 16 GPS derived control points, while 
the second used 19 control points collected from the 
USGS quadrangles which covered the project area. In 
both triangulations, 6 - 8 pass points were collected per 
model, along with 4 - 6 tie points per strip. 
2.3 Data Collection 
The multi-sensor project setup was accomplished using 
Intergraph’s ImageStation Photogrammetric Manager 
(ISPM) software. The setup involved weighting the - 
sensor parameters, extracting initial estimates for the 
SPOT ephemeris from the SPOT leader files, organizing 
the images into their proper orbital configurations, setting 
the convergence criteria for the adjustment, and setting 
the object grid parameters. 
Point mensuration was accomplished using Intergraph's 
ImageStation Digital Mensuration (ISDM) software. The 
same Interior Orientation (IO) parameters were used in 
each run of the multi-sensor triangulation. The IO 
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