Image 1: 3-D view of part of test area 
made with VirtuoZo's Drape function after a seamless ortho 
map and DEM was derived (Kubik, 1993). To the North-West 
some steeper hills were covered with light forest. The test area 
was covered by wide angle aerial photography at five different 
flying heights (image scales 1:1600, 1:5000, 10 000, 25 000 
and 50 000; flying heights 245m, 760m, 1520m, 3800m and 
7600m resp.). High resolution analogue photography was used, 
which can be digitised at different pixel resolution in order to 
simulate different digital camera types. Both black&white and 
colour photography was available. Ground control and a 
selected number of check points were measured by Differential 
GPS techniques. Accuracy evaluations within the tests were, 
however, usually made relative to the most accurate 
photogrammetric restitution (1:1600) in order to eliminate 
outside error sources. À joint block adjustment was performed 
in order to establish homogeneous orientation parameters for 
each photogrammetric model. The individual tests within the 
continuing project include Traditional vs.  Softcopy 
Photogrammetry, Accuracy vs. Photoscale, Accuracy vs. Scan 
Resolution, and Accuracy vs. Compression ratio (Cock, 
1995). This work was done under contract to QDPI. 
2. TRADITIONAL PHOTOGRAMMETRY VERSUS 
DIGITAL PHOTOGRAMMETRY 
These tests have been done on the largest scale (1:1600) 
photography with a flying height of 245m above the terrain, in 
order to assess the potential accuracy performance of soft copy 
photogrammetry. A traditional Digital Elevation Model (DTM) 
with regular 10 m grid was collected for one stereo model using 
our ZEISS PLANICOMP C100 Analytical Stereo Plotter. Grid 
points falling on obscured ground under trees were omitted, 
leaving over 500 points for use. No other editing apart from an 
automatic blunder elimination process within the DEM 
comparison programme was performed. The measurements 
204 
were repeated on the ZEISS C100 over the same area in order 
to assess the repeatability of measurements. A RMS value of 
0.034m (21 micron) was computed for the differences between 
the two height models. 
The film dia-positives were now scanned in a high quality 
Helava DSW 100 at a resolution of 25 micron pixel size. Using 
the same controls for absolute orientation , a 10 m DEM was 
created over the same grid of points by soft copy 
photogrammetry on our Helava DSW 750. The differences 
between the original C100 DEM and the Softcopy DEM have 
an RMS value of 0.21m. This is very large indeed, but closer 
inspection learned that a systematic bias was present of 0.18m, 
reducing the random component to 0.11m . This 18cm bias in 
height can - in our opinion - be attributed to the tufted grass and 
crop stubble which covered most of the area. The experienced 
operator pushed the floating mark into the terrain to define the 
true ground whereas the automatic correlation was done on the 
top of the tufts. This experiment taught us that it is difficult to 
make meaningful comparisons between analytical and digital 
photogrammetry as some of the basic operational assumptions 
are different and thus hard to compare. 
3. ACCURACY VERSUS PHOTO SCALE AND PIXEL 
SIZE 
For the purpose of this test the stereo image pairs were 
digitised, which cover a terrain area of 1*4 km from four 
different flying heights (1:5000 to 1:50 000). The images were 
digitised at pixel sizes of 12.5, 25, 50 and 100 micron. The 
Helava DWS 100 was used for the high resolution scans and a 
HP 3C scanner for the lower resolutions. No compression was 
applied. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996 
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