The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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Camera 
RC 30 
DMC 
DMC 
Year of flight 
2004 
2006 
2007 
Flying altitude (m) 
4700 
4500 
2000 
Focal length [mm] 
153 
120 
120 
GSD [cm] 
45 
45 
20 
Number of fotos 
136 
326 
234 
Number of flight lines 
7 
8 
10 
End lap / side lap |%] 
60/25 
60/25 
60/25 
Table 4: Block configurations 
For the three blocks 3 DEMs were created with Match-T V5.0 
setting the grid width approximately to the recommended value 
of 30 pixels; i.e. 15m for 45cm GSD and 7.5m for 20cm GSD. 
Low smoothing was chosen allowing the modeled surface to be 
close to the correlated point cloud. During the evaluation phase 
Match-T DSM V5.1 was released, which allows to further 
decrease grid width towards values of 10 pixels and below. 
With that version additional DEMs were created with a grid 
width of 10m and 5m for 45cm GSD and also 5m and 2m for 
20cm GSD. For the comparison only “good” points were used, 
which were not classified by Match-T to have low redundancy 
or bad accuracy. 
LIDAR data served as an independent reference, collected in 
January 2007 with an OPTECH ALTM 3025 system from 
2 250m flying altitude. Parallel flight lines were flown with 
20% side lap and a mean point density of 0.33 points/m 2 in the 
non-overlapping areas. After ground classification this data is 
converted into a regular DTM with 2m grid width. Its accuracy 
is in the dm-level. 
Test area was a 7.6km x 5.4km wide region close to the city of 
Tarragona in Spain (see Figure 2). It includes a 0.8km 2 sized 
test-site in a flat area (TSflat), which contains neither 
buildings nor higher vegetation and a 2.8km 2 sized test-site in 
the city of Tarragona (TSurban). 
Figure 2: Test area (7.6 x 5.4 km 2 ) with the two test-sites 
TS flat (upper left) and TS urban (lower right) 
The grid points of the different versions were compared to the 
LIDAR data. The results are graphically represented in Figure 3. 
DEMs in different configuration were created for the entire test 
site (Match-T V5.0 only) and for the test sites TS flat and 
TS urban. The descriptors in Figure 3 indicate whether a digital 
(DMC) or an analog camera (RC30) was used, followed by the 
GSD in cm and the grid width deduced from that flight data. 
An appendix “_v51” is added if Match-T DSM V5.1 was used; 
e.g. “ana45_10m_v51” represents the results of a 10m spaced 
DEM obtained with Match-T DSM V5.1 from RC30 images 
having a ground pixel size of 45cm. 
The DEM calculated for the entire test site as well as for 
TS flat are compared to the regular spaced 2m DTM LIDAR 
data, representing the ground surface without vegetation and 
buildings. The DEM calculated for TS urban is compared to 
the unclassified LIDAR point cloud representing also 
vegetation and buildings. The results for the three different test 
sites represent three different levels of accuracy. The 
represented standard deviations a are the results after filtering 
out all differences exceeding 3a. In case of test site TS flat 
1-2%, in the other cases an average of 15% of the differences 
was filtered out. 
The most accurate results are obtained for test site TS flat, 
where the DEM points are compared to the LIDAR DTM on a 
bare ground surface. In this flat area the DEM interpolation 
error is small and the comparison is more exact and reliable. 
Digital and analog images of 45cm ground pixel size result in 
more or less the same accuracy (1/2 ground pixel) with slight 
advantages for the DMC results. The digital images of 20cm 
GSD result in 8 to 9 cm accuracy reaching the accuracy level of 
the LIDAR data. The variation of the grid width has no 
significant impact on the results. 
In test site TS urban the DEM grid points are compared to the 
unclassified LIDAR points. Especially in urban areas the 
differences are much bigger, since the DEM grid points can not 
represent the height discontinuities at the edges of buildings or 
other man made objects. Figure 4 shows a profile of the 
unclassified LIDAR points (white) and DEM grid points at lm 
spacing derived from DMC images of 20cm GSD (red). The 
example shows, that some details resolved by LIDAR are not 
resolved by Match-T. For the 45cm pixels the accuracies 
obtained with analogue images are slightly better. The 10m and 
5m spaced DEM, however, show big gaps where most of the 
points were classified to have low redundancy or bad accuracy. 
With DMC images a 10m and 5m spaced DEM from 45cm 
GSD could be derived without problems.