A and of DEM
tem (scanner as
>uId be made by
>lution DEM.
3,1 village near
-cause a recent
iuse it is quite
area: they are
rences from top
nts range from
km.
ing the hill side
lined downhill;
:e a main front
arge blocks are
’ a pattern of
several areas,
active. The hills
shes and trees,
it, resulting in a
ige but (though
the quarry, in
'7, consists of a
9 ^ 52) at the
ampilation of a
stained in the
; flown around
rom the banks,
dfy the exact
>f the project is
the same area,
ie span and to
a topographic
id in order to
I generation by
Three aspects
?ht and camera
les along and
versus terrain
,t height means
areas prone to
A longer focal
and also help
r perspective
ant, this would
worsening the
•s, compare to
s adopted in
undermine the
as only for the
ised on this
il lenght have
ling flight.
:ct in advance,
and terrain
>EM generated
digitized with a DWS 100 scanner of the IRIS lab at
JRC Ispra at a resolution of 12.5 urn (about 7 cm on
the ground). Thought one of the goal of the
investigation was to find out the best resolution value
to be adopted, no test have been performed at the
original resolution: the amount of data (more than 300
MB per Image) proved too hard to handle, so images
have been resampled to 25 pm. Further test will be
executed by using a DTP scanner to check dependency
on scanner performance.
3. TEST ON DEM GENERATION
Two digital photogrammetric systems have been used
in the test: a high end system (hereafter called system
A) and a low cost one (system B). An area of about
320000 square meters has been selected for the test.
5' to provide more than 80000 points on a PII 350
machine.
Fig. 2 - Aerial view of the Botticino quarry
which encloses most of the quarry and an area mostly
covered by trees and bushes (see Fig. 2). After
performing a semi-automatic image orientation
(automatic relative orientation with operator-assisted
check for possible mismatches) System A was set on
DEM generation with adaptive strategy: this means the
system is capable of adjusting the matching parameters
to the terrain and texture characteristics.
Points were determined on a mesh 2 m wide, without
supplying any a priori information on the terrain in the
form of breakline location and so on. It took less than
5045700. OC-C-i.
i ì H
5045600.00-
5045500.00-
5045400.00-^
5045300.00—^.
The values have been compared to the interpolated
reference data, resulting in a 2m RMS of the
discrepancies, with about 50% of the values in the
range (-0.5: 0.5m) m and a bias of about 0.7 m.
Figure 3 shows a plot of the DEM errors larger than 1
RMS (10% of the data) with the DEM contour lines in
the background. As it could be foreseen, the largest
errors occur on terrain breaklines.
5045200.00-^ cy
5045100.00- .
5045000.004
5044000.004
5044600.00-
5044700.00
1602300.00
1602500.00
1602700.00 1602900.00 1603100.00 1603300.0-
-1-CX3 is> -2.00
-2,00 to 2.00
2.00 » 30.7«
Fie. 3 - DEM error plot for system A (2 m grid)
