International Archives of Photogrammetry and Remote Sensing. Vol. XXXII Part 7C2, UNISPACE III, Vienna. 1999
21
I5PR5
UNISPACE III - ISPRS Workshop on
“Resource Mapping from Space”
9:00 am -12:00 pm, 22 July 1999, VIC Room B
Vienna, Austria
ISPRS
Such images may be used for the creation of planimetric image
maps at the scale of 1:10 000, but the lack of a large number of
ground control points to differentially rectify the image maps on
account of image defonnation to planimetric map accuracy 7
standards at that scale renders the expected planimetric accuracy
more to the 1:25 000 level.
Moreover, the height determination from images generally
depends on the height-base ratio of the imagery flown:
, h h
a, =± er
b c
px
with
=
h
b
c =
camera objective
or,
point error in elevation
orbital height
orbital base
principal distance (focal length) of the
"px
parallax measurement error in the order of
the point positioning error op of about 10
(im in a photographic image,
corresponding more or less to the pixel
size on the ground with the image scale
used.
Due to the very long focal length of the KVR camera of 1 m the
stereoscopic overlap conditions of that imagery will not permit
a smaller and more favorable height-base ratio than 10,
rendering the expected height accuracy of less than ± 20 m.
The present KVR 1000 high resolution images are therefore
suitable for planimetric map updates 1:10 000 or 1:25 000, but
not for digital elevation model measurements.
Cartographic satellites, which permit a better height
determination, even if they do not reach the same detectability
are the French panchromatic Spot system with 10 m pixels and
the Indian IRS-1 C system with 5.8 m pixels. Due to their
capability to incline the sensor by a mirror in cross-track
direction a favourable height-base ratio of up to 1 may be
achieved from subsequent orbits. This, however, is often a
handicap due to changing cloud cover, which severely limits
stereoscopic coverage for a time period in which the radiometry
of the ground lias not changed.
The best test result achieved thus far with Spot Pan and IRS-1C
stereo imagery are in the order of ± 5 to 10 m in elevation and ±
3 to 5 m in position, making these sensors suitable for 1:50 000
to 1:100 000 mapping in mountainous areas.
Another approach has been provided by the inflight stereo
capability 7 of the German Stereo-MOMS system. It consists of a
triple line scanner looking forward, vertically down and aft,
which has been flown for 10 days on the U.S.-German Space
Shuttle mission D2 in 1993 and which since 1996 operates on
the MIR-Space Station’s Priroda module with interruptions.
On MIR the vertical sensor yields 5 m panchromatic ground
pixels and/or 15 m multispectral ground pixels, and the fore and
aft sensors give 15 m panchromatic ground pixels. Figure 9
show's such an image over the German city of Augsburg, in
which the vertical panchromatic 5 m pixels have been fused
with the vertical multispectral 15 m pixels.
Figure 10 shows an oblique view of three processed fore, down
and aft panchromatic stereo images after the generation of a
D.E.M. and the resulting orthoimage over the area of Barcelona,
Spain.
The advantage of in-track stereo sensing is that all images to
create a DTM, orthophotos and oblique views are taken at the
same time.
The cartographic requirements for these images show, that
planimetric requirements can be met for the 1:25 000 scale, that
elevations can be determined with ± 5 to 10 pm accuracy and
that the detectability is suitable for 1:50 000 mapping.
