The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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3.2 DLG 
DLG is a very important product of digital photogrammetric 
systems and it is extensively used by geospatial-related fields. 
DLG is a pivot in the project of Surveying and Mapping West 
Regions of China. 
SPOT-5 HRS imagery is mainly used for mapping topographic 
maps by manual stereoscopic measurements. Because the 
ground resolutions in two directions of images are different, the 
SPOT-5 HRS images should be performed geometric 
transformations such as zooming and rotating. A scene of 
SPOT-5 HRS stereo pair covers a 120km*600km area in the 
ground. Topographic mapping from SPOT-5 HRS stereo pairs 
challenges the current workflow of the traditional digital 
photogrammetry, so a new mapping workflow is proposed for 
mapping topographic map from high resolution satellite 
imagery. 
In practical production, a new mapping system for high- 
resolution satellite images called Seamless Mapping System 
(SLM) developed by Supresoft Inc. is applied. The mapping 
system is built on a high-speed network and with the distributed 
processing capability and with the help of the system, 
collaboration of mapping among different operators is 
supported. In the mapping system, Mapping from SPOT-5 HRS 
stereo pairs are firstly divided into a certain of sub-tasks 
according to task planning strategies. The usual strategy, as 
illustrated in figure 5, is to divide the mapping into a lot of 
standard map sheets according to these map sheets’ ground 
bounds. 
Figure 5. Map sheet dividing strategy in Seamless Mapping 
System. . 
Once mapping tasks are created at a server end and dispensed 
by administrators to operators for manually stereoscopic 
measurements, operators are able to access the related images 
and orientation data at their workstations. It is not necessary for 
operators to obtain all SPOT-5 HRS images instead of partial 
data of HRS images related to a map sheet. By the dividing 
strategy, mapping of a SPOT-5 HRS stereo pair is able to 
collaborate by many operators and more efficiently processed. 
Figure 5. Combination of HRG and HRS images for 
stereoscopic measurements of DLG 
Contours are main features of a topographic map. The workload 
of measurement of contours from stereo pair has about 80% of 
the whole works of mapping a topological map. The efficiency 
of producing topographic map depends on the efficiency of 
measuring contours. The most inefficient approach of 
measuring contour is surveyed manually. An alternative 
efficient approach is that contours are interpolated from 
DEMs/DSMs which are automatic extracted from HRS and 
HRG stereo pairs. By using the Multi-photo Geometrically 
Constrained Matching technique, DEM or DSM can be 
automatically extracted from SPOT-5 HRS and HRG imagery. 
Then contours are interpolated automatic from DEM, the 
workload of topographic map is consumedly reduced. 
The figure 6 shows there DLGs of different geomorphic type 
collected from SPOT-5 HRS images and HRG images in the 
west regions of China. 
In order to solve the occlusions of objects on the HRS stereo 
images as shown in the figure 5, a HRG image and two HRS 
images are combined to form three stereo pairs for manual 
stereoscopic measurements.