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The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Voi. XXXVII. Part B4. Beijing 2008 
Figure 5. Diagram of task acquirement 
Secondly, it is easy for operators at the different workstations to 
cooperate during the mapping. Because tasks are created 
according to a certain bounds, a task is adjacent to eight other 
tasks. When cartographic map of a task is being interactively 
measured by an operator, the cartographic maps of other eight 
tasks will be seen in the corresponding overlapped areas by the 
operator. The work is automatically done by seamless mapping 
system. Automatic mosaic of cartographic maps is helpful for 
improving mapping efficiency. In the case of DPW, 
cartographic map mosaic is manual and cockamamie. 
Automated mosaic of cartographic maps in seamless mapping 
system is realized by the data interchange and share of 
cartographic maps belonged to different operators or 
workstations. There are two kinds of mosaic: online mosaic and 
offline mosaic. Online mosaic means that cartographic map 
mosaic is done during operators are measuring at their 
workstations. Offline mosaic means that cartographic map 
mosaic is done when some operators are not measuring at their 
workstations. Automated mosaic of cartographic maps is 
illustrated as the figure 6. 
Figure 6. Automated mosaic of cartographic maps. (A is the 
stereoscopic view in a workstation and B is the stereoscopic 
view of the same ground area in another workstation. Yellow 
contours are measured in location workstation. The blues are 
measured in another workstation) 
The two kinds of mosaic are implemented differently in 
seamless mapping system. The online mosaic is implemented 
by the peer-to-peer mode. In this mode each workstation acts as 
a servant and a client. That is, when a workstation is requested 
to provide another workstation map mosaic service, the 
workstation acts as a servant and the workstation which request 
service acts as a client. In return, when the workstation which 
request service is requested to provide map mosaic by another 
workstation, it also acts as the servant. When it is preparing to 
launch a map mosaic request, a workstation must know which 
workstations provide services and where these workstations are. 
In seamless mapping system, server which acts as a commander 
knows which workstations are working, and what tasks is being 
processed, and which tasks are the neighbours of a specified 
task, so server is acts as a location indicator. A workstation 
requests with specified task identification to server for locations 
of other related workstations before launching map mosaic. 
After it received the location information, the workstation, as a 
client, connected and communicated to other workstations to do 
map mosaic. However, not all of the workstations to be 
connected and communicated are on power or doing the 
corresponding tasks. In that case, for the workstation as a client, 
map mosaic lacks for integrity. In order to solve the problem, 
offline mosaic is implemented as a second strategy for mosaic 
in seamless mapping system. Offline mosaic is a supplement to 
online mosaic. Different from online mosaic, offline mosaic is 
implemented by the client-to-server mode. In the c/s mode, a 
mapping server as a mosaic servant and a workstation which 
launches mosaic sessions acts as a mosaic client. Because 
cartographic maps are automatically upload to mapping server 
from workstations when tasks are finished or workstation is 
going to be power off, it is convenient for a workstation to 
obtain the corresponding offline cartographic maps from the 
server. 
Automatic mosaic is very helpful for operators to collect 
cartographic map. With the help of automatic mosaic operators 
are able to collaborate on cartographic map collection. The 
collaboration improves the efficiency of cartographic map 
collection. 
Thirdly, model switch in stereoscopic measurement based on 
digital aerial photos is more convenient for operators than in the 
traditional digital photogrammetric workstation. Model switch 
is accomplished by an operator manually selecting the 
corresponding stereo pair. Model switch is a hard and 
inefficient work if there is a lot of stereo pair. The case is 
common in the photogrammetric process of digital aerial photos. 
Fortunately, the problem is solved very well in seamless 
mapping system. As described above, mapping task is 
dispensed according to extension of a sheet map, so a task 
usually contains many stereo models. These stereo models 
related to the task are found and located at the server end. For a 
workstation, it should provide an operator a way to correctly 
and seamlessly roam among these models during stereoscopic 
mapping. In order to achieve the objective, a grid based on 
object space is assigned to a task, the intervals of the grid is 
decided by taking account of information of strips in a block 
and other related block parameters. For each of cells in the grid, 
a best suitable stereo pair is located from all of related models. 
With the help of the grid and these best suitable models, model 
switch is implemented in seamless mapping system. Automatic 
model switch makes collecting cartographic map in multiple 
models be seen like as in a single large stereo model and reduce 
the unnecessary manual model switch. It improves the 
efficiency of cartographic map collection. 
Finally, raw data and intermediate data and final results are 
stored at the server end. At the client end, only intermediate 
data are obtained from the server end. It’s not serious any more 
that data on the workstation is damaged because these data are