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features are digitised - in continuous or stationary mode - and then
transformed by means of DTM from the photo- to the model space, and
further to the map (or field) coordinate system.
The operations in updating correspond with those involved in data pre
editing (i.e., verifying, correcting, completing and removing) of the
original mapping. The term "updating" concerns changing the existing
data items, addition of new items, and deletion of outdated data. These
same operations are also involved in pre-editing, though updating is
based on new data sources and the techniques may differ.
Thematic mapping based on topographic or cadastral maps as geometric
datum may be regarded (from a function viewpoint) as an updating process.
The existing "datum" is supplemented with new data items. These, together
with some items extracted from the existing "datum" form a dedicated
(or thematic) data base.
Because the scope of this paper is limited, not all facets of updating
by digital techniques are dealt with. The emphasis is placed on the most
pertinent technical issues. The overall process of updating, however,
will first be outlined.
OVERALL PROCESS
General Considerations
A data base system includes formation of the original data base and its
subsequent manipulation. The DMP technique is applicable to both stages.
In new mapping, the DTM grid is supposed to cover the entire region to
be mapped, whereas in updating only local DTM data are needed, i.e., in
the zones changed.
In this paper, the term "changes" or "changed data" covers not only
changes in the existing data items, but also addition of new items, and
removal of the non-relevant data. The term "updating" applies to all
changes.
DMP for Updating
The procedure for updating should reflect the type of the existing data
base. Figure 3 shows, simplified, the alternative procedures for a
graphical and a digital data base.
Inputs
I data files I
Processes
UPDATING
BASIC DATA
FILES
GRAPHIC
UPDATING
I Updated |_
L .maps I
Outputs
digital
graphical
Fig. 3: Procedures for updating by DMP.
The "basic data files" should contain correct, complete and consistent
data - as specified for the original mapping. They form, together with
the corresponding relations (e.g., links, topological), the core of a