Introduction
Today many mapping institutions all over the world are
increasingly confronted with the problem of updating
existing maps. Updating should reflect the dynamics in
geo-information. Thus it is useful to reassess the existing
concepts, methods and techniques for updating in the
light of the present and anticipated future environment,
and to promote further development of the updating
techniques.
The objective of this paper is to outline a photogram-
metric digital approach for updating existing graphical
and/or digital data bases. Attention is focussed on digi
tal mono-plotting (DMP) technique [4] [6]*), especially
on change identification and extraction, mensuration
and the subsequent geometric transformations.
Updating of maps has been regarded as an autonomous
process, and the techniques have been predominantly
graphical and analogue. At present, a transition is taking
place from analogue to digital techniques and thus from
graphical to digital data bases. The techniques and
equipment can be differentiated as indicated in figure 1
MONO
DIGITAL
STEREO
ANALOGUE
Fig. 1. Photogrammetric techniques and equipment for updating.
The subject of this paper is digital mono techniques,
which can, however, be further classified as shown in
figure 2.
DMP permits conversion of line (and point) data, col
lected from a single photograph, to the orthogonal (or
another) projection. The planimetrie features are digi
tised 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) co
ordinate system.
The operations in updating correspond with those in
volved 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items, addition of new items, and deletion of outdated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 also 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
problems. The overall process of updating, however, will
first be outlined.
Overall process
General considerations
A data base system embraces the formation of the origi
nal data base and its subsequent manipulation. Updating
is an integral part of 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. Nevertheless, most of the
operations are identical or very similar in both stages.
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 alter
native procedures for a graphical and a digital data base.
Inputs
I Existing I
basic files
Existing maps j
New images
DMP
I Changed
I data files I
I New basic"!
I data filesj
J-New graphic!
Updated
UPDATING
BASIC DATA
FILES
I Updated
maps
graphical
J~New graphic!
I data files I
digital
Outputs
De nummers 1 t.m. 8 verwijzen naar „References" aan het eind
van dit artikel.
Fig. 3. Procedures for updating by DMP.
The „basic data files" should contain correct, complete
and consistant data as specified for the original
mapping. They form, together with the corresponding
relations (e.g., links, topological), the core of a digital
data base. A „graphic data file" (or „plot file") contains
only selected data items, provided with symbols, text
and drafting instructions. Moreover, the features can
also be generalised [1] [2],
As a byproduct of the „graphical" variant of updating,
the intermediate digital products i.e., the changed data
files, may be collected with the aim of gradually forming
a digital data base, while the graphical one remains pre
served. An outline of the procedure for the transition to
a digital data base, however, is beyond the scope of this
paper.
Overall process definition
The overall process of updating is carried out in several
sequential stages (fig. 4). The initial stages, such as
reconnaissance, planning and air mission, are not con
sidered here because they are not specific for DMP. This
also applies to cartographic reproduction.
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295
ORTHOPROJECTION
(using DTM)
RECTIFICATION
I (flat terrain)
1 Photographic
data
Line data
Fig. 2. Digital mono techniques.
