tion can be implemented. Usually local affine transfor
mation provides satisfactory results [2] [3] [8]. Figures 3
and 4 indicate how the changes are applied to the
existing data base.
Operational characteristics
The operational characteristics concern the system as a
whole, each stage of the process, the equipment com
ponents, human factors, performance and reliability,
and the compatibility of output.
The overall system properties concern issues such as
versatility and flexibility of the DMP system; modular
set-up; phased, parallel and decentralised operation; ba
lanced work load and time-lineness of data flows; and
compatibility of components and of data. Most of these
properties are interdependent and are strongly influen
ced by the system design.
The main phases of the process, i.e., the preparation,
mensuration, transformations, and plotting, are serial
and can be time-delayed. Moreover, the operations are
modular in each phase. Hence, optimisation of each
phase contributes to the optimisation of the overall
process.
From a human engineering point of view, it is advan
tageous that in each phase the specific skills can be em
ployed. The most delicate phases are preparation, men
suration, and pre-editing the changed data. These ope
rations should be thorough and time-efficient.
The equipment architecture may be composed of the
existing components [61, though a simple dedicated
instrument for measurements, permitting stereoscopic
observation is preferable. The xy-digitising from a single
photograph should be combined with the x-parallax
measurement/digitising. Moreover, a simple plotting
device should be attached to procedure a check plot in
real-time. Such a device is not needed if a graphic
display terminal for interactive operation is connected.
The accuracy, time-efficiency and reliability depend pri
marily on the precision of the measuring equipment and
on the skill and care of the personnel involved. Thorough
preparation is essential. Potential sources of errors and
failures are the identification of control and tie points,
especially on generalised maps, and separate measure
ments of the differential heights and the planimetrie
locations. In the latter case, mistakes in indexing or in
the sequence of measurement are likely to occur [8].
Errors in DTM and in differential heights cause radial dis
placements which may be significant, especially near the
photo-edges, when terrain surface is rough [2] [3].
The updated information should be compatible with the
existing graphical and the anticipated digital data base
system(s). Compatibility concerns the data structures,
formats and codes, and the (added) relational data, i.e.,
to provide flexibility in manipulating and representing the
basic data.
Conclusion
The recent achievements in the field of data base tech
nology give reason to reconsider the existing techniques
for updating maps. An up-to-date approach should serve
two purposes, i.e., to update the existing map series and
to contribute to a gradual transition from graphical to
digital data bases. By accumulating the changes, adding
new data items and relations and converting the existing
ones into a digital format, a digital data base can be
gradually built-up.
It seems rational to anticipate that there will be an in
creasing transition from the original mapping to updating
NGT GEODESIA 82
the existing data bases. The traditional economic and
performance considerations about the alternatives of
„updating" orre-mapping" are no longer applicable to
digital data bases. Correct „old" data should be preser
ved and supplemented by the „changed" and „added"
new data, even if more than 50% of the total information
has changed. Re-mapping is justified, however, if a
higher accuracy is required.
The operations typical for updating by DMP are involved
in the preparation, mensuration, and the geometric
transformations. The properties of DMP in updating are
listed below, separated according to technical and
management views.
The technical properties are:
Control points and local DTM data can be extracted
from existing topographic maps. Aerial triangulation
and full DTM coverage are therefore not required;
Operations can be restricted to local zones of
changes (except change identification and external
orientation);
The transformation and correction algorithms are ex
changeable, which provides versatility and flexibility;
The DMP output is suitable for updating graphical
and digital data bases;
The DMP software can be made compatible with
other existing data base software systems;
The height of any point can be determined as a by
product.
Some properties important for work management in
clude:
The process is phased and thus operations can be
parallel and decentralised;
Existing equipment can be used;
Each operation employs specific skills;
The control data, inclusive DTM, need not be avail
able in the phases preceding the transformation
stages.
DMP is less feasible when the required accuracy is very
high and/or when the terrain relief has changed. From
this list of properties, however, it follows that DMP is a
potential alternative to updating by means of ortho-
photographs. It represents a supplementary photogram-
metric technique to stereomapping, it meets the require
ments of an up-to-date base system, and it may contri
bute to gradual transition from graphical to digital data
bases.
A cknowledgement
The author wishes to express appreciation and thanks to
Dipl.-lng. K. Tempfli for his critical comments.
References
1. Allam, M. M. A review of data acquisition systems present
and future and their effect on cartographic information
systems. ISP Congress, Commission IV, Hamburg, 1980.
2. Beotra, L. M. Topographic map revision by digital mono-
plotting. Enschede, ITC, M.Sc. thesis, 1981.
3. BeseniCar, J. Digital restitution from single photographs for
cadastral purposes. Enschede, ITC, M.Sc. thesis, 1976.
4. Case, J. B. Automation in photogrammetry. ISP Congress,
Commission II, Hamburg, 1980.
5. Kölbl, O., Pradervand, J. C. Interactive digital stereoplotting for
the renovation of cadastral survey. ISP Congress, Commission
IV, Hamburg, 1980.
6. MakaroviC, B. Digital mono plotters. ITC-Journal, Enschede,
1973-4.
7. Masry, S. E., McLaren, R. Digital techniques for map revision
and detecting errors in digitised data. University of New
Brunswick, Department of Surveying Engineering, Technical
report no. 40, Fredericton, 1977.
8. Radwan, M. M., MakaroviC, B. Digital mono plotting system
improvements and tests. ITC-Journal, 1980-3, Enschede.
299
