e Orthophotos can be generated in monochrome or in
colour. The DEM can either be a previously digitised
DEM or it can be generated patch by patch during
orthophoto generation using image correlation techniques.
e The image correlation routines utilise monochrome
images for higher resolution.
System configuration in production
In a production environment it is recommended to do the
orthophoto sheet editing, preparation and printing on a separate
computer. A network is the most suitable method to transfer
the data from the PC running the orthophoto generation on the
PROMAP system to the editing workstation.
Data acqusition workstatíon 1
— workstation
| P Plotter/Printer
a
rn
A :
Editing and printing
1
PR
bj
PROMAP System
Data acqusitíon workstation &
toptionall
quee mmm mmn
: a H Network Server
t... Ebeee
PROMAP System
Fig3 Production system configuration
Orthophoto Operation
The ADAM PROMAP Orthophoto Generation functions allow
an operator who is accustomed to analytical stereoplotter
operation to create an orthophoto covering the model loaded in
the PROMAP in a simple user-friendly manner.
It can operate in either of two modes.
e Using a pre-existing DEM. In this mode, a DEM from
any source must be imported for use. It can be digitised
using ADAM cartographic software or imported from some
totally external source. In this mode, the system can
generate an orthophoto covering an entire photograph if
required.
e Simultaneously with automatic DEM generation. In this
mode, the DEM for each patch is generated and then the
Orthophoto segment for the patch is generated immediately
after. In effect, an orthophoto can be generated even when
you have no DEM for the model.
Orthophoto mosaicking and printing
Orthophotos generated from the ADAM PROMAP can be
exported into GIS systems or other image management
software. They can also be printed directly to any Windows
supported raster plotter.
Orthophotos are generated one model or photograph at a time.
Users can export these orthophoto sections for processing by
another package or can use the simple mosaic options provided
and join them into completed map sheets. Simple grid and
feature overlay functions are also provided.
Automatic DEM generation
The Automatic DEM works on one patch at the time. With the
current hardware configuration the patches generated by the
frame-grabber are 720x540 pixels. Control points or any
available height information of sufficient accuracy is used for
initial approximations of ground levels. Depending on the
terrain, image pyramids up to 3 levels are generated. Least
squares image matching techniques are utilised to determine
conjugate points.
The operator can check the correlated points on the PC monitor
viewing the stereo model with a basic 3D display.
The precision of the correlated points are expected to be better
than 0.5 pixel.
The correlated ground points are placed on a regular grid based
on one diapositive. As an additional feature, ground points can
also be correlated on a regular ground mesh.
Performance testing
At the time of writing this paper, it is anticipated that a DEM
of a model consisting of 60,000 points and a colour orthophoto
will be generated in under 1 hour. Extensive tests are planned
to evaluate the performance of the system.
DEM grid size on plate Imm 0.5mm
Number of DEM points 20200 80799
Number of patches 297 297
DEM generation time 9 min 27 min
Orthophoto generation 52 min 52 min
Table 2 Predicted timings and sizes for orthophoto production
(estimated from prototype at time of writing)
(Those interested in final test results should contact ADAM
Technology directly.)
Product release
The ADAM PROMAP Orthophoto Generator will be unveiled
at ISPRS in Vienna, July 1996. Beta testing will begin after
ISPRS. ADAM PROMAP Automatic DEM is expected to be in
Alpha testing soon after ISPRS.
Conclusion
The ADAM PROMAP Automatic DEM and Orthophoto
options will offer a very cost efficient solution to the problem
of producing digital orthophotos.
The ADAM PROMAP can still be used as a conventional
analytical stereoplotter, however, the advanced automatic
features offer great productivity increases.
There are a number of further options that could be developed
for the system in the future. For example, automatic interiors,
automatic relative exteriors, high resolution scanning, feature
digitising assistance functions are among the options that have
been identified for the future. Once the basic hardware is
installed, these options will only require a software upgrade.
758
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
