JUNE 2000www.geoinformatics.comJUNE 2000
In parallel with this develop-
ment, a highly competitive
market place has been created
in which the prices of DPWs
have dropped quite significant-
ly. In turn, this has allowed a
far greater number of users to
adopt the technology. The long
predicted supplanting of ana-
lytical plotters (APs) by DPWs
has at last taken place, at
least in terms of sales of new
systems. However large num-
bers of these older instruments
remain in production in map-
ping agencies and companies
and a limited number of new-
build APs are still being sold.
Furthermore there are still a
significant number of sales of
analogue-to-analytical conver-
sions (by Qasco. Adam
Technology, LH Systems, etc.)
and of PC-based upgrades to
existing APs (by DAT/EM, ABC
Software Developers, etc.). The
starting point or base line for
this review of recent develop-
ments in the digital pho-
togrammetric field will be the
three papers produced by the
authors (Walker & Petrie, 1996
and Petrie, 1997a and b) at the
time of the last Congress held
in Vienna. The present article
aims to review the develop-
ments and trends that have
taken place since then and
thus prepare participants for
what they can expect to
encounter in this area at the
Amsterdam Congress. However
the specialist field of close-
range, non-topographic pho-
togrammetry will not be cov-
ered in this review.
High-Precision Film Scanners
At the top end in terms of per-
formance, sophistication and
price (>$120,000), the two
major suppliers - Z/I Imaging
and LH Systems - have contin-
ued to develop and add refine-
ments to their existing
SCAI/PhotoScan TD and DSW
models respectively. Using
these highly sophisticated sys-
tems, there is now a greater
acceptance of scanning nega-
tive roll films on the part of
users. Partly this comes from
the elimination of the need to
make diapositives prior to
scanning. However it is also
the result of the developments
in dodging and colour balanc-
ing software that have taken
place over the last two or
three years. Both of these
high-end systems require pow-
erful high-performance Unix
(SGI or Sun) or Windows NT
workstations to drive them.
Examples are the ScanServer
from Z/I Imaging with dual
Pentium III processors and a
built-in RAID disk array and the
new DSW500 from LH Systems
with a similar specification. The
DSW500 allows pixel sizes
down to 4mm, which is attrac-
tive to the intelligence commu-
nity. In 1997, ISM purchased
the rights to the OrthoVision
950 scanner from its former
constructor, XL Vision, re-
named it XL 10 and dropped
its own DiSC device. The XL10
scanner also offers automatic
roll film transport, but occupies
a somewhat lower price range
at around $95,000. The Vexcel
Imaging VX4000 scanner also
occupies an intermediate posi-
tion in terms of sophistication
and cost (circa $85,000) and
continues to be unique in
terms of its ability to handle
large-format (23 x 46cm) aerial
photography used primarily for
military mapping purposes. At
a much lower cost (circa
$55,000) is the simpler Wehrli
RasterMaster which has recent-
ly introduced a revised and
improved RM-2/NT model.
However this still does not
possess a roll-film capability.
The GeoSystems Delta-Scan
from the Ukraine (cost $35,000
in 1996) was shown at the last
Congress in Vienna. It also
accepts quite large films such
as the Russian 30 x 30cm for-
mat. A new model with colour
capability, a roll film unit and a
smaller pixel size than before
is promised for the Amsterdam
Congress.
An interesting newcomer to the
film scanner field is Vexcel
Imaging Austria. This company
has introduced its UltraScan
5000 scanner which is manu-
factured on its behalf by Wild-
Austria. This will be shown at
the forthcoming ISPRS
Congress. The device has a
photogrammetric specification
in terms of its measuring accu-
racy, geometric resolution and
radiometric performance speci-
fications. There is also an
optional roll film capability
available. However it is also
aimed at the much larger
graphics arts and printing/pub-
lishing industries and at foren-
sic applications and the medi-
cal imaging market in order to
achieve volume sales and be
available at a lower cost
($40,000). Thus the develop-
ment of the UltraScan 5000
has been carried out in cooper-
ation with a Danish company,
Purup Eskofot, that is active
within the graphics arts field
and with a Swedish company,
Cox Analytical Systems, in the
forensic field. Their particular
versions of the scanner tech-
nology are called EskoScan
and Maxcan respectively.
Lower Precision Scanners
It must be said that quite a
number of commercial mapping
companies have also adopted
the still lower cost (<$25,000)
scanners that are in
widespread use in the graphics
arts and desktop publishing
(DTP) worlds. Usually these
devices are designed to accom-
modate A3-sized originals,
including hard copy prints as
well as transparencies. In gen-
eral, they have a much lower
geometric accuracy than the
purpose-built photogrammetric
film scanners. Thus they tend
to be used with larger pixel
sizes and on less demanding
applications than the specialist
devices. Furthermore they lack
the motorised roll film drives
and sophisticated software that
are necessary if negative roll
films are to be scanned and
digitized. While the Agfa
Horizon and Sharp JX-610 are
examples that have been used
previously, newer models that
have come into use recently
are the Circon, Linoscan and
Nexscan flatbed scanners (all
with an A3 format) from
Heidelberg CPS - which has
taken over the Linotype-Hell
organisation. Other similar
devices include the Mirage II
flatbed scanner from the
Taiwanese company, UMAX
Technologies, and the new
Agfa T5000 scanner.
Interestingly a special kit,
called ScanCorrect, comprising
a precise grid plate and accom-
panying software - including
automated measurement of the
positions of the crosses con-
tained in the scanned image of
the grid - is on offer from the
Russian Racurs company. This
is designed specifically to carry
out the geometric calibration
of DTP scanners with a view to
their use in digital photogram-
metric applications. A similar
kit has also been available
from the Canadian DVP compa-
ny for some time and another,
called MasterScan, is being
introduced by the Siscam com-
pany from Italy. It will be inter-
esting to see whether tests of
these new lower cost scanners
are reported at the Amsterdam
Congress and, if so, what
results are obtained in terms
of their geometric accuracy and
resolution on the one hand
and their radiometric perfor-
mance on the other. Previous
tests of the older devices gave
rather poor results.
DPW Hardware
With regard to the computer
hardware and operating sys-
tems being used in DPWs, a
major change since the last
Congress is that the combina-
tion of a Sun or SGI graphics
workstation and the Unix OS
has steadily lost ground. Now
virtually every supplier of
DPWs offers systems that uti-
lize Pentium-based PCs with
current processor speeds up to
733MHz running under
Windows 95 or NT. Indeed
many suppliers only offer their
DPWs on the PC platform. For
power applications on both
scanners and DPWs, use is
made of PCs equipped with
dual processors and threaded
code by LH Systems and Z/I
Imaging. Furthermore, many
users have turned to using
locally built PCs as the basis of
their DPWs rather than use the
Dell, Compaq, Gateway and
other branded machines which
are more expensive, but do
offer world wide support.
Memory is also much less
expensive than before and
many DPWs are now equipped
with 0.5 to 1 GB of RAM, which
can be employed very usefully
in many of the DPW's internal
operations. As many readers
will realize from using their
own home computers, a 15 to
20 GB hard disk is now quite
commonly found on those PCs
used as the basis for a DPW.
But the problems of storing,
archiving and managing large
volumes of image data are
now looming ever larger as
more photos are scanned and
more DPWs are installed. The
storage and management of
tens or hundreds of terabytes
of image data are now being
considered instead of the hun-
dreds of gigabytes that were
being handled before.
As solutions to these problems,
on the one hand, the issue of
data compression has risen to
the fore with the wavelet-based
rivals, MrSID and ECW, joining
the fray alongside the longer
established JPEG method. On
the other hand, many mapping
agencies and companies have
been forced into buying RAID
drives or jukeboxes of high
density cartridge tape drives for
the storage of the huge vol-
umes of image data that are
now being handled. Needless
to say, in this context, network-
ing has also become more
important with the widespread
adoption of Fast Ethernet oper-
ating at 100 Mbits/sec. instead
of the older 10-BaseT Ethernet
standard. Another previously
important matter - the wide
choice of stereo-viewing sys-
tems - has mostly been settled
into a straight choice between
the two methods - the "active"
StereoGraphics CrystalEyes or
"passive" NuVision systems -
based on the use of alternating
screen images. Interestingly
both suppliers now offer both
possibilities! Finally, most of
the DPW system suppliers
appear to have settled for the
use of a 3D mouse or a tracker
ball with a Z thumb-wheel for
manual control and measure-
ment functions. Though some
users still use the standard
mouse and keyboard which, in
the opinion of the authors, is
far from optimal for the pur-
pose.
Digital Photogrammetric Syste ms Approach Maturity
A Global Survey of System Suppliers
After the first commercially marketed digital photogrammetric workstation (DPW), the Kern
DSP1, was introduced at the 16th ISPRS Congress held in 1988 in Kyoto, there followed a rapid
development of the technology, including high-precision film scanners as well as DPWs. This
was evidenced by the large number of these systems that were introduced and demonstrated at
the next two ISPRS Congresses held in Washington (in 1992) and Vienna (in 1996). Now, twelve
years after that first introduction and approaching the 19th Congress to be held in Amsterdam
in July, the technology is much more mature. Thus real innovations are fewer and, in general,
there is now a concentration by the system suppliers on making numerous small but useful
additions and refinements to existing systems. The emphasis with these improvements is to
make the systems faster, more capable and more user-friendly than their predecessors.
By Professor Gordon Petrie and Dr. Stewart Walker
The Z/I Imaging PhotoScan TD flatbed scanner showing the automatic roll-film unit
for use with negative films. The scanner is controlled by a powerful Intergraph TDZ
2000 workstation running Z/I Imaging's AutoScan software. (Courtesy Z/I Imaging)
The new UltraScan 5000 high-precision
scanner from Vexcel Imaging Austria
with the optional roll-film adapter in
place to handle uncut rolls of negative
film. (Courtesy Vexcel Imaging
Austria)
A highly competitive
market place has been
created in which the
prices of DPWs have
dropped quite
significantly.
Now virtually every
supplier of DPWs offers
systems that utilize
Pentium-based PCs with
current processor speeds
up to 733MHz running
under Windows 95 or NT.

JUNE 2000www.geoinformatics.com
DPWs from the Major Vendors
or Groups
1. Again, if one starts with the
the two market leaders - Z/I
Imaging and LH Systems - the
current situation is rather dif-
ferent in each case. In the case
of the two partners in Z/I
Imaging - Intergraph and Zeiss
- the former had already
adopted the PC/NT platform as
the standard for its
ImageStation Z series of DPWs,
whereas the latter had
remained faithful to SGI graph-
ics workstations for its PHODIS
DPW. Obviously a decision will
now have to be made by the
new Z/I Imaging company as to
whether to continue both of
these separate product lines
or, as many observers expect,
to standardize on the
ImageStation DPW. In conjunc-
tion with this decision will be
another closely associated one
as to whether to continue to
utilize the substantial number
of the add-on packages or
modules that are sourced from
outside the Z/I Imaging combi-
nation. These include MATCH-
AT (for automated aerial trian-
gulation); MATCH-T (for
automated DEM generation);
PATB/PATM-GPS (for block
adjustment) and SCOP (for
DTM operations), all of which
come from Inpho, and the
SPOT software from the Trifid
Corporation, which has now
been taken over by ORBIMAGE.
Besides which, Intergraph had
already taken on Atlantis
Scientific's EarthView radar
processing packages and it
now appears that these will
continue to be offered under
the Z/I Imaging banner. The
ImageStation Z series contin-
ues to be developed with ever
more powerful Pentium proces-
sors (including twin and quad
processors), while the SSK kit
is available to convert a stan-
dard PC into a DPW at a lower
cost.
2. Similarly the LH Systems
SOCET SET software suite is
continuing to be developed
with the incorporation of an
ever widening set of sensor
models - for aerial frame and
panoramic cameras; for
Landsat, SPOT, IRS-1C/D and
JERS-1 OPS space scanner
imagery; for RADARSAT, ERS
and JERS-1 SAR imagery; and,
of course, for its own new air-
borne digital sensor (pushb-
room scanner). Besides those
modules such as HATS - now
renamed APM (Automatic Point
Measurement) - that form part
of the SOCET SET suite, refine-
ments have been made both
to the ORIMA product for trian-
gulation and to the PRO600
module for feature extraction
within the MicroStation
GeoGraphics environment. Both
of these products have been
available for some time on the
company's APs: now they are
available for use with the DPW.
Recently LH Systems has also
developed a lower-cost, entry-
level DPW product called DP
Digital Plotter. This comprises a
minimum set of SOCET SET
and PRO600 modules together
with a stereo-viewing capability
to carry out routine feature col-
lection. The overall SOCET SET
suite is still being developed in
parallel for both the Intel/PC/NT
and the Unix platforms, since
several large U.S. government
mapping agencies are continu-
ing to opt for the latter.
Besides LH Systems, SOCET
SET is also being offered sepa-
rately by one of its parents,
BAE SYSTEMS (the successor
to GDE Systems and Marconi
Integrated Systems) to military
and defence users. In addition,
a sub-set of SOCET SET forms
the basis of the OrthoEngine
AE package which is sold by
PCI Geomatics into the remote
sensing/GIS market. PCI sup-
plements this with its own
OrthoEngine SE package which
handles a wide range of space
imagery.
3. Autometric is another fairly
large supplier of full-function
DPWs in the shape of its
SoftPlotter suite. This is sup-
plemented by its stand-alone
OrthoKork package, which is
one of many orthophoto pack-
ages that are on the market.
Till now, SoftPlotter has only
been offered on Unix-based
Sun and SGI graphics worksta-
tions, while OrthoKork is only
available on PCs. However the
Autometric Web site now men-
tions SoftPlotterNT, so one
may expect a new Windows-
based product to emerge soon.
ERDAS continues to offer the
OrthoMAX module which is
based on Autometric's software
and carries out aerial triangula-
tion, automatic DEM extraction
and orthorectification within
the ERDAS IMAGINE environ-
ment on Unix-based machines.
However the ERDAS company
has also decided to produce
its own digital photogrammet-
ric products for PC platforms
running Windows 95, 98 and
NT. This will comprise three
main elements - (i) aerial trian-
gulation and orthorectification
(called OrthoBASE); (ii) feature
extraction from stereo-models
(Stereo Analyst); and (iii) auto-
mated DEM extraction from
both aerial photos and space
imagery. The first of these
modules, OrthoBASE, was
released at the 1999 ASPRS
Convention, while the second,
Stereo Analyst, was introduced
at the ASPRS Annual
Convention held in Washington
in May. The European launch is
scheduled to take place at the
ISPRS Congress in Amsterdam
in July. Besides the version
contained within the IMAGINE
environment, Stereo Analyst
will also be available both as a
stand-alone package and inte-
grated into the ArcView GIS
environment for the purpose of
stereo-viewing and stereo-plot-
ting with 3D Shape files. Once
all the ERDAS modules have
been completed, the company
could well become an impor-
tant player in the DPW market
place - as it is already in the
remote sensing field.
DPWs from Smaller North
American Vendors
Under this heading, one may
consider the PC-based DPWs
from ISM, DVP, R-WEL, KLT,
DAT/EM and Amsatek, all of
which originate from North
America. In general, one can
say most of them concentrate
on the data acquisition of 3D
data using manual stereo-plot-
ting techniques for map pro-
duction and GIS applications.
Some also offer a separate
package for orthophoto pro-
duction, while one or two offer
the capability of mapping from
SPOT stereo-pairs.
(a) ISM from Canada is a
strong player in certain mar-
kets, especially Canada and
Spain. Besides its main DPW,
the DiAP-NT, ISM is also offer-
ing its simpler, lower-cost DiAP
Viewer product which is
designed specifically to carry
out feature extraction employ-
ing stereo-viewing, -mensura-
tion and -superimposition tech-
niques. This is done using
An LH Systems DPW with twin screens running the SOCET SET software under
Windows NT on a Dell PC. The operator is utilizing a 3D hand controller to control
the position of the measuring mark and is viewing the stereo-model in 3D with the
new lower-cost CrystalEyes wired spectacles from StereoGraphics. (Courtesy LH
Systems)
(a) The on-screen user interface of the
Measurement Tool of the new ERDAS
Stereo Analyst product. This features
re-sizable windows showing the
images at different scales.
(b) A visualization of the 3D data
acquired by Stereo Analyst for part of
the Los Angeles urban area. (Courtesy
ERDAS)

JUNE 2000www.geoinformatics.com
pre-oriented stereo-model files
established by aerial triangula-
tion or used previously for
photogrammetric mapping. A
further recent development has
been to introduce an Automatic
Image Mensuration (AIM) mod-
ule for the point transfer and
measurement of control and tie
points using image matching
techniques. This is carried out
in association with the Aerial
Triangulation Manager (ATM)
which has a full interface with
the Inpho PATB-GPS block
adjustment package. Like most
vendors, ISM also offers a
stand-alone orthophoto pro-
duction capability in the form
of its SysImage package
together with the well known
TIN/CIP terrain modelling pack-
age. Given that ISM also has
the XL-10 high-precision scan-
ner on its product list, the
company now offers the most
complete range of digital pho-
togrammetric products outside
the two market leaders.
(b) Another Canadian company,
DVP Geomatic Systems, is also
quite strong in certain coun-
tries, e.g. in Greece, Turkey,
Belarus and Mexico, as well as
in North America. The company
offers quite a wide range of
digital photogrammetric prod-
ucts, including modules for
orthophoto generation and
monoplotting, besides its cur-
rent model of DPW - called the
DV400P. Like ISM, it also offers
a simplified 3D digitizing sta-
tion using pre-oriented stereo-
models. This associated with
an interesting and innovative
new product called the Active
Virtual Stereo Index that was
introduced at the GIS 2000
Conference held recently in
Toronto. This creates an index
of these pre-oriented stereo-
models and displays them in a
window on the monitor screen.
Thereafter the user can mark
the desired area within this
window and the relevant
stereo-model will be displayed
within another window on the
screen. Thus the user can
move freely within the seam-
less mosaic of stereo-models
while still maintaining stereo-
viewing of the terrain.
Furthermore, rather unusually
for this class of DPW, the com-
pany also offers its DVP-SPOT
module which allows 3D data
collection from stereo-pairs of
SPOT digital images. This
development has resulted from
a collaboration with the
Canada Centre of Remote
Sensing (CCRS).
(c) Turning next to considering
the smaller American compa-
nies, R-WEL, which, like DVP,
was an early university-derived
entrant into the digital pho-
togrammetric field, continues
to offer its DMS package main-
ly for feature extraction and
map revision purposes.
However, unusually for this
group of vendors, it also offers
automated DEM generation
and orthophoto production,
both from stereo-pairs of aerial
photos and SPOT space
images.
(d) KLT Associates is very well
known in the photogrammetric
world for its Atlas digital data
collection software used with
analogue stereo-plotters and
DPWs from Europe
At the Kyoto ISPRS Congress in
1988, the main photogrammet-
ric system suppliers from
Western Europe - Wild, Kern,
Zeiss, Matra, Galileo-Siscam,
OMI, etc. - with their analytical
plotters completely dominated
the market. No one then could
have predicted or envisaged
the dramatic changes that
have taken place since, which
have resulted in the system
supply side largely moving
elsewhere, especially to North
America. Small numbers of APs
are still being made in the for-
mer Wild, Zeiss and Galileo
factories, re-branded under the
LH Systems (SD2000/3000), Z/I
Imaging (Planicomp P3/33)
and Siscam (Stereobit and
Stereocart) labels respectively.
Furthermore the dominant aeri-
al cameras are still being man-
ufactured in the first two of
these factories. But in the
DPW field, the situation has
completely changed.
(a) The major European player
is now the German company
Inpho with its MATCH (-AT, -T
and -I), PAT (-B and -M), SCOP
and SKIP products. While it
does sell these packages
directly, quite a number of its
sales are made through system
suppliers such as Z/I Imaging
and DAT/EM that have adopted
some or all of these packages
as add-on modules to their
DPWs. On its part, Inpho has
made no effort till now to
enter the field of feature
extraction and orthophoto gen-
eration, though obviously it
has the capability to do so.
However Inpho has concluded
an agreement recently with the
Stellacore Corporation to devel-
op, distribute and support its
well known OrthoVista
orthophoto mosaicing package,
that had been marketed previ-
ously by Zeiss.
(b) As noted above, the Zeiss
PHODIS DPW faces an uncer-
tain future under the new Z/I
Imaging grouping. Which
means that, if this disappears,
then only Siscam of the tradi-
tional European AP suppliers
will remain in the DPW field. At
the 1996 Vienna Congress, the
Siscam company showed its
Stereodigit (a very basic DPW
equipped with twin small
screens) and Microdigit (a bat-
tery powered version with tiny
LCD screens). Both of these
DPWs were based on PCs. In
the interim, both of these
This example of the ISM DiAP-NT is
equipped with handwheels, a footdisk
and foot pedals for precision stereo-
plotting. The infra-red emitter for syn-
chronisation of the "active" wireless
stereo-viewing glasses with the alter-
nating screen images is located on top
of the display monitor. (Courtesy ISM
Europe)
The DAT/EM Summit PC which allows
feature extraction and map compila-
tion to be carried out in AutoCAD or
MicroStation using StereoGraphics
CrystalEyes "active" stereo-viewing sys-
tem. (Courtesy DAT/EM)
The user interface of the new DVP
Stereo Index product introduced at the
recent GIS 2000 Conference held in
Toronto. The right-hand window of the
monitor screen shows the index or
overview of all the stereo-models in the
area of interest. The left- hand window
shows the selected stereo-model at an
enlarged scale. This can be viewed
either using cheap, simple anaglyphic
(red/blue) spectacles or a more sophisti-
cated and more expensive viewing sys-
tem such as that from StereoGraphics
using its CrystalEyes alternating shut-
ter spectacles. (Courtesy DVP
Geomatics).
APs. It also offers digital pho-
togrammetric products in the
shape of its Atlas/DSP digital
stereo-plotter (DPW) for feature
extraction and 3D digital data
collection and its Atlas/Ortho
and Atlas/TIN products.
(e) DAT/EM's Summit PC, first
announced in 1997, took some
time before it appeared in a
fully operational form last
year. This late arrival has
meant that, as yet, it only has
a small share of the DPW mar-
ket. However the company has
been very active in upgrading
Intergraph APs through its
IMA-to-DMA conversion kits
and in the supply of its well
known DWG/CAPTURE and
DGN/CAPTURE data collection
software for analogue and
analytical stereo-plotters. The
Summit PC also places an
emphasis on feature extraction
using DAT/EM's own CAPTURE-
NT software operating directly
within AutoCAD or
MicroStation. Like Z/I Imaging,
DAT/EM also offers the
MATCH-AT, MATCH-T and PATB-
GPS products from Inpho as
add-on packages to the
Summit PC.
(f) Amsatek has been active in
the GIS field for some time -
its current products in this field
include the AMSA98/NT digital
mapping system; the AMSA-RIS
(Relational Information
System); and the Connex-A/I
software for the bi-directional
conversion of data between
the AutoCAD and MicroStation
CAD packages. To complement
these, it also offers the AMSA-
DC (Digital Compiler) for fea-
ture extraction from stereo-
pairs and the AMSA-Digital
Orthophoto module for
orthophoto generation using
DEMs derived from other
sources.

JUNE 2000www.geoinformatics.com
appear to have been dropped.
Now, for the Amsterdam
Congress, Siscam will show its
much improved and more
capable DPW, called
Stereometric, together with
modules for orthophoto gener-
ation (Orthomap), automatic
DEM generation (A.D.A.), pro-
cessing of DEMs (DEM
Manager) and block adjustment
(B.A.T.).
(c) Finally, a small Finnish soft-
ware company, ESPA Systems
Ltd., has entered the market
with its Espa Kernel, Espa
Block, Espa Ortho and Espa
City products. These are sched-
uled to be demonstrated in the
Technical Exhibition at the
Amsterdam Congress.
DPWs from the Former Soviet
Union
Gradually quite a number of
digital photogrammetric prod-
ucts from the former Soviet
Union countries have become
known and have entered the
market.
(a) At the 1996 ISPRS Congress
held in Vienna, a Ukrainian
company, GeoSystems, made
an impact showing quite a
comprehensive range of prod-
ucts, including its
Stereoanagraph AP as well as
its Delta-Scan photogrammetric
scanner, mentioned above, and
its Delta-Station DPW. All of
these products utilize the
PC/Windows platform. These
products continue to be
offered, finding their principal
market in the former Eastern
Bloc countries, but with sales
too in Western Europe, Asia
and Africa. Further develop-
ments of all of these
GeoSystems products are
promised for the Amsterdam
Congress.
(b) Another PC-based system,
the Siberian Digital
Stereoplotter (SDS), that had
been developed at the Siberian
State Academy of Geodesy in
Novosibirsk, was also shown
and demonstrated at Vienna,
but little has been heard of it
since.
(c) However a stronger and
more robust development has
been the recent introduction of
a more comprehensive range of
digital photogrammetric prod-
ucts from the Racurs company
based in Moscow. This includes
the PHOTOMOD DPW with
modules for automated aerial
triangulation (AT) and automat-
ic DEM generation (DTM),
besides feature extraction from
stereo-models. So far, it has
made its main impact on map-
ping agencies in the former
Eastern Bloc, but it has now
appointed agents in Western
Europe, the Middle East and
East Asia and has already
delivered DPWs to Syria and
Saudi Arabia.
DPWs with a Chinese
Connection
(a) The most prominent player
in this group is Supresoft with
its VirtuoZo DPW which runs
on both the Unix and Windows
NT platforms, producing DEMs
and orthoimages as primary
output. Stereo-measurement
and 3D data collection may
also be carried out using
VirtuoZo. Extension modules
provide automatic tie point
generation and an interface to
a PATB module provided by
Inpho. The company had its
roots in developments that
took place at the Wuhan
Technical University of
Surveying & Mapping in China.
Its DPW was then given a
Western interface with the aid
of an Australian company
based in Brisbane. Since then,
it has acquired a world-wide
distribution network and now
has a significant presence in
the DPW market place.
(b) Another much more recent
entrant is the Desktop Digital
Photogrammetric System
(DDPS) which has been
launched by another Australian
company, 3D Mapper, based in
Perth in Western Australia.
From its literature, the product
again appears to have a strong
Chinese connection, in that
DDPS has also been developed
by graduates from Wuhan. The
principal components of DDPS
are StereoMaker (which carries
out the orientation of stereo-
models), StereoMapper (for 3D
vector mapping) and
OrthoMaker (for orthophoto
generation). Once again, this
has been developed solely for
PCs running Windows 95, 98
or NT.
Remote Sensing System
Suppliers
It is interesting also to assess
the position of the remote
sensing system suppliers with
regard to the digital pho-
togrammetric field. As dis-
cussed above, ERDAS is now
making a determined and seri-
ous effort in this particular
area with the introduction of
its OrthoBASE and Stereo
Analyst products. PCI has also
had some success with its
OrthoEngine packages. But, in
general, the other mainstream
suppliers of remote sensing
image processing packages -
e.g. Earth Resource Mapping
(with ER Mapper), MicroImages
(with TNTmips), Research
Systems (with ENVI), etc. -
have all been content to limit
themselves to orthophoto gen-
eration, mosaicing and visual-
ization capabilities. However
Sensor Systems with its
RemoteView product running
under the Unix OS does offer
stereo-viewing and measure-
ment using the rational polyno-
mial coefficient (RPC)
approach. This utilizes a non-
rigorous image geometry
model that has come into
widespread use within the U.S.
intelligence and military com-
A VirtuoZo DPW with twin screens -
the one used for stereo-viewing and
measurement; the other used for the
display of the plotted features, system
information, menus, etc. (b) A layered
colour perspective representation of the
area of the Columbia Glacier in Alaska
constructed from a DEM generated by
a VirtuoZo DPW. (Courtesy SDS)
munities. On the basis of this
model, the image supplier
computes the RPC data for
each image and distributes this
data to the user along with the
actual image. This has a partic-
ular application when the user
has no information about the
geometry of the camera or
imaging sensor, in which case,
it is not possible to employ a
rigorous geometric model. This
possibility is also offered by LH
Systems and PCI. But in gener-
al, one can say that most of
the remote sensing system
suppliers do not offer rigorous
geometric modelling, triangula-
tion and highly functional fea-
ture collection from stereo-
models. However these
companies do offer a much
more extensive range of data
input and output formats;
image processing algorithms;
analysis and classification
tools; and image/map fusion
capabilities than the pho-
togrammetric vendors. Finally
one must note that, besides
the many different orthophoto
engines offered by the pho-
togrammetric and remote sens-
ing system suppliers, a number
of independent vendors, e.g.
the Vexcel Corporation with its
OrthoGIS, also offer packages
that will generate orthophotos
from single images, given the
availability of DEM and orienta-
tion data from another source.
Conclusion
In our review of DPWs for the
1996 Congress (Walker & Petrie
1996), we wrote then that,
when we (or our successors)
make our report to the ISPRS
2000 Congress, it will be a
success story centered on
reductions in the cost of map-
ping. This prediction has
turned out to be not too far
wide of the mark. Users now
have a large range of film
scanners and DPWs with a rich
variety of solutions, capabili-
ties and price levels from
which they can make their
choice.
Professor G. Petrie, Department of
Geography & Topographic Science,
University of Glasgow, Glasgow, G12
8QQ, Scotland, U.K. Internet:
http://www.geog.gla.ac.uk/~gpetrie, e-
mail: g.petrie@geog.gla.ac.uk
Dr. A. S. Walker, LH Systems LLC,
10965 Via Frontera, San Diego,
California, 92127-1703, U.S.A. Internet:
http://www.lh-systems.com,
e-mail: walker@lh-systems.com s
Users now have a large
range of film scanners
and DPWs with a rich
variety of solutions,
capabilities and price
levels from which they
can make their choice.