approach helps in reducing the search area size for
correlation, in turn reducing the overall computation
time. Interest operator selects candidate points for
matching at each pyramid of the hierarchy. There are
total three pyramids in the approach, starting from
resolution/4, resolution/2 and the full resolution
image. At each pyramid interest operator is applied on
one of the images and the approximate coordinates of
these points in the other image is obtained through a
local mapping on the previous level's conjugate
points. However system needs some seed points,
which are identified manually at the first stage (or at
the highiest level of the pyramids). The procedure
continues till the last level i.e up to the full resolution.
The number of points matched in the last level are the
final list of conjugate points for DEM generation. A
number of inbuilt checks on the reliability of the
match points are implemented.
3.5. Image Processing Functions
Apart from the simple image processing functions like
image display, roam, zoom, pixel dump, enhancement
and filtering, specific functions like (a) automatic
cartographic feature identification techniques using
pattern recognition methods (b) cartogrphic feature
dependent enhancements (c) image classification
using contexual and texture features and (d) data
merging are envisaged. In this list many are already
available, development is being carried out towards
the cartographic feature dependent enhancements.
3.6. Perspective DEM and Image Draping
For DEM editing online and for other terrain analysis,
draping of image on to the DEM is required. The tools
required here are (a) online DEM editing, (b)
perspective DEM plots (c) 2D feature coding or data
capture (d) image draping on DEM (e) image
rectification using warping methods, (f) flight
simulation/flight path generation, (g) z-tracing and (h)
image and DEM mosaicking.
3.7. Analysis Tools
In addition to the above functions, the terrain analysis
tools like (a) slope, aspect, volume and surface area
computations, (b) Line of sight computation, (c)
contouring and (d) delineation of linear features like
drainage lines from DEM etc. are also required
[ISROGIS Design Team, 1993.].
3.8. Final Map Layer Preparation and Updation
This mainly deals with creation and verification of
different map layers and interactive editing and final
compilation for printing. Different format conversions,
compilation and comparision with existing layers, line
linking and thinning are the elements required here.
483
4. SYSTEM REQUIREMENTS
The implementation of the proposed methodology
imposes four basic requirements on the system
4.1 Stereo Display
This comprises of hardware on the display monitor
and viewing glases and related software for
switching the monitor to stereo mode as a minimal
element. This facility is required at all the basic
stages of processing, viz, registration, DEM
evaluation, DEM editing, and spatial/cartographic
feature extraction. Further facilities/ functionalities
like floating cursor, z-tracing etc., for stereo
measurements have to be implemented using a
stereo display software library.
4.2 Texture Mapping
Texture mapping (TM) is the process of
projecting/visualizing a 3-dimensional phenomenonon
a 2D surface under different viewing geometry and
illumination conditions [Paul S. Heckbert, 1986.]. TM
also comprises of a hardware component and
associated software libraries. The basic concept of
DEM generation involves relating the stereo
pair/triplet to the object space (terrain). Therefore T
the implementation of any modeling algorithm
becomes very efficient, simple and elegant, when
built around the TM concept.The editing of DEM
again involves the projection on 2D display of a 3D
process. In this sense the overlay of any
topographic/cartographic theme on a stereo pair or
DEM has to be performed through TM. The updation
of any layer of map involves visual display of that
layer draped on the DEM or overlaid to be viewed in
stereo mode for interactive feature extraction, editing
and updation.
4.3 Integrated IP-GIS
The map updation involves an intermixing of image
processing and GIS functionalities as we have to
consider both the GIS map layer and the remote
sensing (RS) imagery on a common platform for the
efficient extraction of topographic features. This
leads to the requirement of a software which can
handle both vector based typical GIS operations like
proximity, union, intersection and raster based typical
IP operations like edge/line detection, and area and
size measurements, with equal ease, viz, an
integrated IP-GIS in terms of functionality.
4.4 Database Driven and OODBMS
Topomaps are moving from paper to digital form
handled by a GIS. The current and future trend is to
exploit the state-of-art in information technology and
enhance maps to provide various levels of
information at the click of a button - namely the
Multi-media extension. To handle such maps the
traditional Relational Databases have to be replaced
by Object Oriented Databases .
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
