International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004
2.2 Reference Data Sets:
2.2.1 DEM Data Sets of Montmirail: The term digital
elevation model or DEM is frequently used to refer to any
digital representation of topographic surface.
Projection Information:
Geodetic system: NTF (Nouvelle Triangulation de la France)
Ellipsoid Clarke 1880 IGN
Prime meridian Paris
Projection Lambert II
Altimetric system IGN 1969
2.2.1.1 Laser DEM of Montmirail: Laser DEM is the digital
elevation model derived from LIDAR datasets. Actually the
DEM produced from Lidar datasets gives us digital surface
model, which is a combination of digital terrain model and man-
made objects/ vegetation cover (or canopy).
Description of DEM is as given below:
Format: BIL+HDR
No. of Rows & Columns = 3418 & 2034
Pixel Size =5m
Accuracy = | m rms
MAPUNITS: METERS
ULXMAP: 809452.50 m
‘
ULYMAP: 1919252.50 m
2.2.1.2 BDTOPO DEM of Montmirail: There is very less
information about BDTOPO DEM present in the Word file sent
with HRS evaluation datasets. It has been assumed that
topographic maps are the basic input for the topomaps digital
elevation model. It seems that by the interpolation of the
contours digital elevation model has been generated. This DEM
represents only the terrain model and do not include the man
made features (or canopy). Description of DEM is as given
below:
Format: BIL+HDR
No. of Rows & Columns = 1301 & 1101
Pixel Size = 10m
Accuracy =1mrms
MAPUNITS: METERS
ULXMAP: 809000.00 m
ULYMAP: 1917000.00 m
2.2.2 DEM of Melbourne: Description of DEM is as given
below:
Projection Information:
Projection: UTM
Ellipsoid: WGS 84
Datum: WGS 84
Zone: 55 Southern hemisphere
Format: Tiff -TFW
No. of Rows & Columns = 360 & 320
Pixel Size =25 m
Accuracy = | m (Fraser, 2003)
MAPUNITS: METERS
ULXMAP: 315124.33 m
ULYMAP: 5816171.77 m
2.3 DIMAP Stereo Data Format: DIMAP stands for Digital
Image MAP. This data format has been introduced in mid-2002
for the launch of SPOTS satellite. DIMAP is a public-domain
format for describing geographic data. It is designed chiefly for
raster imagery, but it also supports vector data. DIMAP was
developed by SPOT Image in partnership with CNES (Centre
National d'Etudes Spatiales, France), the French space agency.
DIMAP is a two-part format comprising image data and
metadata.
Image data is by default in GeoTIFF format based on the
Tagged Image File Format (TIFF) that is the most widely used
today. This format is supported by all commercial software and
is therefore easy to integrate. The Geographic extension (Geo)
part of the format is supported by all GIS software packages.
The Geo part of GeoTIFF basically adds geo-referencing
information from the image file to the TIFF file (geographic
coordinates of the top-left corner and pixel sizes) and may also
specify the map projection and geodetic system.
In DIMAP, GeoTIFF data include all this information and map
projection codes are based on the EPSG (European Petroleum
Survey Group) geodetic parameters, which refer to the World
Geodetic System.
Metadata are in XML format (eXtensible Markup Language).
XML is like HTML, its structure being similar to HTML and it
allows users to create their own keywords and associated
values. Other advantages of XML are that it can be read directly
by standard Web browsers and supports stylesheets in XSL
(eXtensible Stylesheet Language) which transforms and
formats the information contained in an XML file.
2.4 DEM Format: The format of the reference DEM supplied
with the datasets is as follows:
Montmirail: The file DEM raster image format is binary (.bil)
with a metadata file named as header (.hdr).
Melbourne: The DEM raster image file format is Geotiff with a
tfw (tiff world) file. The tfw file contains the Upper left X and
Y co-ordinates and the pixel size of the image file for the user.
2.5 Control Point Data Format: An MS-Word document file
comprising 30 Ground control points has also been supplied
with the Melbourne datasets. The locations of the points have
been marked on IKONOS image clippings and their geographic
coordinates are given in a tabular form. The coordinates are
given both in WGS 84 geocentric as well as in UTM (WGS $4,
Zone: 55 S) projection. The accuracy of the GCPs is said to be
20 em (Fraser, 2003).
3. SOFTWARE USED TO EVALUATE
3.1 Saphire (Satellite photogrammetry software for Indian
remote sensing missions): Saphire has been developed at SAC
(Space Applications Centre), ISRO, Ahmedabad for DEM
generation from spaceborne stereo images. It was originally
developed for the stereo processing of IRS-IC/ID data.
Collinearity-condition equations form the basic model of the
software. Collinearity-condition states that the perspective
center, image point and the ground point are all in the same
straight line. The relationship between the image coordinates
and the corresponding ground coordinates is established through
the physical imaging model by way of a series of coordinate
transformations. This software was suitably modified to process
SPOTS HRS stereo images. See (Srivastava et al, 1996).
3.2 Geomatica: PCI Geomatica OrthoEngine version 9
software developed by PCI Geomatics, Canada was also used
for DEM generation. This software supports the DIMAP format
of SPOT images. This software supports reading of the image
data, ground-control-points (GCP) collection, geometric
modeling, DEM generation and editing, ortho-rectification, and
either manual or automatic mosaicking. The geometric model
used inside the software is a rigorous parametric model
developed by Dr. Toutin at the Canada Centre for Remote
Sensing (CCRS), Natural Resources Canada. This model is
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