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Precision product generation using satellite data and GPS based ground control points
Error Budget Analysis
The errors involved in each of the above-discussed methods of
generating precision products are as follows.
Digitizer based Method
- Inherent map accuracy
- Projection error
- Map-digitizer transformation error
- Image-map transformation error
Scanner based method
- Inherent map error
- Projection error
- Error in the tiling of reference maps
- Image-map transformation error
GPS based method
- GPS receiver positioning at the GCP
- Projection error
- Baseline accuracy
- Image-GCP transformation error
In the study, the IRS 1C LISS III data, with a spatial resolution
of 23 meters, is used to generate precision products on 1:50,000
scale. The error budget calculated in the study is presented in the
Table No.1
Advantages of GPS based GCPs
From the error budget analysis, it is clear that using GPS based GCP’s
will generate precision products with higher accuracy. The GPS
based GPC’s will be a direct input in image processing & GIS packages.
The GPS will also provide height information for each GCP.
The limitation of non availability of large scale reference
maps for generating precision products using high resolution satellite
data is easily overcome by using GPS based GCP’s. In addition to
this, the latest changes in the infrastructure are not reflected in the
reference maps which can be taken care by GPS.
Conclusions
The digitizer-based method is replaced by the scanner-based method
of georeferencing satellite data. The scanned reference map and the
satellite image can be directly accessed on to the screen side by side.
This will improve the identification of GCP’s more precisely.
The GPS technology which is emerged as powerful tool in
point positioning is readily adopted in Image processing & GIS
techniques for acquiring GCP’s. It will provide precise coordinates
of GCP’s. However, the coordinate information will be on WGS-84
datum for latlongs and ellipsoidal-based height measurements. This
coordinates has to be transformed into Everest ellipsoid using datum
transformation parameters. This task is not within the preview of
the present study.
References
- Lt. Col. (Dr.) B. Nagarajan, GPS for Large Scale Surveying,
Paper presented at the First National GPS Conference, IIT,
Kanpur, Feb.21-23, 1997
- Singh. S.K., Mohanta.B., and San Maung. U., Project Report
on Application of GPS in Pseudo Kinematic Mode, Survey
Training Institute, Survey Of India, Hyderabad, Aug., 1996
- Satellite Geodesy, Gunter Seeber, University of Hanover,
Germany, 1993
- Agarwal N.K., WGS 84 and GPS, Training Notes of “Special
Course on Geodesy, GPS and Photogrammetry for DOS/
ISRO Scientists” , Survey Training Institute, Survey Of
India, Hyderabad, Aug., 1996
- Integrated Study through Space Applications for Sustainable
Development, Regional Remote Sensing Service Centre,
Nagpur
- Methodology Manual for Preparation of Softcopy Precision
Products, Regional Remote Sensing Service Centre, Nagpur
- IRS 1C Data User’s Handbook, NDC, National Remote
Sensing Agency, Hyderabad
- Report of the Committed on “Map Proejctions and Datum
for Future IRS Data Products”, Space Application Center,
Ahmedabad
- Design of Map Projections for GIS data Integration at
State Level, Regional Remote Sensing Service Centre,
Nagpur
- Jan Van Sickle, PLS, GPS for Land Surveyors, Ann Arbor
Press, Inc., Chelsea, Michigan
- Lillesand, T.M. and Keifer, R.W. Remote Sensing and Image
Interpretation, 2 nd ed., John Wiley and Sons, New York,
1987
- Paul M.Mather, Computer processing of remotely sensed
images – An introduction, John Wiley Sons, 1987
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