Photogrammetric Mapping

Discussions

For stereo compilation, the Analytical plotter is a clear winner. For largescale mapping, softcopy systems couldn’t resolve the ?ner details that Analytical plotters could do.Through observation it has been found that Analytical systems give better accuracy up to 5-10 cms whereas digital systems give an accuracy of 09-13 cms. Since diapositive has continuous tone so it doesn’t get blurred while zooming and gives better view and results whereas digital images can’t give the same results as these are having pixel. The size of the pixel of these images depends on the scanning (DPI) and resolution of Photographs. If one image has a pixel size of 14 microns (Scale 1:10000) and other image has pixel size of 24 microns (Scale 1:10000) than we would get better accuracy with the image having pixel of 14-micron size. That means if the resolution were better, the accuracy would be better.

With regards to Image Quality the vote went in favour of the Analytical plotters although several users said that the difference, particularly on the higher resolution (15 microns) was not that great.

For DEM generation, there is a positive feeling amongst users that softcopy system are as accurate or better than Analytical plotter and that correlation gave the softcopy system a distinct advantage.

Aerial triangulation is also an area where the softcopy system performed well and many users stated that they achieved faster and easier production. If the only function of softcopy was stereo plotting, it appears that their impact would be considerably less than we are experiencing. However, the softcopy systems are more in use and covers in many areas of map production in a single system.

Through softcopy systems, one has the option for number of applications, all in the same environment (compilation, DEM, draping of contours, orthogenertion etc.) and softcopy systems are less expensive.

Results

Evaluated the accuracy of orientation parameters as well as the quality of datasets of analytical and digital systems. Also checked the data accuracy obtained through images with a pixel size of 14 microns and 24 microns. Dataset from 24 microns per pixel is of inferior quality.

Production Accuracy

From accuracy point of views, for stereo plotiing, Analytical Plotters give better accuracy as compared to Digital Workstations. Regarding DTM generation, softcopy can be considered better.

Conclusion

In Photogrammetry, aerial data is being used for Mapping and Up gradation of urban sprawl. Both digital and analytical techniques offer potential for those interested in recording surface features. However, selection of the technique needs to be based on a careful consideration of the end products required. In general, this research shows that digital photogrammetry performs well but comparative analysis of Analytical and digital dataset, on the basis of equal resolution, shows that analytical instrument give a better planimetric and altimetric (Z-value) accuracy than Digital workstations.

At present, both analytical and digital systems offer solutions for utility mapping and research. However, as shown in this case study, the digital data capture systems can’t compete on accuracy terms with analytical systems but offer many potential advantages in terms of data collection time and other end products, which are available. However, despite the increasing user friendliness of many of the digital systems, a high level of expertise is still required.

References:

1 Text Book of Photogrammetry, P.R Wolf

2 Manual of Photogrammetry, American Society of Photogrammetry, Fourth Edition

3 State of the Art of Digital Photogrammetric Workstations for Topographic Applications, C.Helpke,Photogrammetric Engineering & Remote Sensing ,Vol.61,No.1,Jan1995,pp49-56

4 IIRS-1C/Dstereo Data Processing System-Operartion Manual for DEM and Orthoimage Product Generation Software (Dat Version) for IRS1C/D, Signal and Image Processing Group, Signal, Image and Information Processing area, SAC, Ahemdabad.

5 Concepts and Algorithms in Digital Photogrammetry,by T.Schenk,OEEPE Journal,Vol.49, No.6,Dec.1994

6 Earth Surf, Process. Landforms 28, 307–320 (2003)

7 Proceedings : Mapping and Remote Sensing Tools for the 21st Century, conference and exposition with feature emphasis on Public / Private Interaction, august 26-29, 1994, Washington D.C.