|
Fast Orthophoto Production using the Digital Sensor System
To analyse the accuracy of the produced orthophoto, a number
of the checkpoints were measured on the resulting orthomosaic
and compared to the land-surveyed coordinates. The statistics
of the checkpoint residuals with respect to individual terrain
and overall test area are presented in Table 7.
Examining the results in Table 7, it is obvious that the checkpoint accuracy is better than 0.5 meter in all terrain areas. Note that more than 10 checkpoints have been used in each terrain area and they vary from parking lot lines, sidewalk curbs to driveway corners, etc. Table 8 represents the orthophoto horizontal accuracy requirement from The United States Geological Survey (USGS).
Using the aforementioned horizontal accuracy requirements listed in Table 8 and the DSS-derived orthophoto accuracy presented in Table 7, it is clear that the orthomosaic generated from this DSS test flight data presented here can be resampled up to a map scale 1: 600. This has proven that fast orthophoto production using DSS data fits various mapping standards, with minimum operator interaction during the process. 7. Conclusions The Digital Sensor System (DSS) has been used to collect airborne digital images and their associated direct georeferencing data over Southern Ontario, Canada to evaluate the performance of the DSS for Fast Orthophoto production. A subset of the images collected in the Southern Ontario Flight (flown over Ajax) has been used to analyse the calibration and quality control procedure developed by Applanix for the DSS. ISAT has been used to automatically collect tie points in the imagery and then POSCal has been used to calibrate the individual system components and the system as a whole. The airborne calibrated parameters (using only one control point) have been introduced to ISAT once more to perform an independent check of the checkpoint analysis using the EO Analysis capability of ISAT software. The results of such analysis is presented in some detail and confirmed the validity of the calibration and quality control procedure and tools developed for the DSS. The DSS digital imagery along with their associated POS-derived exterior orientation parameters were then used to extract a Digital Elevation Model of the Ajax area. The semi automatically extracted DEM has been used to generate an orthophoto mosaic of the same area. The DEM extraction and Orthophoto mosaic generation have been produced using ERDAS Imagine, with minimal operator interaction. The resulting Orthophoto mosaic was evaluated using checkpoint residual analysis and the results of such analysis are presented in some detail. Of final note: the orthophoto presented in this paper was produced in a matter of days, including data acquisition., In addition, the orthophoto generated by the DSS self-extracted DEM contains the most up-to-date terrain information, which is especially useful for GIS database update in which re/developing areas are of interest. Finally, the real-time navigation solution provided by the POS AV system could be used to produce a near real-time orthophoto using an existing DEM, such as from the USGS. This is very useful in rapid response applications such as fire and hazard monitoring or protection. 8. Acknowedgements Financial Support of the first author has been partially provided by The University of Calgary, The National Sciences and Engineering Research Council of Canada (NSERC) and by Applanix Corporation. Z/I Imaging Corporation has provided the ISAT software which has been used in the automated tie point generation and EO analysis used in this research. Leica Geosystems provided the ERDAS Imagine software which has been used for the DEM generation and orthophoto production used in the presented analysis. Aircraft and Crew were provided by The Airborne Sensing Corporation, Toronto, Canada. Thanks to Joe Hutton, Greg Lipa, and Ernest Yap of Applanix Corporation for their cooperation during data acquisition, processing and analysis. 9. References
Page 3 of 3
| Previous | |