Orthorectification Practical

This practical is based on the orthorectification guide outlined in the ERDAS IMAGINE software manual (pp. 287-304). The work will help users to understand how to remove geometric distortion inherent in photographic imagery so that the corrected images will become suitable for further spatial processing and analyses. The first step in rectification will see the effects of camera orientation accounted for. Then the external effects brought by any relief displacement can be corrected by entering the elevation data, e.g. in the form of a digital elevation model (DEM).

In this practical, you are required to rectify a camera image of Palm Springs, CA, using a NAPP (National Aerial Photography Program) photo. The URL to the service at the time of writing is https://www.usgs.gov/centers/eros/science/usgs-eros-archive-aerial-photography-national-aerial-photography-program-napp. In the UK, the most comprehensive sources of data for academic users is offered by the Mimas Landmap service at http://learningzone.rspsoc.org.uk/.

The following basic steps in ERDAS IMAGINE are required to rectify a camera image:

• Display a camera image.
• Start the Geometric Correction Tool.
• Enter the Camera model properties.
• Record GCPs.
• Resample or calibrate the image.

When processing the data think of  the processes involved and information required to convert central perspective aerial photographs to orthophotos. Are the orthophotos suitable substitute for a traditional line maps ?

All data and instructions for this practical are available on Blackboard in the Practical materials Folder under the Course content tab.