Monday, September 5, 2011

Google Maps tool for creating air photo frames

In aerial digital photography, the area captured by the camera is dependent on a number of factors including the camera lens and sensor dimensions, the flying speed and height, and the capture interval. For instance, if the capture interval is too slow and the aircraft is flying too fast, the amount of overlap between photo frames could be less and there could be gaps in coverage. The pixel ground resolution is also a consideration. With this tool , it is possible to estimate the coverage, overlap, resolution, given certain input parameters prior to the actual survey mission.

This Google Maps based tool was written partly based on some information about calculating camera field of views from this site http://www.bobatkins.com/photography/technical/field_of_view.html. The tool also use geodetic functions by Chris Veness from www.movable-type.co.uk/scripts/latlong.html.

The command makes a few assumptions:
  1. The camera sensor is a full frame sensor
  2. There is no lens distortion
  3. The ground elevation is flat and is based on the elevation at the center of the frame
  4. The earth is a perfect spheroid
  5. There is no roll and pitch.
The tool makes use of the Google Elevations Service to obtain the ground elevations at the center of the photo frames.

To use this tool,
  1. Click this link http://dominoc925-pages.appspot.com/mapplets/camframes.html.
  2. Fill in the camera focal length e.g. 50
  3. Fill in the camera sensor width e.g. 59.
  4. Fill in the camera sensor height e.g. 36.7.
  5. Fill in the camera sensor horizontal pixel dimensions e.g. 8176.
  6. Fill in the camera sensor vertical pixel dimensions e.g. 6132.
  7. Enter the aircraft altitude e.g. 1080.
  8. Enter the initial latitude and longitude position of the aircraft, e.g. 33.7232 and -100.3347.
  9. Set the capture interval e.g. 6.
  10. Enter the aircraft speed e.g. 33
  11. Enter the aircraft bearing e.g. 10
  12. Enter the number of frames to create e.g. 10.
  13. Click the Create button.

    The frames are created.
 To create a KML file, simply click the KML button. Then click the text area below the settings and press CTRL+C to copy the text to the clipboard. Then open up a text editor and paste the contents inside. Save the file with a .KML extension.

An example of the file in Google Earth is displayed in the screen shot below.

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