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KAP GPS

In the last month I have been using the PowerShot S100 on a lot of KAP flights with the Saturn V Rig. The S100 has an integrated GPS receiver and I have been using that to write the GPS coordinates to each photo captured. I finally got around to using the GPS data after two recent flights. When I crashed the rig I wanted to see if the altitude data documented how fast the camera descended. Then I tried to visualize where the camera was when it took KAP photos of Bristol, VT. The video below describes the effort over Bristol.

There are different workflows for using this GPS data. The one I used can be done with free software, although the video above was made with Adobe Premiere.

The basics steps I used are:

1)      Camera: Turn on the GPS to save data with each photo.

2)      Extract GPS data: Use ExifTool to extract longitude, latitude, and altitude from all the jpegs in a directory and produce a text file.

3)      Decimal degrees: Use a spreadsheet program to change the degree:minute:second format to decimal degrees, crop the data file if desired, and output a comma separated file.

4)      KML: Transform the comma separated LON,LAT,ALT  file into a KML file that Google Earth can read.

5)      Visualize the data: Open the KML in Google Earth to see where the camera was. Use the “fly around” tools in Google Earth to animate the visualization and record a video of it.

6)      Make a movie: Put the video files together into a story.

Some details about these steps:

1)      Camera: The S100 has two GPS options. “GPS” writes the location data into each jpeg saved. I don’t know how this works if you are saving RAW files instead of jpegs. The other option is “GPS Logger” which makes a separate file of GPS coordinates. I have not used this and I don’t know how often it saves the data or whether it even works when CHDK is being used and the SD card is locked.

2)      ExifTool: Download the free ExifTool. When the jpeg files from a session with the S100 are in a directory on your computer, run ExifTool from the command prompt with a command like this:

C:\>exiftool –csv –filename –gps:GPSLongitude –gps:GPSLatitude –gps:GPSAltitude –gps:GPSTimeStamp ./yourdirectory >youroutputfile.csv

The above assumes that your system can find the exiftool.exe program (or that it is in the C:\ root directory). It also assumes that “yourdirectory” where the jpeg files are is a directory of C:\. It also assumes that “exiftool.exe” is the name of ExifTool which might be installed as “exiftool(-k).exe” (which you should just rename to “exiftool.exe”). This command makes a comma separated text file with the filename, longitude, latitude, altitude, and time for each photo.

3)      Decimal degrees: I used Excel to change the degree:minute:second format (e.g., 73 deg 4' 26.31") into decimal degrees (e.g., -73.073975). First use Text to Columns to get the 73, the 4, and the 26.31 into separate columns. Then use a formula like =-(degrees+(minutes/60)+(seconds/3600)). The altitude data need to have the “m” for meter removed (use Text to Columns). Output a csv file with just the Lon, Lat, and Alt results.

4)      Make a KML file: A KML file is a text file with some HTML-like stuff at the beginning and end. The data you want in the middle is just your comma separated Lon, Lat, Alt file. So to transform your csv file into a KML file you can just copy in the header and footer from another KML file. Try this KML file: Sample KML file. Paste in the header and footer and change the YourFileName.kml and the YourFileName to a useful filename. Save it as plain text.

5)      Visualize the data: Your KML file should open in Google Earth and display the GPS data. Google Earth allows you to change the color and thickness of the lines that are the traces connecting the GPS coordinates. If you want segments of the trace to be a different color, you can make separate KML files for each segment (or learn more about KML than I know). To fly around like I did in the video above, I drew a path (with the Path tool) that was an arc. In the Places sidebar, select a path and click the “Play Tour” button below. As you fly along the path, hold the mouse where you want the “camera” to point. To record your flight, click the “Record a Tour” button (top row of icons) and then save it when you get a good flight. To record that saved tour as a video, select Tools/Movie Maker (only in Google Earth Pro, which is now free). I used WMV9 (16mbps) at 1280x720 resolution. The saved videos don’t look as good as the live animation in Google Earth, but it’s all you get.

6)      Make a movie: The video files made in Google Earth can be edited in any video editing program.

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