FANR5640/7640: Lecture 5 – Follow-up of Monday’s Photoscan lab


 

Follow-up of Monday’s Lab

Photoscan Workflow:

  • Add Photos
  • (Align Photos*)
  • Insert/Locate ground control points
  • Align Photos (again)
  • Build Dense Cloud
  • Build Mesh
  • Build DEM
  • Build Orthomosaic
  • Export DEM and Ortho

Problem with GPS Altitude EXIF tag lab data set:  Current Phantom 4 firmware populates the GPS Altitude tag with the GPS altitude – GPS altitude, as a rule of thumb, can exceed 3 to 4 times the horizontal error.

Solution:  Use the relative barometric altitude (luckily, the aircraft stores this measure in the EXIF, too).

The greater the altitude, the lower the pressure.  Over a short distance and period of time, this is considered a more-accurate measure of height above ground level (AGL).

EXIFTOOL

(Download Here)

Useage Examples:

List all EXIF tags for photo DJI_0186.JPG

exiftool.exe -s -g DJI_0186.JPG

Print the Relative Altitude of the photo DJI_0186.JPG:

exiftool.exe -p  $xmp:RelativeAltitude DJI_0186.JPG

Store the GPS Latitude, GPS Longitude, Relative Altitude of all photos beginning with "DJI" in a text file called headerinfo.txt:

exiftool.exe -T -FileName -GPSLatitude -GPSLongitude -xmp:RelativeAltitude DJI* > headerinfo.txt

Import this information into Photoscan

  • Process in Excel
  • Create a new Chunk, Import Photos, Import reference data from ‘Reference’ tab in Photoscan, …

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