Is it possible to use GPS geographic coordinates & ellipsoidal height not orthometric heights in Aerial Triangulation?

  • Do you have a geoid raster? You can convert them to orthometric – aldo_tapia Mar 26 '18 at 19:12
  • Ellipsoidal heights aren't necessarily related to the topography, so I would say, no. – mkennedy Mar 26 '18 at 21:58

In the context of structure-from-motion (SFM) photogrammetry - using ellipsoid heights for aerial triangulation is preferred because the ellipsoid is a mathematical model and this makes computations straightforward. This is especially so if your survey area is large. You can always output your results later in orthometric heights. In my experience, many SFM photogrammetry software gets the aerial triangulation wrong when given orthometric heights especially over a large area.

Capture your source data in ellipsoidal heights. Take/apply as many ground control points as you can - which also must be in ellipsoidal heights. After aerial triangulation, and "model generation", and when you want to output the result (eg DSM) - this is where you apply the geoid undulation layer, which is usually supplied in a grid file.

Of course SFM can only output DSM (which includes heights of man-made structures) and not DTM (which excludes man-made structures). For DTM, you need LIDAR processes, but they are no longer photogrammetry although the LIDAR outputs are often used as inputs for "adjusting" aerial maps.

  • At what stage need convertion from ellipsoidal to orthometric before vector data capturing & DTM generation? – Shahid Mar 27 '18 at 4:33
  • Is it possible to capture vector data in ellipsoidal height? Or convert first E-height to orthometric by using geoid grid and than captured vector data in stereo environment. – Shahid Mar 27 '18 at 8:56
  • As an example, the Vexcel cameras capture positions in WGS84 ellipsoid heights.(vexcel-imaging.com). This is also the case with drones with onboard GNSS functionality. – Ralph Tee Mar 27 '18 at 9:35
  • But are GPS-derived heights accurate enough? – Martin F Sep 15 '18 at 19:43
  • @MartinF If "GPS-derived heights" meant uncorrected/undifferentiated autonomous positions - then of course it is a 'no' for survey-accurate outputs. – Ralph Tee Sep 17 '18 at 20:20

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