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How does Pix4D generate/calculate the elevation Z value?

I’ve used Pix4d Capture on several projects to create a 3d model, including DSM. The elevation values in the DSM seem to be way off of reality.

IE, I did a flight mission at the beach, and the DSM indicated that my elevation was -18 ft at the water’s edge. 

So, I’m wondering how the Pix4d software generates the elevation data in the DSM–Does it pull information from the drone’s GPS’s sensors during the flight? Is it calculating Z based based on something else? 

Thank you, 

HI Lael,

Pix4D uses data in the Image EXIF files (taken from the drones or associated digital camera of choice).  The Drone GPS does not record data related to Mean Sea Level, but rather the Height above the Ellipsoid.  There can be a significant difference between a GPS ellipsoid height and mean sea level. Pix4D can process images with no geotag data, however the resulting project will come out as an Arbitrary Coordinate system and not have accurate scale/orientation.  It is strongly encouraged to establish accurate Ground Control Points in a project for the highest levels of accuracy.

Regards,

Aaron Woods