When I am doing georeferencing in Context Capture, the field of Z value is named "Given Ellipsoidal height". What should I put into this field? If I collect my data by GPS or Traditional Survey, any pre-process required? Thanks
Hi Ben,
Please refer to the ContextCapture user manual page 244:
"ContextCapture describes georeferenced positions using two geographic (longitude, latitude) or two projected (X, Y) coordinates, complemented with ellipsoidal height, which is the height above the reference ellipsoid (usually WGS84, but it may be a different ellipsoid, e.g. GRS80, for some spatial reference systems). Ellipsoid height differs from orthometric height, which is closer to the popular height above sea level.
ContextCapture uses ellipsoidal height instead of orthometric height, because the former has a simple and unambiguous mathematical definition, whereas the latter is based on a geoid height grid subject to sampling and accuracy issues."
Answer Verified By: Ben Nion
Thanks Felix
I understand why ContextCaptur uses ellipsoidal height. But if I use orthometric height (limited to the data source), how much the differences can be? Or any method can find that differences? For better understanding, please use Hong Kong as an example.
Thanks
Ellipsoidal or geoid is the reference level above which the height is measured.
So there can be a major difference (which is not constant) between these values. It is the user’s role to know in which system the Z-values are proposed.