Questions tagged [geoid]

The hypothetical, natural, surface of mean sea level for the whole Earth. An equipotential gravitational surface. The datum for orthometric heights.

26
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3answers
1k views

Are ellipsoids a mathematical necessity?

The literature usually just tells us that the Geoid is too complex to describe mathematically and that we therefore fit different Ellipsoids to approximate it. Are these Ellipsoids mathematically ...
7
votes
4answers
789 views

How does a Spatial Reference System like WGS84 have an elipsoid and a geoid?

I found out that WGS84 is an ellipsoid with a "geoid component", but I'm unsure exactly how that can be. This is from PostGIS in Action, Second Edition (pg. 64), but it seemed a bit vague. ...
6
votes
2answers
359 views

Are LiDAR datasets with same vertical datum, but based on different geoids comparable?

I have two sets of LiDAR for the same region that I would like to compare. Both are in NAVD88. The older LiDAR set used GEOID03 for the transformation. The newer LiDAR set used GEOID09 for the ...
3
votes
2answers
2k views

How to convert the SRTM DEM orthometric to ellipsoidal heights using ArcGIS or others GIS?

Recently I got the SRTM DEM from Cgiar,which based on WGS84/EGM96. and I merged the tiles to one tiff file. I want to get the WGS84 ellipsoidal heights. According the steps from the Arcgis Help 10.2 ...
3
votes
2answers
2k views

How do you convert SRTM HGT elevations from WGS84 into meters above sea level?

I am building a JavaScript script that reads binary HGT files - as generated by the SRTM - and converts the data into bitmaps viewable in your browser. You can try out the script and view the source ...
3
votes
4answers
3k views

“Horizontal” and vertical datums terminology

I have heard people referring to as a horizontal datum to models such as WGS84 and as a vertical datum to geoids. The former is primarily used for determining latitude and longitude but also the ...
2
votes
0answers
710 views

Correcting incorrect altitudes of points recorded by my Android or how to calculate Geoid Height in QGIS

I tried to edit my question with more details and I also think that lot of people can benefit from this question! I was recording a track with my Android and later I found out that I end up having ...