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I'm very new to GIS so here my question is I have WGS84 DEM data for my country and I want to calculate the sea level rise.

I will use QGIS raster calculator, my problem is I need to find sea level for WGS84 datum or the reverse my vertical datum will be the mean sea level?

Any solution?

  • What is the vertical datum of your DEM? Also, in which context are you calculating this? Is it for a cartographic simulation of sea level rise? – FSimardGIS Dec 12 '18 at 2:04
  • I think WGS 84 is already a vdatum and my purpose is the same as you said. – k112 Dec 12 '18 at 13:01
  • I suggest you verify an known elevation in your DEM to see if it matches ellipsoidal heights or elevations above sea level. If they actually match ellipsoidal heights, then you'll have to subtract geoid heights from them, from EGM2008 or a local geoid. If they match elevations AMSL, then for your purpose (a country-wide simulation), I think it would be correct to execute your simulation directly. – FSimardGIS Dec 12 '18 at 15:11
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You can download the differences between the WGS 84 spheriod and the Earth Gravitation Model 2008 (EGM2008) in an ESRI grid format here:

http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008/egm08_gis.html

The value in each cell is the amount you need to add or subtract from the WGS 84 elevation to get the geoid (sea level) elevation.

Disclaimer: I'm not an expert in geodesy, so any corrections or further explanations are welcome.

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    True, however, most DEMs are already referenced to a specific vertical datum. I doubt that any proper DEM would be showing ellipsoidal heights, because such a DEM wouldn't be "Analysis Ready". That said, it is not impossible either. I asked the OP for more details as well. – FSimardGIS Dec 12 '18 at 2:14

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