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I'm pretty new to using GIS, but I've got two overlapping rasters of the same general area - one's a 1m resolution DEM from the Pennsylvania side, and the other's a 0.6m DEM resolution from the Maryland side. Both have their elevations measured in feet, but the elevations from the two DEMs in the overlapping areas are drastically different. Here's a screenshot from trying to display them on the same elevation scale: https://i.imgur.com/PgoNJwK.png

Here's the spatial reference information for the PA side:

Geodetic_Model:

    Horizontal_Datum_Name:North American Datum of 1983
    Ellipsoid_Name:Geodetic Reference System 80
    Semi-major_Axis:6378137.000000
    Denominator_of_Flattening_Ratio:298.257222

Vertical_Coordinate_System_Definition:

Altitude_System_Definition:

    Altitude_Datum_Name:North American Vertical Datum of 1988
    Altitude_Resolution:0.00000
    Altitude_Distance_Units:feet
    Altitude_Encoding_Method:Explicit elevation coordinate included with horizontal coordinates

And the corresponding CRS in QGIS for the PA side: +proj=lcc +lat_1=39.93333333333333 +lat_2=40.96666666666667 +lat_0=39.33333333333334 +lon_0=-77.75 +x_0=600000 +y_0=0 +datum=NAD83 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=us-ft +no_defs

And the MD side:

Geodetic_Model:

    Horizontal_Datum_Name:North American Datum of 1983
    Ellipsoid_Name:Geodetic Reference System 80
    Semi-major_Axis:6378137.000000
    Denominator_of_Flattening_Ratio:298.257

Vertical_Coordinate_System_Definition:

Altitude_System_Definition:

    Altitude_Datum_Name:North American Vertical Datum of 1988 (GEOID12A)
    Altitude_Resolution:0.0
    Altitude_Distance_Units:feet
    Altitude_Encoding_Method:Implicit coordinate

And the MD CRS: +proj=lcc +lat_1=39.45 +lat_2=38.3 +lat_0=37.66666666666666 +lon_0=-77 +x_0=399999.9999999999 +y_0=0 +datum=NAD83 +units=us-ft +no_defs

  • Is the difference between both raster constant along overlapping area? If yes, you can simply subtract or add the difference. But, both rasters are from the same source? It's weird to have a big difference – aldo_tapia Sep 25 '17 at 18:04
  • No, the two data sets are from different sources; each from their respective state and carried out independently. The differences in elevation appear to be about ~200 apart, but I'm not advanced enough to do a point by point analysis in the overlapping areas. – sverdrups Sep 25 '17 at 18:08
  • Altitude_Encoding_Method is different ... i wonder if elevation in southern raster is in meters. and the northern one in feet? have you tried using raster calculator to make a copy of southern raster, multiplying values by 3.28? – Steven Kay Sep 25 '17 at 18:28
  • ...yeah that was actually it. I can't believe I didn't try something that simple. Thanks a lot. – sverdrups Sep 25 '17 at 19:23
  • @StevenKay, you solved this question. Would you convert your comment as an answer? Let me know, and I will upvote it. Tks. – Andre Silva Mar 11 at 1:58

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