GeoTools
  1. GeoTools
  2. GEOT-3813

Bug in the javadocs for VerticalTransform and ModifiedEarthGravitationalModel

    Details

    • Type: Bug Bug
    • Status: Open Open
    • Priority: Major Major
    • Resolution: Unresolved
    • Affects Version/s: 2.7.2
    • Fix Version/s: None
    • Component/s: docs, referencing3D
    • Labels:
      None
    • Environment:
      Using trunk of geotools. Affects all operating systems, java versions, and hardware platforms.

      Description

      The javadocs for VerticalTransform and ModifiedEarthGravitationalModel heightOffset state this:

      Returns the value to add to a <cite>height above the ellipsoid</cite> in order to get a <cite>height above the geoid</cite> for the specified geographic coordinate.

      I believe this is exactly the opposite. As you can see here:

      http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/intpthel.html

      WGS 84 Ellipsoid height = Orthometric height + EGM96 Geoid height

      In other words, the javadocs should probably read this:

      "Returns the value to add to a <cite>height above the geoid</cite> in order to get a <cite>height above the ellipsoid</cite> for the specified geographic coordinate."

      Or this:

      "Returns the value to subtract from a <cite>height above the ellipsoid</cite> in order to get a <cite>height above the geoid</cite> for the specified geographic coordinate."

      But if I follow the javadocs's suggestion, I get a value that is very wrong.

      Example:
      Here is: 38.883,-77.106
      The DTED0 HAE for here is: 56 meters
      The DTED0 Height above Geoid for here is: 89 meters
      The heightOffset is returning: -33 meters

      So, I can take the HAE and subtract the heightOffset to get the height above Geoid.
      Or, I can take the height above geoid and add the heightOffset to get the HAE.
      But I CANNOT take the HAE and ADD the heightOffset to get the height above Geoid.

      Also affects:

      • Geotoolkit
      • The rest of the VerticalTransform class (I see addition being used to convert from HAE to Height above Geoid)

      Thank you for your attention!

      adrian

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          People

          • Assignee:
            Jody Garnett
            Reporter:
            arichnad
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            Dates

            • Created:
              Updated: