Wednesday, April 8, 2009

Interactively convert SVY21 easting/northing coordinates to geographic latitude/longitude with Global Mapper 10

I'm trying out Global Mapper 10 to do coordinate conversion between SVY21 and geographic latitude and longitude coordinate systems. There is an interactive Coordinate Convertor available under the Global Mapper's Tools | Coordinate Convertor menu option. The Coordinate Convertor can convert between input and output coordinate systems with the option of zooming into the location and placing a point feature at the output location. To convert from SVY21 to geographic lat/lon coordinate system, here are the steps I took.
  1. Select Tools | Coordinate Convertor.

    The Coordinate Convertor dialog box appears.


  2. Click Select Input Projection. Note: this is where the parameters for the SVY21 projection are defined.

    The Select Input Projection dialog box appears.


  3. In the Projection drop down list, choose Transverse Mercator.
  4. In the Datum drop down list, choose WGS84.
  5. In the CENTRAL MERIDIAN parameter value field, enter 103.833333333333333.
    In the ORIGIN LATITUDE parameter value field, enter 1.366666666666666666667.
    In the FALSE EASTING (m) parameter value field, enter 28001.642.
    In the FALSE NORTHING (m) parameter value field, enter 38744.572.

  6. Click OK.

  7. Click Select Output Coordinate System.

    The Select Output Projection dialog box appears.


  8. In the Projection drop down list, choose Geographic (Latitude/Longitude).
  9. In the Datum drop down list, choose WGS84.
  10. In the Planar Units drop down list, choose ARC DEGREES.
  11. Click OK.
  12. Now enter the Input Coordinate X/Y SVY21 coordinates in the X/Easting and Y/Northing fields. For example, 24400 for X and 31600 for Y.

  13. Click Convert To.

    The Input coordinate is converted to the output coordinate. The message box below appears.

  14. Click OK.

    The Output Coordinate X/Longitude and Y/Latitude fields show the converted coordinates.


I compared the results with Intergraph GeoMedia and found the values are comparable. If you notice on the bottom right of the Coordinate Convertor dialog box, there are a couple of buttons - Center on Output Coordinates and Create New Point at Output Coordinates that you can use. I think it is obvious what they are used for. 

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