Reprojector Class

The Reprojector class handles conversion from a source map projection to a target map projection. The conversion can be performed with or without height. The conversion automatically handles datum (ellipsoid) conversions, and can also perform datum shifts.

The TypeOfConversion defines type of coordinates used in conversion.

The reprojection conversion from source map projection to target map projection coordinates works as follows:

• Source projection coordinates (east, north) are converted to source geographic coordinates (lon, lat)
• Source geographic coordinates (lon, lat, height) are converted to source Eucledian datum coordinates (x,y,z)
• Datum shift is applied, if specified, to target Eucledian datum coordinates (x,y,z)
• Target Eucledian datum coordinates (x,y,z) are converted to target geographic coordinates (lon, lat, height)
• Target geographic coordinates (lon, lat) are converted to target projection coordinates (east, north)

When datum shift parameters are not specified, and the datums (ellipsoids) of the source and the target are identical, the three middel steps are skipped. The three middle steps can also be bypassed by setting explicitly the BypassDatumConversions property to false. That will give incorrect results, however especially some graphical tools does this for performance reasons: Visually the results will look ok as long as all data are defined in projections sharing the same datum (ellipsoid), and all visualization take place in target projection - if data are defined in projections using different datums (ellipsoids), errors will occur.

The datum shift works in a two step process:

• Source datum shift conversion is applied, if specified
• Target datum shift inverse conversion is applied, if specified

It is possible to specify datum shift parameters for as well the source as the target map projection.

If datum shift parameters directly from source to target is known, this must be set as the source datum shift parameters.

If datum shift parameters directly from target to source is known, this must be set as the target datum shift parameters.

If datum shift parameters is known from both source and target to a common datum, both set of parameters must be specified. Then a reprojection will first convert from source datum to common datum, and then from common datum to target datum by an inverse datum shift operation.

public class Reprojector

Public Class Reprojector

public ref class Reprojector

type Reprojector =  class end

// Projection strings are truncated due to their lenghts.
string utm20NNad1927 = @"PROJCS[""NAD_1927_UTM_Zone_20N"", ... 
string utm20NWgs84 = @"PROJCS[""WGS_1984_UTM_Zone_20N"", ... 

// Create reprojector.
Reprojector reprojector = new Reprojector(utm20NNad1927, utm20NWgs84);

// Conversion from projection-to-projection coordinates, no height
x = 35000; y = 6000000;
reprojector.Convert(ref x, ref y);

// Converting from projection-to-geographical coordiantes, including height
reprojector.TypeOfConversion = Reprojector.ConversionType.Proj2Geo;
x = 35000; y = 6000000; h = 100;
reprojector.Convert(ref x, ref y, ref h);