With this Datum transformation parameters wizard, you can find geodetic datum transformation parameters between the coordinate systems of two point maps, where:
the coordinate system of the first point map is supposed to use a local (unknown) geodetic datum,
the coordinate system of the second point map is supposed to use a global geodetic datum, preferably WGS 84.
Optionally, you can specify height columns containing the height values of the points in the input point maps.
You can choose to use one of the following calculation methods:
Geo-centric datum shift
Molodensky
Bursa Wolf
Molodensky Badekas
Optionally, you can save the calculated transformation parameters in the coordinate system of the first point map.
The datum of the first coordinate system will then be changed.
The first coordinate system will then be compatible with the WGS 84 datum, and thus with any other known datum.
Automatic coordinate transformations during display etc. are then possible for any map that uses the first coordinate system.
Purpose of this page:
On this first page of the wizard, you should select two input point maps, each containing a set of common control points. For each point map, you can optionally select a column containing the height values for that set of control points.
Dialog box options:
Point map with local datum:
Select the first input point map. Open the list box and select the desired point map.
The first coordinate system is supposed to use a local datum.
The aim of the wizard is to enable a transformation between the coordinate system with this local datum (1st point map) to the global WGS 84 datum (2nd point map), and thus enable transformations to any other datum.
Use heights (m):
Select this check box to include the height values of the points in the first point map.
From an attribute table of the first point map, select a column that contains height values for the points.
The height values are supposed to be specified in meters above the ellipsoid. For instance, for the Dutch RD datum, height values are relative to NAP, and corrected for geoid-ellipsoid separation.
Clear this check box when you do not wish to include height values for the first set of control points.
This second point map must use the sameID domain as the first point map. The control points are common points: 'Point 1' in the first map must refer to 'Point 1' in the second point map, etc.; the wizard will compare the locations of the points in the two point maps to each other.
The coordinate system of the second point map is supposed to use a globally defined datum.
When you wish to save calculated transformation parameters later on, the second point map must use a coordinate system that uses the WGS 84 datum.
Use heights (m):
Select this check box to include the height values of the points in the second point map.
From an attribute table of the second point map, select a column that contains height values for the points.
The height values are supposed to be specified in meters above the ellipsoid, as used by the coordinate system of the second point map.
Clear this check box when you do not wish to include height values for the second set of control points.
For your information, the page lists for each point map:
the number of points in the map,
the coordinate system of the map, and
the coordinate system's ellipsoid,
the coordinate system's datum.
When finished selecting the two sets of control points (the two point maps and their optional height columns), you can click the Next button and continue on the Method page.