GeodeticDatum.AuthoritativeAreaOfUseCode Method
Gives the code for the largest area of use for a geodetic datum.
AuthoritativeAreaOfUseCode(System.String datumAuthority, System.String datumAuthorityCode)
Gives the code for the largest area of use for a geodetic datum.Syntax
public static System.Int32 AuthoritativeAreaOfUseCode (
System.String datumAuthority,
System.String datumAuthorityCode
)Parameters
The name of an authority, usually epsg.
The unique code for the geodetic datum according to the authority, for example 6258.
Return Value
A code that identifies the largest area of use for the datum. Zero means unknown. If the value is 1024 or greater, it is an EPSG area code that can be used to look up an area polygon; see Remarks. If the code is positive but less than 1024, it is not an EPSG area code but an area code of the datumAuthority which could be "ESRI" or "IGNF"; such a code may not be very useful.
Remarks
The datumAuthority parameter must be "EPSG", "ESRI", "IGNF", "CRS" or "OGC". Carmenta methods will regard authority strings as case insensitive.
As for the output, the EPSG database represents each area in five ways:
a unique code (a number),
a short name,
a description that can be long,
a bounding rectangle expressed in WGS84/LongLat,
one or more polygons expressed in WGS84/LongLat.
This method returns the code (although it's not an EPSG code if less than 1024; see above).
There are other methods in this class that will directly give the name, description and bounding rectangle for the largest area of use. But to find the polygons, you must first find the code, and then use it to look up the polygon in a shapefile published by EPSG: in the menu EPSG Dataset, choose Download Dataset, then you find the area polygons under the EPSG supporting files heading. The polygon attribute to look up is called ExtentCode. So, download the shapefile and make a ShapefileDataSet from it. If, for example, you have an area code of 1298 (which represents the area Europe - ETRF by country), you can get the area polygons by calling DataSet.GetFeatures(featureQuery), where the FeatureQuery.Condition is
ExtentCode = 1298
The area of use for a geodetic datum is not always unique. Before version 10.003, the EPSG database assigned each geodetic datum and each CRS a single Area of Use. Since version 10.003, each geodetic datum and each CRS instead gets a Usage (a way of using it), and each usage refers to an Extent and a Scope, so nowadays, the usage extent corresponds to the old area of use. And in rare cases, an entity can get several alternative usages with different extents and scopes. For example, the old Swedish Grid, EPSG:3021, has a countrywide extent for the scope of medium and small scale mapping, and also a more narrow extent, near the central meridian where the projection distortions are minimal, for the scope of large scale (detailed) mapping. When there is more than one usage extent, this method will return the code for the largest one.
Platforms
Windows, Linux, Android