DatumShiftInfo Class
Contains documentation for a DatumShift, like accuracy and area of use.
NuGet/Assembly: Carmenta.Engine.5.16.2.nupkg (in the CECore assembly)
Syntax
public class DatumShiftInfo : ResourceObjectRemarks
A DatumShiftInfo documents a datum shift, and is usually a component of the datum shift. The component can be supplied manually as an argument to a datum shift constructor, or it can be created automatically, for example when a Crs is extracted from dataset files.
It is not necessary to give a DatumShiftInfo when you construct a datum shift. If you have specified the DatumShift.Authority and DatumShift.AuthorityCode , Carmenta Engine can usually generate the DatumShiftInfo automatically if needed.
However, if you call GeodeticDatum.AlternativeDatumShifts or GeodeticDatum.AlternativeDatumShiftsForArea, you will get a collection of free-floating DatumShiftInfo instances that are not attached to any datum shift. When you have chosen the DatumShiftInfo you like, you can construct the corresponding datum shift from it. (If the datum shift is a GridFileDatumShift, its construction will succeed only if the FileStatus says that at least one grid file can be found.)
See also Can I read the CRS from file, and just assign the datum shift manually?
When you use Carmenta Explorer to display a dataset whose Crs is not based on WGS84, you can see information from the DatumShiftInfo in the Properties window when you have selected the dataset in the DataSets window.
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Above, the CRS of the LandUseTIFF is based on NAD27 (North American Datum 1927), and we can see that Carmenta has been configured to use a simple 3-parameter Helmert datum shift from NAD27 to WGS84, which is intended for CONUS (Contiguous U.S.) and has about 10 m accuracy there. (For this datum shift, the accuracy in various areas is displayed in more detail here.)
Area of Use
The area of use for a datum shift can be smaller than the area of use for the geodetic datum, because one can construct more accurate datum shifts by restricting their area of use.
It can be risky to use a datum shift outside its area of use, since the accuracy cannot be predicted. One of the worst surprises comes from the Japanese datum shift EPSG:15483, "Tokyo to JGD2000 (1)". Its accuracy is 9 meters on the main islands, but EPSG mentions five groups of remote islands where the accuracy is 793 m, 642 m, 560 m, 251 m and 248 m.
A DatumShiftInfo instance stores the area of use in different forms:
AreaOfUseCode is a code number, which can be used to look up the area polygon(s) in a shapefile published by EPSG.
AreaOfUseName is a short name, appropriate in list of alternative instances of DatumShiftInfo.
AreaOfUseDescription is a description that can be longer, useful for text search.
AreaOfUseBounds is a bounding rectangle (or two) expressed in Wgs84LongLat.
The AreaOfUseBounds cannot be specified when you construct a DatumShiftInfo manually in Carmenta Studio, but it will be initialized when a DatumShiftInfo is constructed automatically.
Inheritance Hierarchy
System.Object (not available in C#)
EngineObject
ResourceObject
DatumShiftInfo
Platforms
Windows, Linux, Android
DatumShiftInfo Members
The DatumShiftInfo type has the following members.
Properties
| Name | Description |
|---|---|
| Accuracy | Gets the accuracy of the datum shift (in the area of use). |
| AreaOfUseBounds | Gets bounding rectangles for the area of use for the datum shift. |
| AreaOfUseCode | Gets the EPSG code for the area of use for the datum shift. |
| AreaOfUseDescription | Gets a (possibly long) description of the area of use for the datum shift. |
| AreaOfUseName | Gets a short name for the area of use for the datum shift. |
| Authority | Gets the name of an authority, which is often "epsg". |
| AuthorityCode | Gets the unique code for the datum shift instance, according to the Authority, for example "15978". |
| FileStatus | Gets the file status (missing or found) for one or more grid shift files (NTv2 or CTable). |
| InformationSource | Gets the original information source for the datum shift. |
| IsDisposed | Gets a value that tells whether the current DatumShiftInfo has been disposed. Inherited from EngineObject |
| Name | Gets or sets the name of the DatumShiftInfo. Inherited from ResourceObject |
| NativeHandle | Gets the native Carmenta Engine kernel object the current DatumShiftInfo represents. Inherited from EngineObject |
| OriginalAccuracy | Gets the original accuracy of the datum shift (in the area of use). |
| Path | Gets the path to a directory containing one or more grid shift files (NTv2 or CTable). |
| Remarks | Gets the remarks for the datum shift. |
| Scope | Gets the scope (usage and applicability) of the datum shift. |
| Type | Gets a description of the type of the datum shift. |
| IUserProperties.UserProperties | Gets the AttributeSet that contains the user properties. Inherited from IUserProperties |
Methods
| Name | Description |
|---|---|
| Clone | Creates a copy of an object. Inherited from EngineObject |
| Dispose | Releases the reference to the native Carmenta Engine kernel instance the EngineObject represents. Inherited from EngineObject |
| Equals | Determines whether this instance is equal to another. Inherited from EngineObject |