Grid shift files facilitate transformation from one coordinate reference system to another. A grid shift file is often used for defining a transformation over an area when a higher accuracy transformation is required.
Some common transformations with identifiers are listed in the table below:
DatumTxID | Area of Use | Coordinate Reference System | Coordinate Reference System ID | Method | Grid Shift File(s) |
|---|---|---|---|---|---|
RDNAP | Holland | RD New+NAP height | EPSG:7415 | RDNAPTRANS™ |
|
NTFRFG93_4807 | France | NTF (Paris) | EPSG:4807 | NTv2 |
|
NTFRFG93_4275 | France | NTF | EPSG:4275 | NTv2 |
|
EPSG:15956 | UK | OSGB 1936 / British National Grid | EPSG:27700 | OSTN |
|
EPSG:15864 | US (Alaska) | NAD27 | EPSG:4267 | NADCON |
|
EPSG:15851 | US | NAD27 | EPSG:4267 | NADCON |
|
EPSG:15786 | Australia | AGD66 | EPSG:4202 | NTv2 |
|
EPSG:5339 | UK | OSGB 1936 | EPSG:4277 | NTv2 |
|
EPSG:1693 | Canada | NAD27 | EPSG:4267 | NTv2 |
|
HPD is installed with the following grid shift files:
• .las and .los files for the NADCON transformations from NAD27 (US)
• .grd files for the RDNAPTRANS™ transformation from RDNap (Netherlands)
• .txt file for the OSTN transformation from OSGB36 (UK)
Grid shift files from a third-party can be added.
1. Copy the system\Gridshifts folder to another location.
2. Copy the new grid shift files to the new Gridshifts folder
3. Copy the boundcrs.dat file to the new folder.
4. Start an HPD editor.
5. Select Tools > Options and change Grid Shift Transformation to point to the copied folder.
6. In Tools > Options, change the Bound Transformations environment setting to point to the copied boundcrs file.
7. Save the new settings.
The boundcrs file must be modified to associate the grid shift to a specific transformation
For example, the coordinate reference system AGD66 can be configured to the EPSG:15786 grid shift transformation through the boundcrs.dat file.
1. Copy the Gridshift folder to a new location.
2. Copy the boundcrs.dat file to the new location.
3. Copy the Australian grid shift file A66 National (13:09.01).gsb to the new location.
4. Add the following entry to boundcrs.dat in the copied folder: AS66, EPSG:4202, EPSG:15786 where
• AS66 is a map definition file entry.
• EPSG:4202 is the EPSG equivalent to AS66.
• EPSG:15786 is the EPSG code for the Australian grid shift datum transformation.
5. In the Options dialog box, point the Bound Transformations setting to the copied boundcrs.dat file.
6. In the Options dialog box, point the Grid Transformations environment setting o the copied Gridshift folder.
After the modified environment settings are saved and Options dialog box is closed, close the HPD editor and reopen it again.
When data from Australia is displayed in the HPD editor, that projection can be selected using the View > Change Coordinate Reference System command.