The following discusses adding a new datum or ellipsoid. This functionality is only available in Bentley Map SELECTseries 3 or later. It is not found in MicroStation.
Locate, copy and rename the delivered ...\MapEnterprise\coordinate\seed\seed.dty file to a folder and name of your choice. If this file is to be shared among users, consider placing it in your Standards folder. For example: ...\WorkSpace\Standards\coordinates\CustomGCS.dty
In your project schema, or other configuration file such as your standards.cfg, create the variable MS_GEOCOORDINATE_USERLIBRARIES = Library[Name]. The Library is the name and location of your dty file. The Name is the name of the root node in the Select Geographic Coordinate System dialog.
For example: MS_GEOCOORDINATE_USERLIBRARIES = $(_USTN_SITE)/coordinates/CustomGCS[Custom GCS]
To verify that the variable is being read, start Bentley Map and open the Select Geographic Coordinate System dialog. Your newly defined node should be visible.
To add a new datum:
Right-click on the new folder and select Edit Datums > New and set the parameters for the datum.
To add a new ellipsoid:
Likewise, select Edit Ellipsoids > New to create a new ellipsoid.
To add a new geographic coordinate system:
Select an existing coordinate system from the delivered library, right click and select Copy.
Navigate to your custom folder, and paste.
Once pasted, you can edit the properties of the copy:
Edit the properties as needed. Note that custom datums will be available from the dropdown list:
If you want to add a Geographic Coordinate System, you only need to copy one from the list and paste it in your folder and so on.
Notice that the changes can't be backported. It means that this new seed.dty file won't be able to be read by Bentley Map SELECTSeries 2. Also, the file is self-content. It means that if you want to provide your Geographic Coordinate System information, inlcuding your personnal datum and\or ellipsoid, you will only need to provide the seed.dty. Everything is stored in it.
Finally, the file name can be different and can be store elsewhere. And in the variable value, you can add [string] at the end and get something like this : C:\temp\seed.dty[string] to see a different name of your folder in the Select Geographic Coordinate System dialog. Otherwise, the name displayed is the .dty file name.
For more details, please refer to the online help documentation > http://docs.bentley.com/en/Map/MicroStationMaphelp234.html