Why do I get warnings on datums when connecting to 3rd party data sources? And how can I fix them?
The main cause of this issue is that the connection to the 3rd party data source will always look to assign a known CRS/Datum for the connection. This stems from Petrosys’ ability to convert coordinates “on the fly”, from the connection CRS to the mapsheet CRS, in order to display the items in the correct location.
Sometimes this can lead to a problem when the well-known text string for the CRS of the 3rd party connection does not match any known ones we have in our datummap.dat file.
Which can lead to errors like the following:
The error indicates that, in this case, the connection to OpenWorks (ow_datum) could not find the datum string called “World Geodetic System 1972_1” in our datummap.dat file. Often, this can simply be that the datum, as stored in OpenWorks, happens to be called something slightly different to what we expect, but the parameters are in fact the same.
To fix this issue, check what OpenWorks believes this datum to be (check the parameters for this datum as stored in OpenWorks) and then compare it to one of our known datums. Edit the datummap.dat file and place a single line in it that maps this OW datum to one we already know about. Simple!
In order to check the parameters in our system, simply go to Mapping > Admin > CRS > Geographic CRS Editor and search the list for something similar – most likely WGS72 – and then click on the datum editor box. For example:
You can then check the parameters that go to make up this datum (spheroid, prime meridian) and if they are the same as those in OpenWorks then the name is likely slightly different. In this case one can assume that the name in OpenWorks as listed is World Geodetic System 1972_1, where we do not have one with the “_1” listing).
So you can now take a copy of the datummap.dat file (if it has been previously edited a copy should already be in the $ps_local folder, but if not then the standard one can be found in $ps_misc) and then place this in $ps_local. Edit the datum name in the error code to map the OpenWorks datum to the Petrosys datum.
For example, you would copy the original line in the file like this:
WGS72,6322,World Geodetic System 1972,WGS 72,103,World Geodetic System 1972,””,
and paste it at the top of the file and edit it to reflect the name as in the error message, like this:
WGS72,6322,World Geodetic System 1972,WGS 72,103,World Geodetic System 1972_1,“”,
(in this case the ow_datum happens to be the 6th column in).
Once saved into $ps_local, the next time you connect to this OpenWorks project in order to display data the error should be gone.