[SIS-145] Datum aliases for various producers

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: Referencing
• Assignee: Unassigned
• Reporter: Martin Desruisseaux
• Created: 26/Nov/13 04:11
• Updated: 21/May/18 15:06

Description

When comparing two geodetic datum for equality, the datum name needs to be also compared because it is the only way to differentiate two otherwise identical datum - comparing the ellipsoid axes is not sufficient. However, different producers format the datum in various ways:

• EPSG uses human-readable texts (e.g. "St. Paul Island").
• Many other producers replace spaces and punctuation by underscores (e.g. "St_Paul_Island").
• ESRI adds a "D_" prefix in front of datum names (e.g. "D_St_Paul_Island".
• In some rare occasions, some producers may use completely different names.

We need to be able to detect when two datum are the same despite some variations in their names. In GeoTools, datum aliases were specified in a CSV file named DatumAliasesTable.csv. We can not port this file to Apache SIS for licensing reasons, and most of this port is not needed anyway. Applying the following rules during name comparisons is sufficient for the majority of cases:

• Ignore upper/lower case.
• Ignore any character which is not a letter or a digit.
• Ignore the "D_" prefix

However we still have the cases of completely different names or abbreviations. In many cases, the alternative name of abbreviation is in the EPSG database (e.g. "Nouvelle Triangulation Francaise" and "NTF"). But there is some remaining cases where the alternative name is not in the EPSG database neither. For example "Bogota 1975" is named "Bogota Observatory" by Oracle.

We may need to identify which datum fail to be considered equivalent despite the above rules and EPSG aliases, and declare our own aliases for them.

Issue Links

• is depended upon by: SIS-117 Allow definition of custom CRS by properties files