Services that do not match the Web Map basemap coordinate system will be projected to align. If a transformation is required, a default transformation will be selected unless a datumTransformation is specified on the service from the time of publish.
This means that a user could have two 'GDA94' feature services. One published with no transformation (defaulting to 'GDA94 to WGS84 2') and another published with the old transformation ('GDA94 to WGS84'). The first will align data to WGS84@GDA2020 and the second will align to WGS84@GDA94, resulting in a 1.8m offset.
The end users can see that the services are both GDA94 but the only way they can identify the datumTransformation set from the time of publish is via the Admin REST API. Or externally supplied metadata.
It would be great if we can:
- Show the datumTransformation set for a service at the publicly accessible REST level or item details page
- Allow ArcGIS Online publishers to manually change the datumTransformation via the configuration user interface instead of having to invoke Admin REST API definition updates.
Coordinate systems and projections are intro-level GIS and we are relatively hamstrung to get data to align without the above. Sure we could improve publishing workflows, but what about external service providers? How do I know what transformation is set for a government ArcGIS Server service unless they have volunteered this information in the details or via their site?
https://doc.arcgis.com/en/arcgis-online/reference/faq.htm#anchor69
https://www.esri.com/arcgis-blog/products/data-management/data-management/taking-control-of-transfor...