Frequently asked question
Why does the Robinson projection from ArcInfo Workstation not correspond with the Robinson projection in ArcGIS or the one in ArcView?
Answer
** Internal Publish Only! This article may contain information that is not intended for external circulation. **
When map projection support was added to ArcInfo workstation the main part of it was adapted from a USGS program called GCTP. Later, a contractor added support for more projections that we call EGCTP. Beyond these two main pieces, ESRI reworked parts of both code besides adding support for other projections and datum transformations. The Robinson projection is part of the EGCTP code.
Later, the ArcView team implemented a separate set of code for map projections and datums. While some QA was done to make sure both systems were compatible, not everything was checked. The Robinson projection in ArcView does not agree with the one in workstation.
Some time after that, around 1996, a new set of code to implement map projections and datums was written from the ground up. The way that coordinate systems were defined was changed, making them more flexible, easier to update, and re-usable. Support was also added for some new things that were essentially impossible in workstation or ArcView. An accurate history and references for the code was also created, which doesn't exist for the workstation code.
These changes turned into the Projection Engine. ArcSDE was the first product to use it, with version 3.0. MapObjects incorporated it with version 2.0 using Projection Engine version 3.0.2. ArcGIS added it for 8.0.1. The ArcView Projection Utility used the MapObjects version at 8.0.1, so is several revisions behind. ArcGIS and ArcSDE always use the current version of Projection Engine. MapObjects uses the most recent version whenever they do an update.
The version of Robinson in Projection Engine matches the one in ArcView. It also matches the documentation that ESRI has on the projection. The one in workstation is not necessarily wrong, it is hard-coding some value or scaling the data in some way that isn't done in other products.
Probably at some time in the future, a 'Robinson_AI' projection will be added to the Projection Engine so that coverages in the workstation Robinson projection can be used correctly.
Article ID:000004956
Software:
- ArcMap 8 x
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