ArcSDE CAD Client #10
They say you get what you pay for. In the case of CAD Client the no-cost extension linking AutoCAD and Microstation to ArcSDE managed spatial databases; I think you are getting a good deal more. In the spirit of something-for-nothing here is a little bonus for CAD Client users.
Tucked away in one of the registry settings of ArcSDE CAD Client is a reference to an obscure function that was never exposed in CAD Client to perform coordinate projections and transformations. One of the reasons it was never exposed was likely its limited usefulness. However, it is there and you can use it … at your own risk.
The tool will project or transform CAD Elements from one geographic coordinate system to another. It will do it entity by entity. It will use the defining coordinates of an entity and simply move the coordinates from one projection to the other. Technically it is using the ArcSDE projection engine to move the defining points of an entity. That means for example, a circular curve entity is defined by its center point, start and end angles and radius, this is the information that will be used to modify that entites coordinates, not its endpoints. This means mathmatically at least, the data is not truely projected. In a true mathmatical projection circular curves might be projected into elliptical arcs.
The whole idea of projecting CAD data is a topic I may take up in another blog post some day. I would make the case that in most situations people want to transform their CAD data not project it.
The (esri_scTransform) is a function that you can run from the AutoCAD command line or Microstation Key-In. You can set the adjustment method to Transformation and/or Projection. When projecting you have to hit the configure button first to load various projections that can be selected from the pull down. This is used to limit the number of projections shown in the pull down picker. (kind of a weird interface…, but that’s how it works.)
If you have any questions about this tool don’t call ESRI they don’t know anything about it. This is an unsupported tool. Use at your own risk. (You might want to use the backup file capability on the options tab.)