Projection Issues between two CAD Files

[texian2112]

I just ran into a projection issue with a couple of AutoCAD files. There is a possibility that one of the files was originally in Microstation and in meters before it was converted to AutoCAD but I'm still trying to confirm this now.  The problem that I am running into is that AutoCAD Map doesnt allow you to xref or attach other CAD files and use  different projections. I have one file in Maryland State Plane, Feet and a second one which appears to be in Meters and I can't get them to overlay or for the file in meters to come in at the right location when it is xrefed. Any help would be appreicated. Thanks.

[AlmasSuljevic]

Hi texian2112,

Most likely this has something to do with units. Besides drawings being in different units, see insertion units and coordinate systems. Do you see any scales discrepancy or the draiwng just does not align correctly while scale is OK?

[AllenJessup]

Check the INSUNITS, INSUNITSDEFSOURCE and the INSUNITSDEFTARGET system variables in each drawing. If these are set correctly, you should be able to xref a drawing in Meters in to a drawing in International Feet and at least have the scaling right.

The System may be another matter. If the drawing you're trying to Xref doesn't have any Civil 3D objects in it. You can use a Map Query to convert the drawing to your current system.

Allen

[Sinc]

Keep in mind that XREF is a core AutoCAD command, which only understands how to convert between meters and International Feet, so you will get incorrect results if you're using US Survey Feet.

Also, the XREF command can't reproject data.  All it can do is scale the XREF based on the basic unit conversion factors, such as meters to International Feet.  For example, the XREF command cannot do things like take a UTM XREF and properly insert it into a State Plane drawing.

[Murph_Map]

As Sinc stated the Xref will not reproject however you can use the Map3D tools and use the map attach commands to bring in different dwgs with different projections provide you have the projections assisgned to the dwgs.

[Sinc]

But to add to Murph's comment, MAP projection commands cannot see any C3D objects, so all you can do is reproject raw AutoCAD objects.

[Murph_Map]

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@Sinc wrote:

But to add to Murph's comment, MAP projection commands cannot see any C3D objects, so all you can do is reproject raw AutoCAD objects.

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Right, but the OP thinks one of the dwgs came from MickeyStation so there should be no C3D objects in it.

[Sinc]

There can also be a number of annoying instances that happen when pulling in various flavors of MickyStation DGNs, though...  Some of the most annoying ones:

• TIN triangles come in as polylines, rather than 3D triangles, so an entire triangle is at a single elevation, and you get a bunch of "stepped" triangles, rather than a TIN.  Useless for creating a Surface in C3D.
• Random contours come in with a -1 Z factor instead of +1, which causes them to have a negative elevation.  Contours around these things have the proper +1 Z factor, so there are random contours that are at negative elevation when they should be positive (or vice-versa).  Never found any rhyme or reason to why this happens.
• Arcs often come in as Ellipses into AutoCAD, again for no apparent reason.  This can create a lot of annoyance in AutoCAD, since you can't combine these Ellipses into polylines, even though they have identical major and minor distances, and are really just plain arcs.  You also can't use them in many C3D commands.  The only option is to draw a new arc (or polyline) over the garbage ellipse you get from the MickyStation conversion.