Problem with UCS vs World

[neilyj666]

I'm working with an electrical contractor on a large substation project who tends to produce CAD files at some random coordinates, always orthogonal to E/N and always works in mm. I have been provided with a drawing that has a UCS that coincides with the real world coordinates BUT when I xref it comes in at the random world coordinates used originally.

I can't share the drawing unfortunately but can something cunning be done so that the UCS that is being used becomes the World coordinates that I require??  I'm not over familiar with UCS manipulation as I always work in World Coordinates as it so much simpler but I can probably fudge it if all else fails.

Thanks

Neil

[ChicagoLooper]

The x,y's in modelspace don't necessarily EQUAL real world coordinates. It may be consistent with the real world OR it may not be.

Real world coordinates requires you to establish  your coordinate system BEFORE you start drawing your linework. In the event where you cannot establish your coordinate system beforehand, then you'll need to verify whether the existing linework is referenced against a properly established CS to begin with. And determining that can be tricky for a number of reasons:

1. You'll need to determine IF the electrical contractor is using a 'known coordinate system' and by 'known' I mean whether it is listed in AutoCAD's CoordSys Library.  Since there will likely be several CS's which are applicable to your site, you'll need to use intuition, know-how and/or luck to figure it out which one it is.
2. You'll also need to establish a coordinate system in YOUR drawing. It's best if both your drawing and the contractor's drawing are using the same CS, but if they're different, you can still reference it accurately using Civil3D or Map3D because the program can TRANSFORM from one coordinate system to the other. For example, in the USA, users frequently transform from NAD83 Lat/Long geographic coordinates that uses decimal degrees (not feet!) to a drawing with a projected CS that uses State Plane Zone FEET. 

Performing 1 and 2 above will ensure both drawings are using Real World Coordinates. If you do just one, you'll have issues. Accurate xreffing requires that each drawing knows where the other drawing is relative to the equator and North Pole.  

Since you didn't mention the CS the electrical contractor is using AND the CS assigned to your drawing, your question cannot be answered without guessing. Sharing your dwg file would be the fastest and most accurate way to resolve your issue but since you say it's not possible to share, your question can't be answered.

Of course, there's also the possibility he didn't properly georeferenced his drawing in the first place--he simply eyeballed where to move his linework.

[neilyj666 · Accepted solution]

@ChicagoLooper thanks for the reply - I suspect the drawing was originally started at or around 0,0 and F8 ortho was turned on to get lines nicely at right angles etc. The UCS in the drawing has been set such that the coordinates in the UCS correlate to my world CS i.e. OSGB1936.NationalGrid.

I drew a polyline as a tie line between two extremities and LISTed the coordinates (which were in mm). In a new drawing I drew the polyline using the LISTed coords but changed to metres and then copied, pasted, scaled and rotated the supplied data to match the tie line and so that it fitted real world coordinates. I have an EGL survey with a coordinate grid corresponding to  OS1936.NationalGrid and ID'ing several grid locations gave the correct coordinates.

Just several extra steps I wasn't expecting to have to do when I asked for a georeferenced CAD file....!!!!!! 

[ChicagoLooper]

Glad it worked out.