Reprojecting DWG file

[Sitaneph]

I have a DWG files which has its own co-ordinate system, which i need to get into MGA Zone 56. I know that the 0,0 on the DWG is equivalent to 314500, 7366000 in MGA.

 

I have not been able to reproject this using the register vector utility as it does not seem to be working properly. When i select the map for the registration points it doesn't bring it up.

 

I have also tried to offset the a layer the required distance then save in the required projection which results in the drawing getting rotated 90degrees and getting skewed.

 

Does any one have any suggestions how this can be done?

 

Steph

[Kannan Krish]

rubber sheet in autocad can do it, doesn't it.

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[Sitaneph]

However i don't have access or ability to use Autocad. I just have the file i have been given. I find it very frustrating that this is such a difficult task considering all i need to do is 'shift' the data.

[Robert Crossley]

Hi,

 

You could import the data in as a non-earth coordinate system, then export as Mid/Mif.

 

Then you can redefine the projection in the header of the mif file, and put an offset in.

 

Or you could be as blunt as importing the drawing to the right projection, inserting in a point of known coordinate, then select all, and drag all the objects to the right place on earth.  This will only work if the units are the same and north is the same in the autocad as for MGA.

 

The issue with any of these is if the projection system has a different north.  The way I understand it is that “north” in a zonal coordinate system is parallel to north at the central meridian, and thus will not be pointing to the true north anywhere else in the zone.  Whereas in lat/ long projections, north will always be towards the coordinate x, 90.

 

Of course autocad operators have been known to orient themselves so that the site fits nicely onto a page rather than where it fits on earth.  In which case, you’ve got a major problem.

 

R

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[phamkhai tan]

You could use FME to translate, rotate and move your data.

2013/3/18 Robert Crossley <rob...@wotzhere.com>

[Mats Elfström]

Hi!
Phamkhai is right.
I once got a very complex dwg drawing, where many people had spent countless hours assembling historical information for an old chemical plant site, almost a 100 years of knowledge. One purpose was for soil remediation.
The problem was that at some point, someone har rendered the information useless by rotating the drawing and put it into paper coordinates.

Only with FME, I was able to salvage the entire data set by rubber sheeting it to identifiable control points on current map data. That was no matter of a simple shift and rotation, because the underlying map was in an obsolete projection for the area. The workspace I created also fanned out the information by cad layer and wrote it all to an ESRI file database for the continued work.

Professional work needs pro tools.

Regards, Mats.E

2013/3/20 phamkhai tan <phamk...@gmail.com>

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[college.atlas]

Agreed FME is the Rolls Royce when it comes to this type of task with a very similar price tag.

MI is hopeless in this respect Steph. (20 year veteran)

As you've identified CAD is a plane grid. Unless you know there are distortions like rotations and scales then yes, a simple shift is all that's required.

I'd suggest downloading an open source or freeware CAD package that supports DWG. Shifting the file and then just performing the import. 

I'd also be more than happy to perform this task for you.

If you want to put the file in a dropbox and send me a message to let me know where it is I'll convert and send back. college.atlas(at)gmail.com

As a tip in this area, AutoDesk have a free tool called TrueView. It's a DWG file viewer. This also has a conversion tool to convert any DWG version file all the way back to R14 DWG. So any tool you can find that deals with CAD can be used even if it only supports earlier versions of CAD. There may be some loss of detail but you'll get most of it.