changing data projection and extent

[Daniel1979]

I am a new user of AutoCAD 2004 but an experience ArcGIS user. I have a DWG file that was created without a projection and probably using feet as the unit of measure. I know how to get the data saved into a DXF so that I can view the data in ArcGIS but the data is displayed in the wrong place. I know I can move the data in AutoCAD to a known UTM (X,Y) coordinate but I don't know how to scale the data proportionally in order to get it to fit to my GIS data. Any ideas?

[Seann]

So you are trying to get the feet down to decimal? If so I would just type SCALE pick a point and scale by 1/12. That is what I think you are asking.

[Alan Cullen]

In order to give you a good answer, we need to know what units you require (feet, feet & inches, metres etc), and what units the acad drawing is in (type UNITS and it will tell you). We also need to know if you have a reference distance that you know the length of.

e.g. if the reference distance is supposed to be 100m and it measures 328.084 units in autocad, then we know that you will have to scale the entire acad drawing by a factor of 0.3048 to get it to the units you want.

[Daniel1979]

Thanks for the quick reply. Sorry for not providing you all of the info. The DWG is in feet and the project in ArcMap I will be adding it into is in meters, Projection: NAD 83 UTM Zone 18N. The DWG has no projection that I am aware of. I assume that the data was created and then rotated in order to fit on a landscape page format. I have rotated the CAD data in AutoCAD to be oriented correctly (north). The distance between A and B in AutoCAD is 573.8099 ft and the distance in ArcMap is 175 m. The distance in ArcMap represents the real world distance.

[Seann]

lol tag I'm out. Isn't there a rule when going to metric to times/divde by 25.4? Think I will let Alan help finish this while I watch and learn. :)

[Alan Cullen]

Okay....the 573.8099 ft in acad is actually 573.8099 acad units....you need to rescale the entire drawing so that the distance between A and B measures 175 acad units (which you will think of as metres).

...... 175 / 573.8099 = 0.304979 ..... the scale factor to use is 0.304979 :)

Edit...

for Sean...... feet x 0.3048 = metres ......... metres / 0.3048 = feet (decimal)

The difference between 0.304979 (derived) and 0.3048 is due to errors with the acad drawing or with the measuring.....so I always find it safer to actually measure a known reference length and calc the scale factor.....

[Daniel1979]

Thanks Allen! That helped me out a lot.

Cheers,
Daniel

[ChrisCMU]

I have a similar situation. I have some cad parcel drawings that are projected in UTM, but the client drew them in the wrong UTM zone. How can I re-project them into the correct zone to match up with the ArcGIS data I am bringing in (rectified images)?

I could project the GIS data to the wrong zone, but that would be against the goal if having good data accuracy.

This could be a simple question, but all my Autocad experience is in drafting and not GIS work.

[Alan Cullen]

If you have a point in the drawing with known UTM coords, then MOVE the entire drawing (make sure all layers are unlocked first) to those coords.

If you want to check the rotation you will need two known points.