Why does a CAD survey ALWAYS come in scaled??

[patricks]

It seems like every time I link in a CAD survey file, it comes in at 1/12 size. I checked the CAD file, the units are indeed set to decimal FEET, but if I link it in using Auto-detect units, it comes in as inches instead of feet. So 150.5 feet in the CAD file is read as 150.5 inches when linked in.

I can set the units to Feet when linking, but that throws off the Z elevation of the whole file, which causes all kinds of problems if I try to acquire coordinates from the CAD file, and create a topo surface.

I suppose I could scale the CAD file in AutoCAD, but why should I have to do that if it's already set to Feet units in the file??

*edit* I tried changing the units in the CAD file to Inches and selecting the option to scale objects in model space, but it left behind a few of the spot point markers. Most of them went with the rest of the model objects, but a few of them got left miles away.

[cporter.207875]

I always just resort to changing the primary units to inches in the CAD file to see if it is drawn to scale (it never is). Then I scale the drawing up to actual size before importing to Revit. I've never gotten a survey that imported correctly, and they have always been drawn at 1/12 actual size. Wish I understood the reasoning behind that.

[kathy71046]

I don't think Auto detect actually works...every time I've tried using it with a metric file set to millimetres it still imports as metres

[mthurnauer]

The reason is that many survey drawings don't have any units set

[patricks]

The reason is that many survey drawings don't have any units set

But the CAD drawing in question showed Feet when I brought up the Units dialog. That's why I don't understand why it doesn't come in as such.

[kingjosiah]

Patrick-

I think he was referring to the insert units variable as defined in the dwg. Type INSUNITS and see what it is set to (either unitless or hardcoded to something like feet or meters).

- Jon

[Joef]

An AutoCAD drawing is basically unitless. A unit of measurement can be whatever you want it to be. That is why you can easily use AutoCAD for astronomy or chemistry. If the units are set to decimal feet then whenever you type 1.5, you are telling AutoCAD that you want it to consider that to mean 1.5 feet. If you set up a drawing to be Architectural feet and inches, then when you type 1.5, you want AutoCAD to consider this to be 1.5 inches. If you set it to be Metric, then 1.5 will be 1.5 meters. It all depends on how you dimension your drawing.
That is why a drawing that is set up to use decimal feet will be 1/12th smaller than a drawing that is set up as Architectural feet and inches and why a drawing set up in meters will need to be scaled by 39.370077 to be the same scale as a drawing that is in feet and inches.

[cporter.207875]

An AutoCAD drawing is basically unitless. A unit of measurement can be whatever you want it to be. That is why you can easily use AutoCAD for astronomy or chemistry. If the units are set to decimal feet then whenever you type 1.5, you are telling AutoCAD that you want it to consider that to mean 1.5 feet. If you set up a drawing to be Architectural feet and inches, then when you type 1.5, you want AutoCAD to consider this to be 1.5 inches. If you set it to be Metric, then 1.5 will be 1.5 meters. It all depends on how you dimension your drawing.
That is why a drawing that is set up to use decimal feet will be 1/12th smaller than a drawing that is set up as Architectural feet and inches and why a drawing set up in meters will need to be scaled by 39.370077 to be the same scale as a drawing that is in feet and inches.

Very, very interesting...