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We've been given a DWG file from a topographic survey of our garden. It looks great but when I try to measure dimensions of objects in Autodesk I know the real world size of, they're off by a factor of about 6 which means I cannot actually use it.

Here in the UK I would expect everything to be in metres but how can I check, because something seems screwy?

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  • $\begingroup$ Did the person who made the DWG file measure the garden accurately, or is it just based on guesswork? You don't really need accurate measurements for designing a planting scheme (plants don't care if they are not exactly one meter apart or whatever), but if you are doing any building construction work you might need them, of course. $\endgroup$
    – alephzero
    Commented Feb 23, 2019 at 13:03
  • $\begingroup$ All you need to check the measurements is a meter stick, which you can make from anything available. $\endgroup$
    – alephzero
    Commented Feb 23, 2019 at 13:06
  • $\begingroup$ @alephzero It was a professional surveyor creating it for a planning proposal - every tree measured, etc. Everything looks super-accurate but when I create a 1x1m rectangle or place a dimension of 1m in a new layer (just type 1.0 enter) it is about 20% the size it should be. Without being an expert on paper/model space, the plan itself should have units/scale built in right? I can't tell if it's user error (90%) or some systematic error in the file $\endgroup$
    – Mr. Boy
    Commented Feb 26, 2019 at 11:01
  • $\begingroup$ What settings did you have set in your software? Is it possible there’s a meters/feet/millimetres/inches conversion error? $\endgroup$
    – Jonathan R Swift
    Commented Oct 22, 2019 at 6:17

3 Answers 3

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  • Measure the physical distance between two known points in the garden - the further apart, the better. Let's call this 'M'.
  • Measure the same distance on the scaled drawing. Let's call this 'S'.
  • Scale the drawing by $ \frac M S $ and you should now have a 1:1 drawing.
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If it is a professional surveyor, when he/she create the DWG, on Units, he should work "without units", so later you can choose your own units.

Anyhow, you can choose your own units on a DWG file, because the relevant issue is that proportion are ok, so once that you change the units, everything will fit if the survey was properly down.

If you are not happy with it, you can just check one dimension (better as big as you can) and scale the DWG.

Depends on the software you are using.

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It was probably drawn in “model space” and then converted to “paper space” to fit the drawing sheet size.

Ask the draftsman to print to a specific scale. (It May take a few sheets, but you can fit together.)

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