DWG Export Scale problem

[Jonathan L]

We are experiencing problems exporting drawings to scale from VW 11.5.1 to Autocad 2004. The drawings come through legible but when objects are measured onmodel space they come out 1000 times smaller. I have tried changing units and exporting to both scale options. Makes no difference. If we rescale in Autocad the accuracy of the drawing goes so that it no longer corresponds to the Ordnance Survey grid it has been set to - ie the drawing distorts its position. Any solutions?

[Guest]

Have them check the units setting in AutoCAD and ensure it's set to a correct value.

[islandmon]

The problem is that VW uses a variable PageSpacescale whereas Acad uses a fixed WorldSpaceScale.

Therefore, VW metric is 'off' by 1000x and VW imperial is off by a factor of 1200x.

One possible solution is to set your VW Layers to 1:1 prior to export>DWG.

[Jonathan L]

Thanks for the explanation. However all permutations of settings in VWorks have been tried. With no success.

[Jonathan L]

Changing the units (this is Autocad 2007) made no difference in Autocad. Its possible that the original survey drawing that has been imported into Autocad is the source of the problem. To explain - the Vworks drawing has been created from Autocad dwg drawings - it works fine until I try and export back to Autocad. Originally I had to set the units in my Vworks drawing to meters to get the drawing to import to scale.

[jan15]

It's possible that the original survey drawing that has been imported into Autocad is the source of the problem.

That's caused a lot of confusion over the years. In the US, architects use inches as the CAD unit, but surveyors use feet, so when we use the geometry in a surveyor's drawing we enlarge it all by 12x. It's the same problem when both parties are using AC.

[Jonathan L]

Yes. The problem with this is that when you're dealing with 1000 x in metric land the accuracy of the drawing goes and you can't do any accurate site co-ordinates from it (in Autocad that is in this case).

Edited August 16, 2007 by Jonathan L

[jan15]

Do you mean it's not really a CAD issue, but simply that the surveyor didn't provide enough precision in his data?

[MikeC]

I am not sure exactly what your problen is but as a long time autocad user I suspect you are seeing a problem where there is none. As Jan15 pointed out this is an autocad issue and occurs acad to acad as well as vw to acad. In a metric enviroment architects and most others use mm as a base unit, surveyors have to be different, they use meters.

Foe example if an architect creates a building 7004x7004, scales it by 0.001 and imports to a survey drawing it will probably report the dimensions as 7.00x7.00. This does not indicate a loss of accuracy but simply that the dimensions have been rounded off to two decimal places. If you want to see 7.004 use the 'units' command to restore the third decimal place.

Were it me I would take a slightly different approach

1. Create a new acad file using your usual template (I assume units would be set to show no decimal places, as would be the case if mm were intended to be the base unit)

2. xref in the floor plan

3. xref in the survey plan applying a scale factor of 1000

4. zoom to extents.

You can also do something similar in VW