Autodesk Revit DWF Measurement Correction

In an earlier blog posting, I covered the steps for publishing DWF files from Autodesk Revit. A typical architectural workflow while creating construction documents is to print out a sheet, have it reviewed and marked up by the project architect or other professional, and then return it to the originator of the sheet to have the requested changes made. Autodesk Revit Building enables an electronic version of this process by allowing you to export sheet views as DWF files. The DWF files can then be marked up in Autodesk® Design Review (new name for Autodesk DWF Composer), and the markups can be linked back into Autodesk Revit Building to see the desired changes. Because they are linked, the Autodesk Revit Building file and the DWF file remain synchronized with regard to the markups.

In addition to marking up requested changes, project architects or other professionals can take measurements using Autodesk Design Review. A previous blog posting documented the measurement capabilities of Autodesk Design Review.

In working with our beta program, we discovered a slight anomaly that can occur with some 2D DWF files generated from Autodesk Revit. A linear measurement of 18000 millimeters was being reported as 18075.362 millimeters.

If you have never looked at an ASCII version of a 2D DWF file, it looks something like this:

---

(W2D V06.01)
(NamedView 0,0 1073231279,829315080 'Floor Plan: Level 1')
(Units Millimeters
                        ((3841200 0 0 0)
                        (0 3841200 0 0)
                        (0 0 1 0)
                        (0 0 0 1)))
(Color 0,0,0,255)
(LineWeight 834601)
(LineStyle
(DashStartCap round)
(DashEndCap round)
(LineStartCap round)
(LineEndCap round))
(Viewport 'Floor Plan: Level 1'
   (Contour 1 4 0,829315080 0,0 1073231279,0 1073231279,829315080)
     (Units Millimeters
                        ((23746.352529 0 0 0)
                        (0 23746.352529 0 0)
                        (0 0 1 0)
                        (0 0 0 1))))
(Font (Pitch default) (Family unknown) (Height 8116322))
(Font (Height 9739587))
f
(Node 24 'Linear Dimension Style [125062]')
(LineWeight 325221)
   P 3 321984240,577464630 294086597,577464630 286932870,577464630
(LineWeight 325221)
   P 3 321984240,148241024 294086597,148241024 286932870,148241024
F
(Color 0,0,0,255)
(Font (Rotation 16409))
   (Text 287821116,349613220 18000)
(EndOfDWF)

---

Lead Software Engineer, Eric Haines, analyzed this DWF and observed.

1. The Units opcode sets the scale. This identifies how many logical units per millimeter. The scale factor here is 23746.352529.

2. The two leader lines for the measurement labeled 18000, on the far left, are:
   P 3 321984240,577464630 294086597,577464630 286932870,577464630
   P 3 321984240,148241024 294086597,148241024 286932870,148241024

3. The distance between the lines in Y is:
   577464630 - 148241024 = 429223606.

4. So, the length between these two should be:
   429223606 / 23746.352529 = 18075.348855

The Autodesk Design Review computations are correct. The program shows 18075.362 - only a slight difference from the calculations above. Eric concluded that the DWF has the wrong scale for its data in the Units opcode. For Autodesk Design Review to compute 18000 the distance, given the logical units in the drawing, the scale that should be used is:

429223606 / 23845.755889 = 18000

So the current scale being stored in the DWF file by Autodesk Revit does not match what is needed. The scale is considerably different, 23746.352529 vs. 23845.755889. The issue has been corrected and is available as an Autodesk Revit update.