discrepancy between the shadows of Revit and ArchiCAD!

[Anonymous]

I tried exporting my 3D model to Revit and tested the shadow study there, to my surprise there is a discrepancy between the shadows of Revit and ArchiCAD!

see the red line showing the extent of the shadow..

The settings seem identical, same city (same azimuth & altitude) same date (march 21 at 12pm) and they are both using the same model, 0.00 is at the same level.

Shouldn’t they be identical??

PS I dont think it is a daylight savings time issue, since the problem is not in the Azimut of the sun but in its altitude.

[Ignacio Azpiazu]

Hassanen wrote:
the problem is not in the Azimut of the sun but in its altitude

The azimuth is a bit different too, check out the right side of the funky shaped home near the center of the drawing.

I think I once read some Wiki article or something about the method ArchiCAD uses for its shadow studies.

[Anonymous]

I found the wiki article here http://www.archicadwiki.com/TechNotes/Sun_Study_Accuracy?highlight=%28shadow%29
but my discrepancy seems much bigger than that. (mine seems to be a 12m. discrepancy also in a 100m. tall tower)

[Karl Ottenstein]

Very interested to hear the resolution of this issue!

Have you tried the same model in SketchUp and Artlantis? I would hope we would not see 4 different solutions...

Thanks,
Karl

[Anonymous]

Perhaps I posted before testing enough, I just started from scratch with a simple test model and the shadows are identical between software. (see image)
So I’m still not sure what setting I had wrong that was causing this..

[Dwight]

That error would be the exact direction of North, were i betting.

[Anonymous]

As usual you are right Dwight! My project north is different; also daylight savings time was not set which I thought is automatic..

(Both settings I don’t know how to change in Revit, but rotating the whole model and using 11:00am instead of 12:00pm did the trick)
I guess the moral of all this is that we can be confident that the shadows done in ArchiCAD are accurate..

[Dwight]

Hassanen wrote:
we can be confident that the shadows done in ArchiCAD are accurate..

As accurate as in Revit, at any rate.