Accuracy of Shadow Studies in Viz

[tkbyrne]

A client has questioned the accuracy of a shadow study, first time ever, how can I prove that the sunlight positioning system used in Viz 2005 correct, is the system they use a certified system and if so what is that system?

[Arnold Gallardo]

Well in the absence of a site photo reference. I would try to first verify the location via Google Earth and then try to see if the plans you got are accurate. Finally try to see if the program you used at least complies with CIE Skylight model. Maybe a Viz 2005 user can verify that. I only beta tested Viz 2006 so I don't know what was in 2005.

 

An image would help though for us to evaluate what your client is seeing It would help if your rendering shows both the direct sunlight illumination as well as the skydome contribution and where the confusion resides.

 

BTW there is no certification. What most 3d apps use is based on the CIE Skylight standard models. These have limitations though since the skydome and sunlight contributions are generalized. Having an ultra accurate skylight

rendering would require raytracing (or finite element radiosity and other approaches) the whole sky instead of sampling the dome and shooting luminance from it.

[Justin Hunt]

We questioned this a couple of years ago with other software. We asked the developers if they would confirm the accuracy of the daylight system and the basic answer was, "not in court".

 

Bare in mind that in the documentation it states that it is accurate. Unfortunatly that wouln't standup in court.

 

To test the accuracy we found 3 online shadow study tools (I cant remeamber which though), two of which were used and endorced by the US military and navey. All three gave slightly different results but significantly different from our software.

 

I would say that Viz is not the most accurate shadow analysis tool around, not in legal terms anyway. for example ,the placment of the North point isn't accurate enough.

 

To cover your rear I would ask a professional ESD designer or at least ask you local council which is their preferred analysis tool.

 

JHV

[Arnold Gallardo]

You can always try to replicate your results using Dialux:

 

http://www.dialux.com/

 

I forgot, you should also try a functional demo of ECOTECT:

 

http://squ1.com/ecotect

[tkbyrne]

Many thanks for the help.

I myself believe the accuracy is fine.

Unfortunately in our city we have a kind of activist who would prefer if our city stayed in the 50's, he objects to every new development that is proposed sending appeals about anything and everything. He has appealed this development because, in view of his degree in mathematics!, and after making his own calculations, the study is wrong.

We'll see what happens. Thanks again