Sun setting - is archicad accurate?

[Arcadia]

I was checking the sun azimuth and altitude settings for a date and time after a client mentioned he was trying to achieve this in BIM explorer but it didn't seem right. After tacking down the figures for a date and time on the Geoscience AUstralia calculator I find it is giving me different figures to what archicad does. How is this possible?

For 21st September 9.00am Archicad gives

Azimuth 119.33
Altitude 31.19

The online calculator gives
Azimuth 60.39.20
Altitiude 30.59.06

I assume arcihicad uses true north not magnetic north?

[Arcadia]

And on a related note, when I export to BIM explorer the project north does not seem to be kept and the angles are all wrong.

[Steve Jepson]

What is the specific location?

I have done some sun/shadow studies for projects in Australia and one problem I ran into is getting the correct survey data. Magnetic north has shifted quite a lot since some surveys were made.
You may be stopped from getting a permit unless you can prove the shadows from your house will not put too much shade on the neighbors pool.
You will find quite a lot of difference even in official records that tell what direction magnetic north is from the same spot.

Also, magnetic north pole has been shifting towards Russia at 40 miles a year for the past decade or so.

You may need to calibrate north in ArchiCAD to match some actual compass readings and verifiable shadow lengths.

http://www.airport-data.com/world-airports/YMAY-ABX/



Even then you will probalby need to base the shadow lenghts on an agreed to set of data rather than actual observations. Good luck

[David Shorter]

Azimuth is the clockwise horizontal angle measured from true north. Unfortunately Archicad measures this from 3oclock in an anti clockwise direction hence the different figure. The position of the sun is essentially correct subject to the exact location being entered into the More Sun dialogue. The default city locations will need to be refined using government data (search for sun positions) this last is critical as 10 minutes at 9 in the morning can make a difference of 15metres to the length of the downhill shadow.
As far as the sun position in BIMx is concerned it does generally appear the about right but I guess GSHQ need to pronounce on this

[Steve Jepson]

I thought this was a very useful paper on the subject.

http://sites.google.com/site/khavrus/public-activities/SolarEng

ArborCAD ? http://www.chrisskellern.co.uk/software/download.htm

Shadowspro ? http://www.shadowspro.com/en/download.html