Sun angle off?
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Just the other day this was discussed. I believe it has to do with GoogleEarth's method of projection, or someone mentioned local magnetic vs. true north variances. Dig around through Active Topics back several pages, possibly a week ago. This could provide some insight. Of course, someone may reply who can quote chapter and verse for you.
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Was it Magnetic North and Solar North? I think TIG said it was 3 degrees difference. But don't quote me on that.
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The difference actually depends on where you are exactly. This is not necessarily the magnetic vs. geographical difference (sun angle should not depend on this but solely on geographical position which is based on geographical north).
I have also noticed some weirdness when I was trying to get this light of the rose window to be exactly in the sanctuary. SU and Twilight (Kerkythea) has some completely different sun angles. I do not know which is "right" however. The model is geolocated.
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GE 'north' and real 'solar north' are not always the same... but what's the problem?
The magnetic north pole is in Canada and not the Arctic that Long/Lat lines on a model globe might suggest - they are just different things... -
I take that back. Re-figured everything, Sketchup is very close. NOAA's solar calculator gives the solar elevation here on Mar 21 at solar noon as 41.73 degrees. Sketchup, as near as I can measure, gives 42.003 degrees. I'm happy with that.
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@bob777 said:
I take that back. Re-figured everything, Sketchup is very close. NOAA's solar calculator gives the solar elevation here on Mar 21 at solar noon as 41.73 degrees. Sketchup, as near as I can measure, gives 42.003 degrees. I'm happy with that.
How did you take the 'altitude' into account ? -
@mitcorb said:
..... I believe it has to do with GoogleEarth's method of projection, or someone mentioned local magnetic vs. true north variances....
Sun shadows have nothing to do with magnetic north. That spot (as TIG mentioned) is in northern Canada and isn't a fixed location. Actually it is said to be moving in the direction of Russia with the about 60km/year and speed still increases.
(Due to inner earths material flows)
"Only" your compass bearing will change.
Geo north is a fixed spot way up north. Where all longitudes "meet". Cold! -
Gaieus has posted an excellent visual response for the error in SketchUp: http://www.google.com/support/forum/p/sketchup/thread?tid=65a6f337a77e8197&hl=en
You will note that solar positioning for noon should be due South, not 8-10 minutes into the afternoon, and that the apparent declination of the sun is lower than it should be for the day and locale. These are potential errors in the equation of time and translational errors that may be due to assuming the surface of the SketchUp model is at the center of the Earth. By viewing the full forum discussion linked above, you can observe that the SketchUp developers do not appear to know of the original scientific literature that initiated this model. This is a matter of professional documentation that has not been updated with the expanded user base, and this is an ethical problem found when coding poplar software based on science.
A SketchUp employee's responses to my concerns from case #565706984 (Jan 4 and 13, 2010):
@unknownuser said:
"We've done some investigation over the weekend, but we don't actually have any more information to provide. We don't have a particular reference document, paper, or source for our algorithms, so there isn't a location to which we could point you for reference. Furthermore, the solar calculations were implemented early on in SketchUp's development, and the people who initially worked on them are no longer with the company."
AND
@unknownuser said:"As we mentioned before, the solar calculations in SketchUp were written a long time ago without a specific reference to the academic source."
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That's actually what I'd already posted here (above) and just reposted on the Help Forums.
Let's hope John (that "Google Employee") will also chime in here (as he is a member and has been quite active today - BTW John, it's Saturday, don't you have better things to do over the week-end?
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Hey Gaieus,
Did you ever figure our the difference between your SU model and twilight(kerkythea) models? Was it just a matter of geolocation and magnetic declination?
I made a simple sundial model in SU and verified Google's equation of time to be accurate relative to the accepted equation from Duffie and Beckman.EoT = 9.87sin(2B)-7.53cos(B)-1.5sin(B) , where B =(day#-81)*(360/365).
Based on this, the sun should be in the right point in the sky at all times in SU.
nick
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No, I have not (more exactly that whole project is now put a bit aside)
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So I am having a problem that seems to not be related to magnetic declination but decided to post in this thread since it seems like there are many here that have looked at this particular tool.I have pro 2013 and have successfully loaded the toolbar and it seems to work though I have not tried all of the functionality yet. I do not want to change the default settings untill I understand something, hopefully developers are watching this thread.
I have imported a scene from google maps and with it the geolocation of the project (prior to installing the north angle toolbar). On google maps north is always straight up. When I use the north arrow to display the north angle it is around 27 deg off. This could not be the magnetic declination difference since it is only 8.8deg for this area. How does the default north arrow calculate the default position if not from the geolocation? I have moved the default axis many times while modeling, could this have caused the confusion? Is there a way to get the north arrow to snap back to the geolocation?
see attached
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