So, I recently modeled my home in Cincinnati while researching solar panels, and used the geolocation and sun shadows features. I noticed today, though, that the real sun is way north of where SketchUp thinks it is. Model’s lat, long, and orientation are correct. It’s not a time zone thing, as the sun this morning (mid April) was farther north than Sketchup thinks it will be at any date or time of the year. It’s actually a good thing for my solar panels, but now I’m curious about SketchUp’s algorithms for locating the sun. Anyone else here checked their shadows for accuracy?
I think that SketchUp uses grid north, which is what a typical map will show you. That isn’t the same as magnetic north, and it isn’t the same as true north. Here’s an article that explains the three of them:
When you know what true north is for your location, you can use this extension to adjust where north is:
https://extensions.sketchup.com/extension/393f5153-ba5f-4f5f-849f-46b32cf64bd4/solar-north
Being a bear of very little brain, I don’t quite understand this. It seems to be a problem with how you geolocate your site. Obviously, no one wants to get into the different types of north and have to make corrections if they don’t have to. So what is the SU approved method for ensuring correct geolocation and therefore correct shadow rendering?
I just tried changing the position of north using the Solar North extension and it does do what you would expect.
I have a site that gives a declination adjustment of 0 degrees 39.6’ E. In decimals, that’s 0.66 degrees E so I guess that is the amount you would set Solar North off axis? Obviously, such a small angle makes virtually no difference. Might be different in Canada!
But then I reset to on axis and took a look at the shadow cast for the summer equinox at midday. I expected it to be on axis but it’s not. I wonder why?
I’ve been in some long discussions about this. The reason for the issue is mainly that noon is based on a longitude line, and typically you are east or west of that line. So, noon for you isn’t going to be when the Sun is highest in the sky, unless by chance you are on one of the longitude lines.
Here’s an online calculator that tells you which way solar north is, for a given location and date:
Even at the midline of the time zone solar noon and clock noon almost never coincide because the length of our year is not an integer number of days. The length of a solar day is exactly 24 hours only four times a year.
Solar noon can be up to 15-17 min ahead of or behind mean clock time at different times of year, I learned in a recent talk by the chairman of the British Sundial Society on the evolution of sundials and timekeeping. Add that to the effect of being in between longitude between time zone boundaries, and you could be over 3/4 hr off.
But that isn’t the problem the OP asks about, which is the discrepancy between the real world sun’s altitude and Sketchup’s calculation which tells him the sun never gets that high in the sky in Cincinnati, as I understand his question.
None of the responses, including mine, explain that, unless the latitude, not longitude, is wrong either in the model location, or the real location.
A Google search tells me that Cincinnati is Lat 39.14deg N. What is set in SU?
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