Real-World Shadows, how to?

Hi everyone, and thanks in advance for your help!

I’m totally new here and to Sketch Up, so I’m sorry if this question has already been asked and solved, but I can’t find a proper reply.

My point is, I’d need a step-by-step help in casting real-world shadows on my model.
I’ve got the basic idea and procedures, but my shadows don’t come out aligned with the real ones, and I’d like to understand why. (They are always 60 or 70 cm off).

I’ve built a small terrace model, with real measurements and TRIED to geo-locating it, which is where my first issue lies.

I mean, please, try to bear with me.

I’ve got my GPS coordinates using a smartphone placed on the terrace ground, and put them into Sketch Up.
Now, I wonder, when I do this, WHICH part of the model get those coordinates? There’s a way I should tell Sketch Up which part of my model refers to that specific coordinates?

Which version of SketchUp are you using? Your profile is confusing and the version matters in this case.

How did you insert the GPS coordinates? What coordinate system are you using? Is your model oriented correctly in the model space? Maybe you could share your SketchUp model file with us so we can see what you have going on?

Let’s see, thanks!

I’m using the Sketch Up Free version (the web one) I log in on the site?

I’m inserted the coordinates with Hamburger Menu > Add location and written the coordinates in the box.

And yes, I’ll look at how to share the project.

Here, saved in the 2020 skp format.

Another Ombra.skp (448.8 KB)

Where would you expect the shadows to be for 4:33 PM on June 29?

This is what I see when I open your model in SU2020.

You’ve moved the axes a little although that has no bearing on the shadow display. I reset them. The guideline shows where the green axis line was when I opened your file.

The shadows seem reasonable for the location in Italy.

Here’s noon on 21 June.

Your room is floating 7 M up and out over the courtyard but maybe that’s OK?

The model is floating 7 m up 'cause in reality that terrace is a second floor terrace (like, ground > first floor > second floor) so it should be around 7 m high.

And yes, I had moved the axis a bit thinking that it could have some relevance, but it doesn’t seem to have… or it’s just me?

And, here:52ba4189964d631680a83af5733b4948f0572aa2_2_690x436

The red square shows how in reality the terrace is. I believe the fact that there’s a gap between the model position and how it actually is in reality is relevant…?

The model axes don’t have any bearing on where north is or on how shadows are displayed. The default orientation of the axes is such that solid green points north.

The model is indeed displaced from where you show it should be. It’s not far enough off that it should really be a problem as far as the shadows are concerned. Looking at the plan view with the camera set to Parallel Projection helps you get a better idea of it’s lateral displacement.

I’m not sure if I say a right thing here: moving it some meters left or right, actually change something in how the shadows are calculated or not?

Or it’s just that I CAN’T expect an accurate enough simulation, and that sixty or more cm gap from reality is something will always be there?

Moving the model a few meters won’t really change the way the shadows are displayed. It wouldn’t make a noticeable change in the angle of your shadow if you walked a few blocks down the street, either.

I don’t know what the precision of the shadow calculation is for the free version of SketchUp but I would expect it to be plenty close enough for hobbyist use.

The sun is so far away that the gross location and time of day by far dominate the calculation of shadows. Move a few meters laterally and the shadows move the same amount. Move vertically and it is as if you are scaling two sides of a triangle (the height and the length on the ground) by the same amount.

However, it is quite possible that a difference in the coordinate systems used by SketchUp vs your GPS or in the day of year and time of day could cause what you are seeing.

That might be but evidently it’s reasonably close since my addition of the location snap shot seems to be about right, too.

I’m no expert, but I was wondering about the coordinates SketchUp uses to calculate the sun position vs location on the earth to generate shadows. Since the earth isn’t an ideal surface, there is room for error. In an experimental KML importer I wrote, I saw some substantial errors between locations in Google Earth and the geolocated SketchUp model using the current map sources, mainly in elevation.

There is a Solar North extension. Presumably that’s needed for some reason.

But of course that won’t do the OP any good since he is using SketchUp Free.

Mmm, firstly, thanks to everyone that’s supporting me here!

Then, tomorrow I’ll try to provide you a screen of my model shadow position VS real shadow position, so we could try to understand if it’s a minor issue or what.

Good point. I was mainly pointing out that if there is an extension for that, it suggests SketchUp has imperfections when it comes to knowing where the sun is.

The Solar North plugin was written long ago to allow users to change where north appeared to be so they don’t have to rotate the model in non-geolocated models. This allows the use of the standard views while also showing the sun coming from the correct dimension. You can then use the Front view for the front of the house even if the front of the house faces north. If I remember correctly this plugin pre-dates the first geo-location feature that used Google Earth.

Here, this is a comparison, taken at 12:50 PM. As you can see, there’s a visible difference, with the real world shadow behind the Sketch Up one.

And, later in the afternoon, the difference appears more evident, uhm.

did you correct for the summer time? (UTC-01:00)

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Uhm, I’m not sure what you’re talking about, Mike?

(Actually, I don’t have the slightest idea).