Inaccurate shadow casting in Sketchup free

shadows

#1

Hi guys, I’m working on a model in Sketchup free. My goal is to get some accurate shadow simulation for planning an array of solar panels.

A few years ago I used the standalone version and had quite some settings for the shadows, but all I’m seeing now are the time and date. So far so good. I’ve added my location and rotated my model to match the map, next I wanted to check if my shadows are pointing the right direction at the time the sun is exactly in the south. For my location this would be at around 12:40 GMT+1, however I don’ t have a clue which timezone sketchup is using.

It can’t be using the same timezone as the location on the map as it goes completely dark in sketchup at time: 17:30 & date 09/25 while in fact the sun was still shining outside.

Does anyone have an idea how Sketchup Free handles time zones?


#2

As it is, SU Free web app does not provide the user a way to define UTC Offset.
Moreover, I find no way to confirm which way is true north.
NB: Add Location in the desktop versions of SU typically swings true north away from the green +Y axis.


Use SU Pro and the Solar North plugin.
https://extensions.sketchup.com/en/content/solar-north


#3

Hi Geo, thanks for you reply. Does this mean that SU Free uses UTC as standard time zone? I’ve been playing around with the shadows and it looks like with UTC+1 the sun is coming from the south. For my loaction I was looking for the sun to be in the south at GMT+2 12:40pm, in Sketchup I need to set the time to 11:40am for the shadows to be correct. Looks like it is not taking daylight saving into consideration.

When adding the location it looks like the orientation and rotation of the map is geografically correct. I’ve rotated the axes so I still could model using the axes.

Unfortunatly I can’t justify spending almost $700,- on a pro licence just to simulate some shadows for my solar array.


#4

Nor does SU Pro take DST into consideration.
Initially, the Add Location feature ‘guesses’ the UTC Offset using the theoretical 15° of Longitude = 1 hour
That initial ‘estimate’ can be off by hours depending upon location and time of year.

DST along with the convoluted nature of real-world local time conventions obligates the user to confirm the correct UTC Offset in the Shadows dialog. Again, SU Free web app does not provide the user a way to define UTC Offset.


I take it you have already used the SU Pro 30-day free trial.

There are four parameters that must be set correctly to achieve accurate sun and shadows.
Geographic Orientation — Relationship of True North to the model.
UTC Offset — The difference between local time and the C oordinated U niversal T ime standard.

Geographic Location — Latitude and Longitude
Time — Year, Month, Day, Hour and Minute

SU Free web app lacks two of them, as well as the ability to manually* geo-locate the model.
*Manual geo-location retains the default alignment of true north with the +y axis.


#5

Wow thats an eye opener for me. Thanks for pointing that out for me. I wasn’t aware af all those limitations in the free version. It would be great if this information was part of the help file in sketchup free, or at least… I could not find it in there, although it may be due to my lack of searching skills.

I’ve used a a trial for sketchup make in Juli this year, so I should be able to use a trial version of Pro now. I’ll give that a go. Thanks for the tip.