nanomechGoogle SketchUp: Where is the Sun?
Posted by nanomech on 2010/01/24
As a researcher and educator in solar conversion systems design, I am sharing my concern about Google SketchUp for professional use and energy analysis. Through a multi-week correspondence with an unnamed member of the Google SketchUp team, I have learned that the team is unaware of the accuracy of the algorithms underlying their ShadowInfo and ShadowInfoObserver classes, and do not have the resources to collaborate to attribute source documents to the error in their models. Simply put, they do not know if the sun is where it should be for a given location/time on Earth. These core algorithms relate the solar Equation of Time (describing the difference between apparent solar time and mean solar time) to latitude position, solar declination, solar azimuth, and hour angle. If you and your colleagues find this of interest, I would ask you to contact the SketchUp team directly (sketchup-help@google.com) with common concern, as I have not had success in encouraging SketchUp to make this important information transparent to the user base. Arguably, it would not be a challenging problem to solve, if the user base could simply see the “snippets” of geometry algorithms. However, I am concerned that there may be legal consequences to those who use SketchUp for professional applications (such as your own firm), should SketchUp be found to be in significant error when used to prove or disprove data.
From the Google SketchUp Team:
“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.”
Thank you for considering this unusual failing in an otherwise highly useful software piece.
Dr. Jeffrey R. S. Brownson
Dept. of Energy & Mineral Engineering
The Pennsylvania State University
nanomech@psu.edu
redsteel25 said
So, any news on this one? and one important question, do you have any idea about how to calculate the right sun position and by default the shadow cast? I mean, is the error that big? or it’s just a matter of compensating some hours. Let’s say for argument’s sake that I want a shadow at 4:30pm, can I fix the error using the sun at 5:30pm?
nanomech said
No response from Google SketchUp–however I have received responses from my peers who agree that there is an ethical problem occurring here. Perhaps it is time to ask again–maybe I will even get a “name” when I correspond.