Aligning the Sun in SketchUp

Adjusting Earth location to create the right shadow alignments

I admit it, I obsess about sun angles.  It is my inner mathematician colliding with my inner architect.  I love how traditional architectural elevations rendered in the Beau Arts style provided shadows showing the depth and relief of the facade. This image style still works even for modern, low relief buildings as shown in this rendering of Portland’s ,  12W building by ZGF.

Direct rendering engines, such as the one built into SketchUp, are great for generating the clean crisp shadows required for these images.  But it is difficult find the right dates and times to position the sun at precisely the angles needed to cast the desired shadows.  SketchUp does not provide for manipulation of the sun position directly (as can be done in Rhino, kudos to them!). And while you can use date and time sliders to move things around until you get something that looks good, it is difficult to get just right?  And once adjusted for one elevation, how do you expose successive faces of the building for the others?

Shadows cast across the face of Portland's 12W building.

I found a solution by using an object called a “shadow box” from an old, used, hand-drafting book by C. Leslie Martin. Martin used this simple cube-shaped ”box” to illustrate where shadows should be drawn, in SketchUp it can be used to dial in exactly the location, date and time required to cast perfect shadows.

First, I got close by ignoring the geolocation and manually my latitude to 45 and longitude to 0 degrees in the “Set Manual Location” window under “Model Info->Geo-location.   I then adjusted for solar noon on the equinox in order to align my shadows precisely along the north vector, which defaults to the Y-axis.  The magic date and time settings are 9/21/2011 at 11:53AM and set by tweaking the values in the Shadows window.  Not perfect but as close as can be gotten with minutes being the minimum time adjustment value.

Initial construction of shadow box showing crosshairs and north angle 0. The orange line along the Y-axis marks north.

Next I rotated north 45 degrees using the Solar North toolbar in SketchUp 8 Pro. Why rotate north angle instead of rotating the model?  SketchUp provides preset orthogonal views aligned to the default axis.  Assuming your model building has faces constructed orthogonally to those axes as well (a good idea for stable modeling) it is easy to expose each successive face of the building by switching to its view and setting north to the respective 45, 135, 225, and 315 degrees.  Rotating your model is hazardous as it can introduce tiny errors in point coordinates that will cause much grief later on.

Final shadow box settings with the crosshairs aligned to the box base corner.

The sun is now 45 degrees off the building face, but we also need to adjust its elevation to get a vertical angle 45 degrees.  Don’t touch that time and date!   Instead, adjust your longitude under the “Model Info” dialog so that the shadow box “crosshairs” directly align with the lower back corner of the box.  The magic latitude was 55.4 degrees N.  Now by changing the north angle to each respective quarter and you can quickly export beautifully stylized and consistent elevation studies.  Separately exported images for lines, materials and shadows can then be recombined in Adobe Photoshop to further enhance the renderings.

Download your very own SketchUp shadow box here!