Rorschach Shadow Diagram

We’re developing a set of Grasshopper user objects to generate sun study diagrams using the DIVA sun vector component.  This post focuses on the overshadowing diagram, a powerful metric which offers comprehensive analysis for point of interest shading (more info). The diagram can be used for early site studies to consider shading based on existing context. It also demonstrates the impact of vegetative shading strategies, particularly in deciduous climates (during the winter, leafless trees will allow light to enter the building for warmth; during the summer, the regrown leaves will shade the building to ease the load on cooling systems).

October 3, 8AM: The two diagrams show the same result for this time period.

The way the overshadowing diagram works can be shown in the images above. On the left, we are in shade because of the immediate shadows cast (we are the red dot in the center). On the right, we are in shade because the sun is contained in an overshadowed area.

The basic overshadowing diagram is effective for point based shadow studies, but not very intuitive. It’s difficult to understand and hard to explain to others. While generated three dimensionally, it must be studied in plan, and those unfamiliar with it often visualize the surfaces as a representation of literal building shadows rather than the abstraction of a shadow range. In short, the diagram is presented radially but wants to be interpreted linearly.

To remedy this, the Rorschach Shadow diagram translates the overshadowing diagram into a basic bar graph. Rather than just overlaying a sun path diagram onto an overshadowing diagram, the Rorschach considers the hybrid of these two metrics. To generate this, sun path curves are projected onto the overshadowing diagram. The curves are then split between areas of shade and areas of sunlight. These curves are unrolled to create a bar graph showing black and white representations of shade and sunlight. The user can then control period of time to study (seasonal, monthly, weekly, daily, etc.). Other parameters can be controlled at the same time. For example, a deciduous tree’s transparency can be flexed parametrically in accordance with the day of the year.

The original Rorschach test. What do you see?

By splitting our sun paths between areas of shade and sunlight, we are also able to quantify the percentage of daylight hours that a point of interest is in the sun. This allows us to compare multiple points on our site to determine areas of maximum and minimum shading. The Rorschach metric enables us to analyze the content of the overshadowing diagram while preserving the legibility of a bar graph.

The Rorschach diagram at contrasting latitudes shows different results for the same overshadowing diagram.

Update: to download the file, please reference this post.


  • David Zeibin

    Hi Erick,

    What software are you guys using to make these diagrams? (Ecotect?)


  • ekatzenstein

    Hi David,

    The diagrams are made in Grasshopper (a plugin for Rhino). The sun data is gathered using the DIVA for Grasshopper sun vector component.


  • Steve


    Do you have any plans to make this available for use?

    Thank you!


  • ekatzenstein

    Thanks for your interest everyone. We’ve uploaded a file to the post below. Enjoy!

  • Maria

    Dear Erick,

    Thank you for the definition. It is amazing, I only have one question, how did you get from the grasshopper to the drawing? How did you bake it?

    Thank you,