Visualizing the Spherical Dome Calculator

Original online dome calculators.

The original online dome calculators for spherical and half oblate ellipsoid domes.

Eighteen years ago, I wrote the first dome calculator for our website. I’d used the formulas before in spreadsheets, pattern programs, and even a script for the Palm Pilot. Writing the little program in the new web language of Javascript was fun. We still use it today, but it’s showing its age. The old calculator doesn’t work well on phones, and it has a dated, turn-of-the-millennium style. We have a new website; it is time for a new calculator.

Like before, the first calculator should be for the spherical dome—the most common shape in dome construction. What else do we want from the calculator? It should work on smartphones, tablets, laptops, and desktops. It should include more calculations and present them more clearly. We want to add units like feet and meters. And it should also do more to help users understand what the numbers mean—it needs to draw a picture.

The old calculator page had a static image of a dome with labels for the various measurements. That helped a little. What we want is a dynamic drawing based on the calculator input and output. For new dome enthusiasts, it would help clarify the shape and size of the dome. For experienced users, it would give an at-a-glance confirmation they input the numbers correctly.

Spherical dome calculator conceptual sketch.

A sketch of the concepts that went into the new spherical dome calculator.

Dave South

Could the drawing be more helpful in understanding the scale of the structure? We talked about this a lot. Could we add a line at six-feet above the floor to show the headroom for a person? Yes, but it would take time to understand what the line represents. What about adding a person to the drawing? That was a great idea. The silhouette of a person would instinctively show the size of the structure. Could the person be scaled correctly if the dome is in feet or meters? If we could add a person to scale, could we add a car? What about a basketball court?

The old calculator couldn’t save the results. The numbers had to be input every time, or we would take a screenshot. Could we save the results of this calculator? If the new calculator could draw an image of a gym with a basketball court, could the drawing and calculations be emailed to a potential customer? How about a button to copy results to the clipboard? We could paste the answers into our notes, CAD drawings, or emails.

Eventually, the answer to all these questions was yes. Web browsers have come a long way since 2002. They support inline drawings via Scaled Vector Graphics. We could save the calculator inputs as part of the page URL, which meant that every possible dome calculation could have its own “page” on our site. There are simple tricks to allow a “Copy to Clipboard” button. And finally—with a lot of trial and error—I was able to add a person, then a car, and eventually a basketball court—at scale.

Try out the Spherical Dome Calculator. It includes detailed instructions along with several real-world examples.

Now I’ve been told asked to get working on the Half Ellipsoid Dome Calculator.

Finished calculator.

The finished spherical dome calculator — complete with basketball court.