Area calculation bug with arcs


#1

Although Sketchup calculates the true lengths of arcs it does not calculate the true area of faces where part or all of the perimeter is made up of arc(s). Instead it uses the straight segments that are used to depict the arcs.

Open the entity window. Add a circle. Select the face to see its area.
Now select the circle edge. Change the number if segments by a lot.
Now select the face again. The area has changed!!!

This is not technically a bug. It was just lazy design.
There are applications where exact true area are very important.

I’ve started to write a ruby script to do it correctly. It’s not that hard to do.
But it shoul be corrected in the product.


#2

It seems like a matter of ontology :stuck_out_tongue: . An arc or circle is really a collection of edge segments with some metadata that remembers it came from an arc or circle. So which calculation is correct? One based on what it really is, or one based on how it was created? I think the real issue is consistency. Pick one or the other and stick with it!


#3

I think ontology and user expectations are on my side.
The Sketchup model actually includes an arccurve object which can be “exploded” into line segments. Its not just remembering how it was created.
This curve remains a curve object even if scaled into an elipsoid.
Select it and you get true arc length, not the length of the display segments.
A polygon perimeter can consist of both line and arc segments.
If you want the faceted area you can always explode the curve.
But is you relly need the actual area you should be able to get it.

Building parcel surveys are often defined by both straight bearings and tangent arcs. Because of zoning coverage limits, its crucial to have true area of the parcel…