Thursday, 27 September 2012

Revit Needs to Go Back to School

Here's a simple maths problem. Take a circle of radius 10. This radius could be any unit of measurement;  millimetres,inches,light years,baby steps. To find the area of this circle, you apply the formula:


Therefore the area of our circle is 3.14159 x (10²) = 314.159

Seems simple enough?

Not according to Revit

Draw a filled region using a circle of radius 10.
Firstly, do this using metric units (mm & mm²) and you get:

Now do this in imperial units (decimal in & in²) and you get:

The metric figure is 99.98% accurate, the imperial a little closer. Big deal you may say, and in most cases you'd be correct, certainly in a small example like this. But what if I take this circle and make it bigger, then I extrude it to make some 3D geometry, then I copy this around many times, then I want to know the volume of these elements?  Small errors start to compound into more significant overall errors

pi is a constant. Revit knows this is a circle. So why the discrepancy?