More intuitive Spline Fillet behaviour

[dswahn]

A lot of 3ds max users who work with spline profiles expect Fillet operations to yield a fillet that corresponds to a segment of a circle with a radius of the specified value. A fillet value of 25cm should always produce a curve that fits a 25cm radius circle, as long as the original spline allows it that is.

The current way 3ds max does fillets is to affect the size of the fillet based on the angle. It means only 90° angles will give you the correct fillet radius. Obtuse angles gives you too large, and acute angles gives you too small.

The image below shows the current result on the left, and on the right how most users expect the fillet to behave:

Most engineering drawings define fillets this way, so it makes very much sense to have 3ds max behave the same way. It's much more practical and intuitive.

What I suggest is that such new fillet behaviour becomes an optional setting, in case users want to use the classic mode.

The calculation required to correct the fillet is fairly simple, assuming we need to adjust the current input value:
(fillet value) / (tan (knot angle/2)
So "fillet value" is your desired radius, and the "knot angle" is the angle between the selected knot and its adjacent knots, or the positions a very small distance away from the knot along the spline (which would support non-linear knot types). 

Until this is implemented, users who wish to convert fillets to always provide a radius segment can evaluate the following expression in the MAXScript Editor, it will automatically put the converted value into your clipboard for pasting as the new fillet value. Just change the desired radius and knot angle:
setclipboardText (units.formatValue ((units.decodeValue "25cm") / (tan (45.0/2))))
This expression works for Chamfer values too!