Clothoid constant defined incorrected in 4.2.2.2.3

[RickBrice]

Problem The clothoid constant is defined incorrectly in 4.2.2.2.3

The constant is defined as $\sqrt{L}$. The parameterized clothoid equation in 8.9.3.19.1 would then result in X and Y values with units of $Length^{0.5}$. The same is true for the arc length equation.

Solution(s) Revise 4.2.2.2.3 to say

A clothoid segment is based on the IfcClothoid where the value for the clothoid constant is specified as $\sqrt{LR}$ where L is the length measured from the inflection point and R is the curve radius at L.

$\sqrt{LR}$ is the correct equation for the clothoid constant and it will have units of $Length^{1.0}$. See https://pwayblog.com/2016/07/03/the-clothoid/

Also recommend adding the equation of the clothoid constant $A=\sqrt{LR}$ to 8.9.3.19.1

Require schema changes?

• yes
• ✓ no
• don't know

Require documentation changes?

• ✓ yes
• no
• don't know

[evandroAlfieri]

@peterrdf is it indeed a mistake in the documentation?