We have analysed the formula from buildingSMART: on-line documentation:

"The circular arc is described by (see figure 1):

• R = signed Radius, if IsConvex = true, then -R, if IsConvex = false, then +R as length measure

• s0 = StartDistAlong as length measure

• z0 = StartHeight as length measure

• g0 = StartGradient as ratio measure

•

The following equations are used for the centre of the circular arc:

center (distance along) sc = s0 - R * s0 / sqrt(1 + g0^2)

center (height) zc = z0 + R / sqrt(1 + g0^2)

The following equations are used for any point along the circular arc:

at any point s1 along the HorizontalLength

height (IsConvex = TRUE) z1 = z0 + sqrt(R^2 - (s1 - sc)^2)

height (IsConvex = FALSE) z1 = z0 - sqrt(R^2 - (s1 - sc)^2)

gradient g1 = - (s1 - sc) / (z1 - zc) "

The formula for sc must be wrong because s0 is in meter while the other element (R*S0) in the formula is in m2 - or?