(vlax-curve-getDistAtParam ename parameter)
The vlax-curve-getDistAtParam function calculates the length of the section of an entity between its start point and the point which has the specified value of the parameter.
ename specifies the entity to be evaluated.
parameter specifies the parameter value of the point on the specified entity as floating-point number.
The function returns a floating-point number representing the distance. If the function fails, it returns nil.