# Thread: Midpoint on the elliptical arc

1. ## Midpoint on the elliptical arc

Hi,
I want to find the midpoint on the elliptical arc

I know the following
1 Start point of elliptical arc
2 End point of elliptical arc
3 Center Angle of elliptical arc or Sweep Angle
4 Center point of elliptical arc
5 Major radius of elliptical arc
6 Minor radius of elliptical arc

Angle (in radian) =StartAngle + (CenterAngle / 2)
Where strat angle is the angle from center point to start point in radian

MidX = CenterX +Cos(Angle) * Distance
MidY = CenterY+ Sin(Angle) * Distance

Distance is the Distance from center point to MidPoint on the elliptical arc which is unknown.

Please do help in finding the Distance which is unknown or specify some other approch to do so.

I have tried by substituting the major radius and minor radius as X and Y Distance, but its not giving correct result.

Thanks

2. can you post a drawing of what you are doing
might be easier for us to answer
and label the elements...

3. ## Mid point on elliptical arc

Originally Posted by bigwave
can you post a drawing of what you are doing
might be easier for us to answer
and label the elements...

I have attached the sample picture.

Actually my elliptical arc may be horizontal(fig 1) or vertical(fig 2) or rotated (fig 3) as shown in sample picture

For Fig 1, I have provided the point details.

A = Start Point = ( 170.6004 , 159.3217)

C = End Point = ( 196.1697 , 129.754)

O = Center Point = (206.7051 , 146.6791)

Center Angle = 283

Start Angle = 161 ( Angle form center point to start point)

End Angle = 283 ( Angle from center point to End point)