What is the easiest way to cut off a segment of a circle?

[PVousden121]

Hi,

I have a problem in that I have a circle and a triangle as defined by my data such that the triangle is made up of the centre of the circle and two points on the circumference as shown below:

So, if I overlay the shapes as shown above it forms 3 distinct areas the main part of the circle shaded pink, the triangle shaded white (or not shaded might be more accurate), and then the smaller segment of the circle that I have shaded yellow.  What I am looking to have as a result is the area of the circle minus the yellow segment which means that it will consist of the pink and white areas.

Is this possible without resorting to advanced maths and creating arcs etc....  I am not confident enough with the spatial processing tool's capabilities to not dismiss that there is just this functionality hiding somewhere within the capabilities of Alteryx.  Or perhaps as part of the Formula functionality.

Any help or pointers gratefully received.

Peter  

 

[CharlieS]

Hmm, the perfectly straight line does present a problem, but that could potentially be built for. The real problem is: once you cut the circle in half, how would you decide which side to keep? my assumption is that you're using the water side of the polygon, but the workflow doesn't know that without some additional information about landmass. Something to think about. 

[PVousden121]

There is a rule for identifying which side and is based on the smallest angle to the points - this is provided in another field that I didn't which defines whether it is clockwise or counter-clockwise and in this case, it is clockwise from the western-most point - 

No 2 51.6375 -4.83667

So, in this case the arc is to the north which I have just realised and contrary to what I provided earlier.

Would it be easier if the 'circle' point used for this aspect was 'moved' to form another triangle so that your previous solution would work again or can you cut a circle in half?

Thanks as always,

Peter 

[CharlieS]

I think it would be more reliable to move the center point in these cases since the direction would have to be determined anyways.