Angle of view & Centre line

Hi,

Can you help - please see attached image

Yellow Dot grid co-ordinate = 540000,320000
Pink Dot =545000, 320000
Green Dot = 544499, 317775

I would like a way of calculating the angle of the view Red lines.

Also the grid co-ordinate that is centre of the two points (Pink / Green Dot)

I would have 45 + of these calculation to do at a time,

Cheers

WCE