In our example, we assume the Pitrex default coordinate space of (-18000, -24000) to (18000, 24000)

By having the user adjust the corners of a rectangle individually, so that the rectangle fills the
screen and looks correct, we get coordinates for the distorted corners as

(-17050,-24560), (19000,-23750), (18800, 24007), (-18101, 23976).

Plugging these into the maths and generating a transformation matrix, we transform the
following intended coordinates to the actual coordinates that we'll use when drawing:


intended(-18000,-24000) transforms to actual(-18920.4,-23412.3)
intended(-9000,-24000) transforms to actual(-10055.2,-23615.1)
intended(0,-24000) transforms to actual(-1116.55,-23819.7)
intended(9000,-24000) transforms to actual(7896.36,-24025.9)
intended(18000,-24000) transforms to actual(16984.5,-24233.9)
intended(-18000,-12000) transforms to actual(-18661.7,-11352.1)
intended(-9000,-12000) transforms to actual(-9845.7,-11504.4)
intended(0,-12000) transforms to actual(-957.209,-11658)
intended(9000,-12000) transforms to actual(8004.72,-11812.8)
intended(18000,-12000) transforms to actual(17041,-11968.9)
intended(-18000,0) transforms to actual(-18405.8,572.339)
intended(-9000,0) transforms to actual(-9638.6,469.477)
intended(0,0) transforms to actual(-799.681,365.774)
intended(9000,0) transforms to actual(8111.84,261.219)
intended(18000,0) transforms to actual(17096.9,155.802)
intended(-18000,12000) transforms to actual(-18152.8,12363.3)
intended(-9000,12000) transforms to actual(-9433.82,12308.8)
intended(0,12000) transforms to actual(-643.93,12253.9)
intended(9000,12000) transforms to actual(8217.76,12198.4)
intended(18000,12000) transforms to actual(17152.1,12142.6)
intended(-18000,24000) transforms to actual(-17902.6,24023.1)
intended(-9000,24000) transforms to actual(-9231.33,24015.9)
intended(0,24000) transforms to actual(-489.926,24008.6)
intended(9000,24000) transforms to actual(8322.48,24001.2)
intended(18000,24000) transforms to actual(17206.8,23993.8)