Three Point Angular Resection

Content for students.
A Three Point Angular Resection only gives as a result 2D coordinates of an unknown point an instrument is setup on, from only Horizontal Directions observed in Face Left / Face Right to three points with known coordinates.

It includes
A bit of Thales (chords and angles within a circle)
Sine Rule
Fundamental Problems in Land Surveying: Direct and Indirect (mostly known as join and polar calculation in English)
Additional

Timecodes
00:00 Intro
02:40 Graphical determination of Collin's point
03:09 First Triangle: unknown station inside or outside?
03:30 Additional Geometry derived from Collin's Point
04:48 Thales theorem of chords within a circle
06:31 Working on the Second Triangle: Determination of coordinates of Collin's Point
31:48 Working on the Third Triangle: Determination of coordinates of the unknown station
55:57 Summary