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Survey intersection calculator: forward, resection (Snellius–Pothenot) and distance intersection

Choose the intersection type, enter the control points and observations — the calculator finds point P, checks it and draws a diagram.

Angles in degrees, minutes, seconds: 33°37′20″ or 33 37 20. Forward: β₁ is the angle at A between AB and AP, β₂ at B between BA and BP. Resection: clockwise angles at P from A to B and from B to C. Left/right — where P lies looking from A to B.
Calculate

Forward intersection

γ = 180° − β₁ − β₂, AP = b·sin β₂ / sin γ, α_AP = α_AB ∓ β₁, then the direct problem.

Distance intersection

Angles by the law of cosines; two solutions, choose the side.

Resection

Two angles at P to three control points define two circles; their second intersection is P. Fails on the danger circle.

FAQ

Forward intersection vs resection?
Forward: angles measured at the known points. Resection: the instrument is at the unknown point.
What is the Pothenot problem?
Three-point resection: locate a point from two angles measured at it to three known points.
What is the danger circle?
The circle through the three control points; a point on it cannot be resected uniquely.
Best intersection angle?
Between 30° and 150°, ideally near 90°.
Why two solutions in distance intersection?
Two circles meet at two points symmetric about the baseline.