FMB sketch calculation online — enter G-line notation and bend cutting points with offsets to calculate distances along the line, to endpoints, or diagonally between bends. Pair with the links to feet converter or RSR & FMB area error adjuster.
How to useHow It Works
1. Enter G-Line
Provide the G-Line notation (e.g. AB) and the total distance along the line.
2. Add bends
For each bend, enter the cutting point distance, offset, and direction (right or left). At least one bend is required.
3. Calculate & visualize
Choose the distance type, click calculate, then export results or visualize the bend geometry on a diagram.
How to Calculate FMB Sketch Measurements
G-Line and cutting points
Every FMB sketch is drawn along a G-line (baseline). Each bend is marked at a cutting point (chainage along the G-line) with a perpendicular offset to the left or right of the line.
Distance formula
For a bend at chainage x with offset y, place it at coordinates (x, y) on the G-line. Distance between two bends uses the Pythagorean theorem:
d = √[(x₂ − x₁)² + (y₂ − y₁)²]
Start-to-bend and bend-to-end distances use the same formula from the G-line endpoint (0, 0) or end point.
FMB area calculation
This tool computes linear distances along bends. For total plot area from an FMB sketch, triangulate the boundary polygon or use the land area calculator. When RSR area differs from plotted FMB area, use the RSR & FMB area error adjuster.
Corrections & questions
These guides are maintained for practising AP surveyors. If a step is outdated or wrong, tell us — we prioritise field corrections.
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