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Coordinate to Chainage and Offset Calculator

Project a point onto a straight baseline to obtain its absolute chainage, signed offset and perpendicular foot coordinate.

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Use a straight two-point baseline and verify its direction before interpreting the signed offset.

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Projection limitation: This projects onto an infinite straight baseline. Confirm the baseline direction, chainage datum, offset sign and whether the perpendicular foot belongs on the intended segment.

What the projection means

The target coordinate is projected at right angles onto the infinite straight line through the two baseline points. The distance along that line becomes chainage, while the perpendicular distance becomes offset.

chainage distance = (Point − Start) · unit-line
signed offset = (Point − Start) · left-normal

Left and right offsets

Positive is left and negative is right when looking from baseline start towards baseline end. The result also gives the exact foot coordinate on the baseline, which can be useful for checks or CAD construction.

Frequently asked questions

Can the perpendicular foot lie outside the baseline?

Yes. The calculator treats the baseline as an infinite line and warns when the foot lies before the start or beyond the end segment.

Why is my offset sign opposite to another system?

Software packages use different conventions. This tool defines positive as left looking from baseline start to end; reverse the baseline or negate the offset when matching a different convention.

Does elevation affect the result?

No. This is a two-dimensional plan calculation using Easting and Northing only.