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Chainage and Offset to Coordinate Calculator

Calculate a point coordinate from a straight baseline, an absolute chainage and a signed perpendicular offset.

Enter your data

Confirm both baseline points, the chainage datum and the signed offset convention before calculating.

No sign-in
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Positive = left; negative = right, looking from baseline start to end.
Inputs are processed in this browser. This calculator does not send project data to a server.
Alignment limitation: This uses an infinite straight baseline. Confirm the chainage datum, baseline direction, signed-offset convention and intended segment limits.

Offset convention

This calculator uses the common signed convention: a positive offset lies to the left when looking from the baseline start point towards the end point. A negative offset lies to the right. Enter zero to calculate a point directly on the line.

How the coordinate is calculated

The baseline vector is converted to a unit vector. The chainage difference is applied along that vector, then the offset is applied along the left-hand perpendicular vector.

P = Start + unit-line × (target chainage − start chainage) + left-normal × offset

Worked chainage and offset example

Take a baseline from E 500000.000, N 200000.000 to E 500100.000, N 200000.000, with chainage 100.000 at its start. A target at chainage 140.000 and offset +5.000 m is 40.000 m along the eastbound line and 5.000 m to its left. The calculated coordinate is therefore E 500040.000, N 200005.000.

This simple east–west case is useful as an independent sign check: looking east, left is north. For an arbitrary baseline the calculator rotates the same along-line and perpendicular components into Easting and Northing.

Chainages outside the segment

The mathematical line can be extended before the start or beyond the end. The result clearly warns when the requested chainage is not inside the two-point segment.

Frequently asked questions

Is the target chainage measured from zero?

Not necessarily. Enter the chainage assigned to the baseline start. The calculator subtracts it from the target chainage to obtain the distance along the line.

What happens with a negative offset?

A negative offset places the point to the right looking from the baseline start towards its end.

Does this support curved alignments?

No. This initial calculator uses a straight two-point baseline. Curved alignment and transition geometry require additional alignment data.