Tool 05 · Localization

Fit a local system
onto the one that counts.

A Helmert fit onto control points, returning rotation, scale and shift together with RMS and per-point residuals. Plus a grid ↔ ground factor, so you know how far a projected distance sits from the real one on site.

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2 tools in one
2 min. control points
5 cm warning threshold
GeoKantar — localization, Helmert fit to control points
Tool

Two tools in one place

Localization handles an arbitrary local system; grid ↔ ground handles the gap between the projection plane and the actual ground.

Helmert fitPoint pairs: a source coordinate (GPS or local system) and a control coordinate (known)
Minimum pairsTwo — each additional pair yields residuals and an RMS
ParametersRotation, scale (also in ppm) and shift
Quality controlRMS and per-point residual; anything over 5 cm is flagged red
Applying itAny source coordinate is immediately recomputed into the control system
Grid factor (GSF)The projection's effect on distance, for the chosen system and position
Elevation factor (EF)The effect of height above the ellipsoid
Combined factor (CSF)GSF × EF — the overall ratio of grid to ground distance
ConverterType a grid or ground distance; the other is computed with that factor
Procedure

How to use it

01

Enter control point pairs

For each point, give the source coordinate (what you measured) and the control coordinate (the true, known value for the same point).

02

Look at the parameters

With at least two pairs you get the rotation, scale and shift that best fit the source points onto the control points.

03

Check RMS and residuals

RMS shows the overall fit; the residual shows how far each point deviates. Red means over 5 cm — that point is suspect.

04

Apply it to a coordinate

Once the fit looks right, type any source coordinate below and read it back in the control system.

05

Switch to grid ↔ ground

For a chosen system, position and height you get the CSF, and the distance converter then works in both directions.

Details

Why this matters

When to use localization

When you are working in an arbitrary local system — a site grid, an old report, a network someone laid out with no tie to the national system. A Helmert fit ties that system to known points.

What a residual tells you

A residual is how far one point deviates once the fit is computed. If every point has a small residual except one, that one is usually mistyped or its marker has moved — the fix is to check that point, not to add more.

Grid is not ground

A projection distorts distances, and height changes them again. At 500 m elevation and well away from the central meridian, the difference over a kilometre runs to several decimetres — enough to throw out a long stakeout.

When to use grid ↔ ground

When you are working in an official system (Gauss-Krüger) and need the real distance you will measure on site with a tape or EDM, rather than the computed one from coordinates.

Questions

Frequently asked questions

How many control points does localization need?

At least two, which is enough to solve rotation, scale and shift. With three or more you also get residuals and an RMS, so you can judge how good the fit is.

What does a red residual mean?

That the point deviates by more than 5 cm from the fit. The usual cause is a mistyped coordinate or a disturbed marker, rather than a bad transformation.

What is the combined scale factor (CSF)?

The product of the grid factor (projection effect) and the elevation factor (height effect). It converts a grid distance from coordinates into the true ground distance and back.

Is this the same as coordinate transformation?

No. Coordinate transformation moves between defined systems with known parameters. Localization derives the parameters from your own measurements, for a system that has no official definition.

Get GeoKantar

This tool ships inside the GeoKantar app. Available on the App Store and Google Play.

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