# Tech Chat - What is Localization in Surveying Project?

The first step of starting a surveying project is to set the coordinate systems. Normally, the surveying software will include global or country-wide systems for you to select. However, some local projects will use the local small-scale coordinate system. At this time, the general coordinate system in the software is no longer applicable, and the surveyor can transform the coordinate system through the localization function.

Localization is the process of transforming from one coordinate system to another. By establishing one-to-one correspondence between two coordinate systems.

**Localization classification**

- Transformation from one space rectangular coordinate system to another one.
- Geodetic coordinates (BLH) to space rectangular coordinate system (XYZ).

**Transformation models**

**1. Four parameters **

Four parameters model is usually used for conversion between two different space rectangular coordinate systems. It is suitable for conversion of spatial coordinates in a small range (within 5 km). There are four unknown parameters in this model:

- The translation of two coordinates (X△, Y△), the difference between the coordinates origin of two plane coordinate systems.
- The rotation Angle of the plane coordinate axis α. By rotating an angle, the X and Y axes of the two coordinate systems can be rejoined together.
- Scale factor m, that is, the length ratio of the same segment of straight line in two coordinate systems, realizes scale proportional conversion. Usually, the m value is almost 1, between 0.999 and 1.001.

**2. Seven parameters **

Seven parameters generally apply to geodetic coordinates (BLH) to space rectangular coordinate system (XYZ); it is suitable for the transformation of spatial coordinates in a large range of measurement area (up to 15 km), which requires at least 3 common known points. Because there are more known points, the coordinate accuracy of seven parameters conversion is higher than that of four parameters conversion, but the operation is more complicated than that of four-parameter conversion.

There are seven unknown parameters in the seven-parameter model, namely:

- The translation of three coordinates (X△, Y△, Z△), namely, the coordinate difference between the origin of two spatial coordinate systems.
- The rotation angle of the three coordinate axes (ϵX, ϵY, ϵZ)). By rotating the three coordinate axes in order to specify the Angle, the (X, Y, Z) axes of the two space rectangular coordinate systems can be rejoined together.
- Scale factor K, that is, the length ratio of the same segment of straight line in two spatial coordinate systems, realizes scale proportional conversion. Usually K is almost equal to 1.

**General requirements for selecting known points**

- The four parameters model has no less than 2 known points, and the seven parameters model has no less than 3 known points.
- Known points should cover the whole conversion area.
- Known points should be evenly distributed.

**How to do Localization in SingularPad & SingularSurv software?**

1. Go to the Localization function in the software.

2. Enter at least three pairs of points to compute (for example, take K1, K2, K3 as known points and A1, A2, A3 as measured points). After click calculate, the software will calibrate automatically.

3. Click Apply to confirm to replace datum. The value of HRMS/H.Resid andVRMS/V.Resid should meet the requirements (H ≤ 0.02m, and V ≤0.02m).

Learn more about SingularXYZ field software,

https://www.singularxyz.com/SingularPad.html

https://www.singularxyz.com/SingularSurv.html