XGRIDS Pro Guide™ / Module 4: Positioning

4.6 Coordinate Systems and Datums

The coordinate system configuration in LixelStudio determines whether the output point cloud is in the right place in the world. Operators who are not surveyors by background often find this the most confusing part of georeferencing. This page covers what you actually need to know to configure it correctly.

Section 1

Core Concepts

You do not need a surveying background to configure coordinate systems in LixelStudio, but you do need to understand four terms and what they refer to.

Ellipsoid

A mathematical model of the shape of the Earth used as the reference surface for coordinates. Different countries and coordinate systems use different ellipsoids. WGS84 is the global standard used by GPS. GRS80 is used by most modern national systems. Older systems may use other ellipsoids. The RTK device records in whatever ellipsoid your CORS network transmits, you need to know which one.

Datum

A specific realization of a coordinate system, defined by both an ellipsoid and a set of control points that tie the ellipsoid to the actual Earth surface. WGS84, NAD83, and ETRS89 are datums. Two systems can use the same ellipsoid but be different datums because they are anchored differently. WGS84 and GRS80 are mathematically nearly identical, but WGS84 and NAD83 are not, coordinate positions in the same area can differ by over a meter depending on which you use.

Projection

A mathematical transformation that converts curved geographic coordinates (latitude and longitude) into flat planar coordinates (Easting and Northing). All projections introduce some distortion. UTM is the most commonly used global system. State Plane, local grids, and national systems all have their own projection definitions. LixelStudio outputs to projected coordinates, you must specify the target projection for the output to be in the correct system.

Helmert Transformation (Seven Parameters)

When the source datum of your RTK corrections is different from the target datum of your output, a coordinate transformation is required to convert between them. The Helmert transformation uses seven parameters: three translations (X, Y, Z offsets), three rotations (around each axis), and a scale factor. These parameters are specific to each datum pair and region, they must come from an authoritative geodetic authority for your area, not from estimation.

Section 2

What the RTK Module Records

The XGRIDS RTK module records latitude and longitude coordinates, geographic coordinates in the ellipsoid of your CORS network. It does not record Northing and Easting in a projected system. This is important because it means the projection step happens in LixelStudio during processing, not in the field. Your job in the field is to confirm which ellipsoid the CORS network transmits in. Everything else is configured in software.

If your NTRIP provider is not listed in the LixelGO dropdown, select Custom, then set the ellipsoid to match your CORS network. If the ellipsoid is also not in the list, select Custom and enter the semi-major axis value (a) and inverse flattening ratio (1/f) manually. These values are published by the geodetic authority for your coordinate system.

Section 3

Supported Projection Types in LixelStudio

LixelStudio currently supports four projection types for coordinate output. Most projects outside Mainland China will use UTM or Transverse Mercator.

Projection Type

Common Use

EPSG Reference

Gauss Kruger (3-degree zones)

China national grid (CGCS2000, Beijing 54)

Zone-specific EPSG codes

Gauss Kruger (6-degree zones)

China national grid, some legacy European systems

Zone-specific EPSG codes

UTM

Global standard, construction, surveying, most non-China projects

EPSG 326xx (north), 327xx (south)

Transverse Mercator

National grids (UK, Australia, Japan, local systems)

System-specific EPSG codes

Look up the EPSG code for your target coordinate system at epsg.io. The EPSG record provides all the projection parameters you need to enter in LixelStudio: central meridian, false easting, false northing, latitude of origin, scale factor, and the associated ellipsoid.

Section 4

Scenario 1: Same Source and Target Ellipsoid

This is the simpler case. Your CORS network transmits in WGS84, and your required output is also WGS84-based (such as UTM WGS84). No datum transformation is required, only projection.

In LixelGO, set the RTK type and ellipsoid to match your CORS network. In LixelStudio, set the source coordinate and source ellipsoid to match what you configured in LixelGO, set the target coordinate and target ellipsoid to your required output system, and enter the projection parameters from the EPSG record. No seven parameters are needed.

Section 5

Scenario 2: Different Source and Target Ellipsoids

This scenario requires Helmert transformation parameters in addition to the projection. It occurs when your CORS network transmits in one datum (for example WGS84) but the required output coordinate system uses a different ellipsoid (for example JGD2011 for Japan, or KGD2002 for Korea).

In LixelStudio, after setting the source and target coordinate systems and ellipsoids, you will be prompted to enter the seven Helmert transformation parameters. These must be obtained from the official geodetic authority for your region. They cannot be calculated from EPSG records alone, you need the specific parameters published for the datum transformation pair in your area.

Example: WGS84 to JGD2011 (Japan)

Set RTK type to Custom, ellipsoid to WGS84 in LixelGO. In LixelStudio, set source to WGS84, target to JGD2011. Set target ellipsoid to GRS80 (fixed automatically for JGD2011). Enter Japan Plane Rectangular projection parameters from EPSG (e.g., EPSG:6677 for CS IX). Import seven-parameter file for the WGS84 to JGD2011 transformation.

Example: Custom Ellipsoid (GRS67)

If your CORS network transmits in GRS67 (used in parts of South America), it will not appear in the LixelGO dropdown. Set type to Custom, ellipsoid to None, then enter your host and mountpoint. In LixelStudio, set source and target ellipsoid to Other and enter the GRS67 parameters: semi-major axis 6,378,160 m, inverse flattening 298.25.

Section 6

Finding Your Parameters

Projection parameters: look up the EPSG code for your target system at epsg.io, the record lists all projection parameters needed for LixelStudio input
Ellipsoid parameters (semi-major axis and inverse flattening): published by the geodetic authority for the coordinate system. Also available via EPSG records for standard ellipsoids
Seven Helmert transformation parameters: obtain from the national geodetic authority for the target datum, or from official datum transformation documentation. Do not use parameters from unofficial sources, small errors in these values produce systematic offsets across the entire dataset
If unsure of your CORS network's datum: contact your NTRIP provider directly and ask which ellipsoid and datum their network transmits in. This is standard information they will have available
For most projects outside Mainland China: WGS84 source ellipsoid, UTM target projection, same-ellipsoid scenario (Scenario 1). Look up your UTM zone from the EPSG zone index and enter the parameters directly

Coordinate configuration understood. Final page in Module 4: the hybrid approach that combines RTK and GCPs for the highest accuracy achievable with the XGRIDS platform.

The Hybrid Approach →