SDX-Cloud: Choosing the right coordinate system for a project

Summary

You choose the coordinate system during project creation in SDX-Cloud. The coordinate system is a transformation pipeline that converts global satellite coordinates into local project coordinates. For most construction and volume workflows, a projected coordinate system in meters with the correct local UTM zone is the safest starting point. Select the global datum that matches your region and correction service (e.g. ETRS89 or DBREF in Europe, NAD83 in North America, GDA2020 in Australia). Use WGS84 as a safe fallback when the correction service datum is unknown.

Introduction

This workflow helps you decide which coordinate system setup to use when you create a project. In many cases, the fastest option is a standard UTM-based preset. When the project must match local design files such as DXF or LandXML files, you may need a custom EPSG-based setup. When the project is on a construction site with a surveyor-provided calibration, you import a localization file instead.

The decision comes down to four questions: what datum your correction service delivers, which projection covers the site, how heights should be transformed, and whether the site needs a custom localization.

How coordinate systems work in SDX-Cloud

A coordinate system in SDX-Cloud is not just a label. It is a transformation pipeline that converts global satellite coordinates (latitude, longitude, ellipsoidal height) into local project coordinates (easting, northing, orthometric height).

Every pipeline breaks down into four components:

• Source datum: the global reference ellipsoid your GNSS receiver works in (e.g. WGS84, ETRS89)
• Target datum: the regional reference ellipsoid for your project (e.g. ETRS89, NAD83)
• Projection: converts latitude/longitude into easting/northing (e.g. UTM zone 32N, Austria GK West)
• Vertical transformation: converts ellipsoidal height to orthometric height using a geoid model or offset (e.g. German DHN 2016, Austrian GHA)

The horizontal (easting/northing) and vertical (height) parts are always handled separately. The projection handles X/Y, and the geoid or offset handles Z.

One project uses one pipeline. All devices on the project (SDX-Compact, GNSS rovers, drones) must share the same coordinate system for data to align.

Prerequisites

• You can create a new project in SDX-Cloud.
• You know the project location.
• You know which correction service the GNSS equipment uses and what datum it delivers (usually ETRS89 in Europe).
• You know the source system of the raw data. For standard raw drone data, this is often WGS84 / EPSG:4326.
• If client DXF or LandXML files must align with the project, you know the required local target system or EPSG code.
• If a surveyor provided a localization file (LOK, DC, CAL, or GC3), you have it ready.
• If the project requires a geoid grid file, you know which regional grid matches the project area.

Step-by-step instructions

1. Start with the project goal

1. Decide whether the project is a quick visual demo, a standard drone survey, or a construction site requiring precise alignment with surveyor or machine control data.
2. Use a projected coordinate system in meters for construction and volume workflows.
3. If a standard UTM setup is enough, continue with the preset configuration (Step 3).
4. If the project uses a surveyor-provided calibration file (LOK, DC/CAL, or GC3), skip to Step 6.
5. If client files do not align with preset options, plan to use a custom EPSG-based setup (Step 4).

Expected result: You know which setup path to follow.

2. Choose the horizontal reference (datum)

Multiple datums exist because tectonic plates move. The European plate drifts 2-3 cm per year northward, so a point surveyed in WGS84 today will have shifted by about 50 cm in 20 years. Regional datums like ETRS89 are attached to the tectonic plate so coordinates stay stable over time.

The current difference between WGS84 and ETRS89 is approximately 1.2 meters and growing (~1.7 m in 20 years).

The correction service determines your datum. In Europe, 99% of correction services (RTK Premium, TopNet, Leica SmartNet, SAPOS) deliver coordinates in ETRS89. The same applies to NAD83 in North America.

Use these rules:

1. ETRS89 → ETRS89: correct for most European projects. No datum shift applied. Use this when the correction service delivers ETRS89.
2. WGS84 → WGS84: safe fallback when the correction service datum is unknown. No datum shift applied.
3. WGS84 → ETRS89: applies a ~1.2 m datum shift. Only use this when the GNSS receiver is explicitly in WGS84 and the project must be in ETRS89. If you configure this when the receiver is already in ETRS89, all positions will be falsified by ~1.2 meters.

Expected result: You have selected the correct source and target datums based on the correction service.

3. Configure the preset setup for standard projects

SDX-Cloud includes curated presets for standardized coordinate systems maintained by government surveying agencies:

• Global: UTM zones (60 zones worldwide, each for a 6-degree longitudinal strip, differentiated by hemisphere)
• Austria: M28 (West), M31 (Central), M34 (East) with GHA geoid
• Germany: Gauss-Krueger zones with DHN 2016 geoid
• USA: State Plane systems with regional GEOIDs

To configure:

1. Start creating a new project in SDX-Cloud.
2. Open the coordinate system settings during project creation.
3. In Source System, select the datum that matches your correction service (usually ETRS89 in Europe, or WGS84 as fallback).
4. In Target System, select the local system for the site (e.g. ETRS89 / UTM zone 32N, or a national grid like Austria GK West).
5. Make sure source and target datums match the correction service to avoid an unintended datum shift.

Expected result: The project is configured with a validated preset that matches the site and correction service.

4. Use the custom EPSG setup only when needed

Use custom EPSG only when:

• The required system is not available as a preset.
• You have confirmed the exact EPSG code with the project surveyor.

To configure:

1. In the coordinate system settings, select Custom.
2. Set the horizontal type to EPSG.
3. Enter the EPSG code for the required local system.
4. Confirm the code matches the reference frame of the files you want to overlay.

Expected result: The project uses a specific local system not available in the preset database.

5. Select the vertical setup

1. Select Offset for a simple vertical shift (e.g. a demo where you need to align layers by a fixed value like 1.2 meters).
2. Select Grid File when the project needs a regional geoid model for accurate height alignment. Choose the grid file that matches the project area (e.g. DHN 2016 for Germany, GHA for Austria).
3. Review horizontal and vertical settings together before creating the project.

Geoids are raster grid files maintained by government agencies. Each cell contains an elevation shift value subtracted from the ellipsoidal height to get the local orthometric height. Geoids only affect the vertical component and do not fix horizontal datum issues.

Expected result: The vertical setup matches the project accuracy requirements.

6. Use a localization file for construction site projects

Standardized projections like UTM introduce scale distortion that increases with distance. For large construction sites where dimensional accuracy is critical (e.g. an 800 m × 300 m foundation), UTM coordinates will not produce exact dimensions on the ground.

A site localization is a custom coordinate system created by a surveyor at the start of a construction project to eliminate this distortion. It is delivered as a file:

• LOK file (Leica): contains the full transformation pipeline, human-readable
• DC/CAL file (Trimble): contains the transformation and optionally control points for validation
• GC3 file (Topcon): contains only control points; SDX-Cloud solves the transformation

To import:

1. In the coordinate system settings, select the localization file import option.
2. Select the correct file type (DC-File/CAL-File, LOK-File, or GC3-File).
3. Drag the file into the import dialog.
4. After import, review any residuals table shown (for DC/CAL with control points or GC3).
5. Small residuals (1-2 cm) are normal. Large residuals may indicate a bad control point or mismatch.

Expected result: The project uses the surveyor's site-specific coordinate system with minimal distortion.

Common failure points and fixes

• Project offset by ~80-100 cm in Europe: The source datum is set to WGS84 but the correction service delivers ETRS89. This applies the ~1.2 m WGS84↔ETRS89 datum shift. Fix: recreate the project with ETRS89 → ETRS89 (no shift).
• DXF or LandXML data does not line up: The preset does not match the local site reference. Switch to the custom EPSG-based setup with the correct code, or import the site's localization file.
• Dimensions on site don't match the design: Standardized projection distortion (UTM) on a large site. The project needs a site localization file instead of a raw UTM zone.
• Heights look wrong after import: The vertical setup does not match the project location. Check whether the project should use an offset, a specific geoid grid file, or the localization file's built-in vertical component.
• Custom EPSG code produces wrong results: The EPSG database entry does not match the intended transformation. Switch to an SDX preset if available, or have the surveyor verify the correct code and transformation parameters.

Verification

1. Review the source system, target system, and vertical setup before finishing project creation.
2. Confirm source and target datums match the correction service to avoid an unintended datum shift.
3. If using a localization file, check the residuals table for deviations.
4. Create the project only after all settings are verified.
5. After project creation, import or capture initial data and confirm it aligns as expected.

Expected result: The project opens with the correct coordinate system and data aligns to the real world.

Related articles

• Article: SDX-Cloud: Coordinatesystems
• Article: SDX-Cloud: DC-File and LOK-File Import
• Article: SDX-Cloud: Use USA GEOIDs in custom coordinate systems
• Article: SDX-Cloud: Project coordinate systems - US state planes