Coordinate transformation control report: what to record for ED50, TUREF and WGS84 delivery
If you deliver transformed coordinates, final numbers are not enough. The receiver needs source datum, target EPSG, transformation method, control residuals and field notes.
Field takeaways
- A transformation report should list source CRS, target CRS, EPSG code, units and vertical reference separately.
- Control residuals are the most important part when ED50 source data is involved.
- KML targets WGS84 geographic coordinates, while DXF often expects projected metre coordinates.
- If residuals exceed tolerance, record the risk instead of hiding it.
- Keep layers, notes, photos and exports together in MapLab Survey.
Why report a transformation at all?
When the transformation is done, the job feels finished: the point arrived, the line sits, the file opens. The questions start after delivery, when someone opens the same data in another program or lays it over an old sheet: "Is this TUREF or WGS84? Was it converted from ED50? Which parameters?" The report answers those questions in advance. It does not have to replace a formal geodetic adjustment report — it carries the source, the method and the control trail, which is exactly what circulating data between subcontractor, municipality, site and office needs.
The minimum fields
- Source system: the datum, projection and unit the data came in — e.g. ED50 / TM33, metres.
- Target system: the delivered CRS and EPSG — e.g. TUREF / TM33, EPSG:5255.
- Method: institutional parameters, grid transformation, or a fit over shared control points.
- Control differences: the E, N, Z residuals at the common points.
- Risk note: old sheet, imagery offset, too few control points.
ED50 data deserves the fullest report
HGM's ED50-TUREF transformation study shows the result depends closely on the number of points, their distribution and the method. Loading modern GNSS confidence onto every line that came out of ED50 is wrong; the report should be able to say "this data was transformed, and the source sheet's own precision must be judged separately". And never hide the control residuals — a small difference builds trust, a large one is an early warning, and in field reality early bad news beats a late surprise.
One measurement, four formats, four notes
A KML/KMZ delivery usually targets WGS84 geographic coordinates; a DXF recipient usually expects projected metres; GeoJSON runs longitude-latitude on WGS84; and CSV carries no CRS at all inside the file. When the same survey produces all four, each file gets its own coordinate note.
The habit that makes it painless
Keep transformed data on its own layer in MapLab Survey, name the control points separately, and add photos and notes. Next to the export, drop a short text: source CRS, target EPSG, date, crew, control points used, remaining differences. A small note — and the delivery suddenly reads as professional work.
Try these steps on your own phone.
MapLab Survey handles RTK/GNSS point capture, drawing, area and volume calculations and coordinate conversion, then exports to DXF, KML/KMZ, GeoJSON, Shapefile, GeoPackage, NCZ or CSV. Capture, calculation and export work offline. Live NTRIP corrections and online basemaps need a connection.
Frequently asked questions
Is a transformation report always mandatory?
Not always formally, but it is a strong professional delivery habit.
Should residuals be shown?
Yes. They define the limits of the delivered data.
What about CSV?
CSV does not carry CRS reliably, so include EPSG and units in notes.
Technical references
The field guidance in this article is aligned with the technical and official references below.
Related: ED50 to TUREF · Exporting field data to CAD/GIS · Field survey checklist · MapLab Survey