At a glance
In order to use drone photogrammetry data in surveying and GIS projects, you need to properly fit a drone raid into a geodetic system. In this guide, SkySnap shows you step-by-step: selection of CRS (PUWG/ETRS), application of GCP / RTK / PPK methods, raid planning, data processing and quality control (RMS, checkpoints). At the end, you’ll find FAQs and a PDF checklist to help you prepare your next survey missions.
Choice of coordinate system (CRS) in Poland
The first step is to decide which coordinate system you want to work in. In Poland, the most common is:
- PUWG 1992 (EPSG:2180) – for large areas,
- PUWG 2000 – in zonal versions (EPSG:2176-2180) for local projects,
- ETRS89 / WGS84 – in global and GIS applications.
This layout should be established prior to GCP measurement so that all GNSS data is consistent with the project’s target CRS.
GCP, RTK, PPK – when which solution?
GCP (Ground Control Points).
These are physical points with known coordinates that are used to georeference images and models.
✅ Advantages: highest accuracy, error control, compliance with GUGiK requirements.
⚠️ Requires GNSS measurement and good visibility of points in images.
RTK (Real-Time Kinematic)
The drone receives real-time position corrections from the VRS network or its own base station.
✅ Advantages: fast workflow, no need to measure GCP.
⚠️ Requires a stable data connection.
PPK (Post-Processed Kinematic).
GNSS data is corrected after the flight, combining the drone and base station logs.
✅ Advantages: high accuracy without in-flight connectivity.
⚠️ Requires processing in dedicated software and time synchronization.
SkySnap recommendation:
For work requiring centimeter accuracy (e.g., heap surveying, earthwork), use PPK or RTK with several GCPs for inspection.
Planning the raid
Good planning is half the battle.
- Image coverage: a minimum of 70-80% longitudinal, 60-80% transverse.
- Flight height: match the GSD resolution (e.g., 2-3 cm/pix).
- Conditions: avoid high lighting contrasts and winds above 5 m/s.
- Safety: check airspace restrictions (PAŻP, Droneradar).
- GCP: spread evenly – in the corners and in the center of the area.
Establishment and measurement of GCPs – good practices
- Number of points: min. 5-10 GCP for small areas, more for large areas and varied terrain.
- Visibility: contrast markers, clearly visible from the planned height.
- Measurement: GNSS RTK/PPK receiver with registration of coordinates in the CRS of the project.
- Documentation: record the method, measurement time, correction network name and RMS error.
Data processing in photogrammetric software
- Import photos: upload photos with EXIF metadata or PPK logs.
- Add GCP: enter coordinates and CRS (e.g., EPSG:2180).
- Alignment (bundle adjustment): match the model to the GCP.
- Export: orthophotomap (GeoTIFF), point cloud (LAS/LAZ), NMT/DSM in target CRS.
Quality Control (QC)
To make the data reliable, perform:
- Checkpoints: measurement points not used in alignment – used to verify accuracy.
- RMS analysis: check the mean residual error (Root Mean Square) – for geodetic data usually ≤2-3 cm.
- Error map: check the direction and displacement vector – you will detect possible rotations or CRS errors.
The most common mistakes and how to avoid them
| Error | Effect | How to avoid |
|---|---|---|
| CRS incompatibility | Displacement of the entire model | Always declare CRS in project and export |
| Not enough GCPs | Orthophoto deformations | Add points at corners and center |
| Error in PPK logs | Systematic offset | Always save GNSS logs and database data |
| Poor lighting conditions | Blurry photos, SfM errors | Fly in even light and no wind |
SkySnap workflow – from plan to finished product
- We establish CRS and accuracy requirements with the customer .
- Raid planning (coverage, grid, GCP location).
- GCP measurement with a GNSS receiver (RTK or PPK).
- Performing a drone raid with GNSS log recording.
- Data processing in photogrammetric software (PPK + GCP).
- QC report: RMS, checkpoints, metadata.
- Provision of finished files: GeoTIFF, LAZ, DXF.
FAQ: fitting a drone raid into a geodetic layout
What is the difference between RTK and PPK?
RTK sends correction in real time, PPK corrects data after the flight. PPK is more flexible, RTK is faster in the field.
How much GCP do I need?
Usually 5-10 points for smaller projects, more for large ones. Add some checkpoints for quality control.
In which CRS to work in Poland?
Most commonly PUWG 1992 (EPSG:2180) or PUWG 2000. Choose according to customer requirements.
Does RTK/PPK preclude GCP?
No. In practice, several GCPs are recommended even for RTK/PPK flights – for control and improved accuracy.
How to check the accuracy of the model?
Compare the checkpoint coordinates with the model. An RMS of less than 3 cm indicates a very good fit.
Download GCP + QC checklist (PDF)
👉 Download free checklist
Includes a ready-made template for checkpoint planning, measurement and data quality control.
Do you need support?
Chcesz, aby Twój nalot był w pełni zgodny z układem PUWG 1992 lub 2000?
Skontaktuj się ze SkySnap — pomożemy w:
✅ planowaniu nalotu,
✅ pomiarze GCP,
✅ obróbce RTK/PPK,
✅ i przygotowaniu raportu QC.
Free E-book
Learn how to prepare a mission step-by-step, avoid raid mistakes and create accurate orthophotos and 3D models. The perfect guide before your first commercial assignments.
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