📐 Your phone in the field: surveyors and architects
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A smartphone doesn't replace a total station or an RTK GNSS receiver. Used well, though, it's an excellent tool for reconnaissance, quick surveys and site documentation. You just need to know its limits.
1. Phone GPS accuracy: what you need to know
- In open sky, a smartphone is usually accurate to a few meters (often around 3 to 5 m).
- Dual-frequency (L1 + L5) phones are noticeably more accurate, especially in cities. Check your model's specifications.
- Accuracy drops near buildings, trees, in valleys and indoors (signal reflections).
- To improve measurements:
- turn on high-accuracy location (allow Wi-Fi and Bluetooth for location);
- wait 30 to 60 seconds without moving before recording a point;
- average several readings if the app allows it;
- check the satellites in view and the reported accuracy with an app like GPSTest.
👉 For cadastre, setting out or boundary work, use an RTK receiver. Many external receivers connect to the phone over Bluetooth and replace its position (through "mock location" in developer options).
2. Coordinate systems: the most common mistake
The phone gives coordinates in WGS 84 (latitude and longitude, code EPSG:4326). Your plans often use a local projection:
| Country / use | Common system | EPSG code |
|---|---|---|
| World, GPS | WGS 84 | 4326 |
| Mainland France | RGF93 / Lambert-93 | 2154 |
| Morocco (north) | Merchich / Nord Maroc | 26191 |
| Many countries | UTM (zone depends on longitude) | 326xx (north) |
⚠️ Mixing two systems can shift your points by hundreds of meters. Always write the system and EPSG code in your exports.
3. Measuring with the camera (augmented reality)
AR measuring apps are handy for quick estimates (a room, an opening, ceiling height), but:
- accuracy depends on light, surface texture and distance;
- always check with a tape measure or a laser meter before ordering or building anything.
4. Site photos that are actually useful
- Turn on photo geotagging and make sure the phone's time is set automatically.
- Take a wide photo (context), then a close-up (detail).
- Put a reference object (tape measure, ruler) in the frame to keep the scale.
- Sort photos by project and date the same evening.
5. Exchange formats to know
| Format | Use |
|---|---|
| CSV | List of points (X, Y, Z, code) |
| KML / KMZ | Google Earth |
| GPX | GPS tracks and waypoints |
| GeoJSON | GIS, web |
| DXF / DWG | CAD (AutoCAD and others) |
| Shapefile (SHP) | GIS (QGIS, ArcGIS) |
6. In the field
- Bring a power bank and a spare cable: GPS and a bright screen in the sun drain the battery fast.
- Download offline maps of the area before you leave.
- Back up your surveys every evening (cloud or computer).
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