Site Plan by Drone – How It Works

What is a Site Plan?

A site plan is a scaled, georeferenced representation of a property and its immediate surroundings. It shows buildings, property boundaries, access roads, terrain structures and relevant topographic features in a defined coordinate system – in Germany, standardly ETRS89/UTM.

In construction planning, three main variants are distinguished: the simple site plan is an extract from the official cadastral map (ALKIS) showing only cadastral data without field survey. The detailed site plan supplements this base data with current terrain information, elevation points and building status. The official site plan is a legally binding document for building permits, which may only be prepared by publicly appointed surveyors (ÖbVI) or cadastral offices.

Drone photogrammetry falls in the category of detailed and documentary site plans: it provides highly accurate, georeferenced survey and planning foundations used in preliminary design, inventory documentation and as planning basis – but does not replace an official site plan in the sense of state building codes.

Official vs. Digital Site Plan – The Key Boundary

The most common question about drones and site plans is: Can I replace the official site plan for a building permit with a drone image? The clear answer is: No – at least not alone. In Germany, the official site plan for a building application must be produced by a publicly appointed surveyor (ÖbVI) and bear a professional seal. This monopoly is regulated nationwide in the state surveying and building codes and applies to modern surveying methods as well.

However, what the drone can do excellently: it provides current, accurate inventory data on the basis of which an ÖbVI can produce the official site plan faster and more cost-effectively. Many surveying offices therefore use drone data as efficient input for their own planning work. At the same time, the digital drone site plan has independent, considerable value for all planning phases before the building permit: preliminary design, property analysis, setback verification, visualization and tender documents.

Workflow: From Drone to Finished Site Plan

Creating a digital site plan from drone images follows a standardized photogrammetry workflow. This consists of five steps that – depending on the area and desired resolution – can be completed within a working day.

Coordinate System and Georeferencing

Correct georeferencing is the foundation of a usable site plan. In Germany, since 2010, the coordinate system ETRS89/UTM (European Terrestrial Reference System 1989, Universal Transverse Mercator projection) is mandatorily used. Germany lies in UTM zones 32N (western part) and 33N (eastern part). The geoid model for heights is DHHN2016, with mean height deviations of approximately 1.0 cm.

RTK drones connect via the SAPOS network (satellite positioning service of German state surveying offices) or a local CORS reference point directly to the coordinate system. The result: every pixel of the orthophoto has a known, georeferenced position in ETRS89/UTM – without manual ground control points. For the highest requirements (positional accuracy < 2 cm), the use of at least 3 ground control points (GCPs) measured with precision GNSS is recommended.

Accuracy and Scales

The achievable accuracy of a drone site plan depends on three factors: the drone and camera (sensor quality, focal length), the flight altitude (GSD) and the georeferencing method (RTK, PPK or GCP). The following values are practical for typical building and property surveys in Germany:

Without georeferencing (no RTK, no GCPs), the result is unusable for planning purposes. With RTK support alone (without GCPs), positional accuracies of ±3–5 cm and height accuracies of ±3–8 cm are realistic. With RTK and at least 3 well-distributed GCPs, an absolute positional accuracy of ±1–2 cm and height accuracy of ±2–3 cm is achievable.

Use Cases: Who Benefits from a Drone Site Plan?

Architects and planning offices use the digital drone site plan as a basis for preliminary and schematic design (HOAI service phases 2–3). The decisive advantage: the orthophoto provides not only floor plan information, but also the current construction status, tree positions, terrain structures and access situations – all in one georeferenced dataset.

For property developers, the drone site plan is a cost-effective decision basis before engaging an official surveyor: property size, buildability, setback distances and boundary clearances can already be reliably estimated from the orthophoto and DXF.

Municipalities and area managers use georeferenced orthophotos and digital site plans for urban planning, land use planning procedures and GIS-based inventory recording.

Output Formats and Software

A professionally created drone site plan typically includes several complementary output formats covering different planning and documentation purposes:

Costs and Time Advantage

Costs for a digital drone site plan depend on property size, required accuracy and scope of delivery. As a rough guide: residential properties up to 1,000 m² can be processed from approx. €290–390 (including orthophoto and DXF). Commercial properties up to 5,000 m² typically cost €490–890. For larger areas from 1 ha, individual daily rate calculations apply.

Compared to classical field survey with total station and leveling device, the drone method saves considerable time: what a survey team captures in half a day, an RTK drone covers in 20–45 minutes. The subsequent automated photogrammetry processing takes 1–4 hours. The complete result is typically available within 24–48 hours of the flight.