Expertise
For a large area or land with difficult access, a drone can produce an orthophoto and a digital terrain model. But it is not the right solution for every site: we will tell you frankly whether it is for yours.
The principle
Photogrammetry consists of reconstructing the geometry of the land from photos taken from several angles. The drone flies over the site following a flight plan that ensures sufficient overlap between the images; software then computes a point cloud, an orthophoto (a rectified image that can be overlaid on a plan) and a digital terrain model (DTM).
These products are only as good as their fitting. Before the flight, we place clearly visible ground control points, which we measure by GNSS and tie to the Lambert system. It is these points that place the orthophoto and the model at the right coordinates and the right elevation; other points measured on the ground are used to check the result.
The firm only flies a drone when the extent or access of the site warrants it, with the required authorisations, obtained by the firm. Most of our surveys are still carried out with GNSS and total station: see our Topographic plan page.
When the drone is useful
Over several tens of hectares, the drone covers in one flight what would take long days of ground survey, and the orthophoto shows tracks, buildings, crops and visible boundaries at a glance.
Agricultural or rural land →Embankments, quarries, riverbanks, uneven ground: the drone measures what can only be covered on foot at the cost of risk or a great deal of time.
A dense DTM makes it possible to calculate earthwork or stockpile volumes and to compare two states of the same site at different dates.
A recent, georeferenced image serves as a background for studies, general plans and geographic databases (GIS).
Mapping and GIS →When it is not the right solution
The drone is not a superior method in itself: it is one more tool. In several cases, a ground survey is more accurate, simpler or quite simply mandatory.
How the assignment works
The steps of our method, with a preliminary question: is the drone justified?
Area, relief, vegetation, use of the result, expected precision. We choose the method — drone, ground survey or a combination of both — and explain why.
Deliverables, estimated time for our work, flight plan and check of the authorisations required for the site.
Placing and GNSS measurement of the ground control and check points, then the flight. Areas the drone cannot see properly are surveyed on the ground.
Photogrammetric processing at the office, comparison with the check points measured on the ground, then production of the orthophoto, the DTM and the plans.
We hand over the files and a report stating the tie-in points and the discrepancies observed.
Deliverables
Precision, timescales and cost
The precision of a drone survey depends mainly on the quality and distribution of the ground control points measured by GNSS, the flight height, the quality of the images, the relief and the vegetation. We do not publish a general figure: the check report states the discrepancies actually observed on your site.
The timescale and cost depend on the area, the relief, access, the number of ground control points, flight conditions, the products requested and the share to be supplemented on the ground. We do not publish rates (why). To check a slope or a volume, our free Surveying calculations tool can help.
Frequently asked questions
Not as the only source. Property boundaries are established and measured on the ground, boundary markers included, according to the applicable procedure. The orthophoto can supplement the file, not replace this work.
Not always. On a large open area, it saves time on site; on a small plot, the preparation, ground control points and processing cost more than a ground survey. The quote compares the two when the question arises.
Poorly. Under tree cover, the photos show the foliage. We then combine the flight with a ground survey for the covered areas.
Yes: the firm is authorised and obtains the required authorisations. We also check the constraints specific to the site before proposing a flight; if a flight is not possible, we propose a ground survey.
Yes, if the use allows it. We will ask you what it is for, to advise you on the appropriate fitting and level of detail.
Your site
Describe the site and its intended use: we will tell you whether the drone is the right method, and send you a written quote.