Aerial imagery for engineering and geodetic surveying and complex cadastral works

Aerial surveying with UAVs significantly reduces the cost of topographical and cadastral plans production due to the reduction in the amount of field work. Helicopter-type drone is able to capture from 20 to 50 hectares per flight, depending on the scale of the survey, aircraft type drone - up to 2000 hectares. However, it should be noted that the technology does not completely replace the work of a surveyor or cadastral engineer in the field. The amount of ground-based fieldwork for UAV shooting depends on the nature of the object and the underlying surface - from several control points in the launch area to the GCP network with the density of 4-5 points per square kilometer. In any case, the amount of field work compared to tradirional survey is reduced by 3-5 times.

General work order

  • Obtaining permits for the use of airspace and conducting the aerial survey
  • Installation of the ground control points (GCPs)
  • Aierial image capturing
  • Processing of GNSS measurements, calculation of coordinates of image centers, verification of results with control points
  • Photogrammetric processing - construction of an orthophoto, digital surface model, digital terrain model (under certain conditions), 3D terrain models, point clouds
  • importing data into AutoCAD
  • mapping and vectorization of the orthophotomaps, obtaining elevation marks from the digital elevation model
  • Field verification and additional survey using satellite geodetic measurements (if necessary)
  • Topographic plan of a given scale production

Сompilation survey

It is the determination of the coordinates of the temporary base station and control points in the local coordinate system. The points of the state geodetic network are used as the starting points of the compilation survey. For 1 square kilometer of survey at a scale of 1: 2000, 2-3 GCPs are installed, for a scale of 1: 500 - 5-6 GCPs. During the flight, the base station is installed at a point with known coordinates.

 

UAV aerial survey

For the maximum economic effect of the survey it is necessary to use high-performance drones with the maximum possible characteristics of the camera and an integrated satellite geodetic receiver. At Aerostream we use industrial drones - Geoscan 101, Geoscan 201, Geoscan 401. For the small objects we use our own quadroopter Aerostream 001 with an integrated Sony RX-1 camera. The accuracy of the final product is up to 10 cm horizontally and vertically. The RMS of the detailed survey is 1-2 cm.

Usually it takes 10-15 minutes to prepare UAV for take-off.

To prepare the flight task, it is necessary to indicate survey boundaries, the ground resolution of the imagery (cm / pixel), the overlaps, and the point of landing. Flight planning is usually done in office and is adjusted on the spot according to the situation. Below is the interface of the GeoscanPlanner.

 

Aircraft-type drones launch from a catapult, copters take off from any level ground. The video below shows the launching of UAVs and the use of obtained materials for cadastral borders monitoring and volume control.

GNSS Measurement Processing

After the flight, pictures and a log from the GNSS receiver are downloaded. The next step is obtaining the exact coordinates of the image centers.

All our drones are equipped with dual-frequency or single-frequency geodetic class satellite receivers. During the flight, the on-board GNSS receiver logs the coordinates and the event of the camera shutter release. The data is captured at a frequency of 10 Hz. A high degree of synchronization between the camera and the receiver allows to get timestamps at the exact moment when the shutter actually worked. The GNSS received data is processed along with the data of the base station and the data of the reference stations (if available). As a result of post-processing the accuracy of the image centers coordinates is usually a few centimeters horizontally and vertically.

 Photogrammetric processing

Is performed in Agisoft Photoscan Pro or similar sofrware. The geodetic coordinates of the photographic centers are used as initial data. Ground points are used for control.

Orthophoto example

Dense cloud example

The results of photogrammetric processing

orthomosaic in geotiff, jpg, Google Earth KML formats. Single file or in tiles.
Digital Surface Model as a height map in TIFF/BIL/XYZ formats. Individual buildings and vegetation could be excluded, if necessary

Photogrammetric point cloud in TXT (XYZ point cloud), LAS, DXF formats. A point cloud of any density could be generated.
Contour lines at a given step based on a dense point cloud. In any GIS format of in DXF.
Scales available: 1:500, 1:1000, 1:2000

Topographic plan creation using aerial photography materials

  • importing orthomosaic in AutoCad
  • obtaining of elevation marks from a height map, importing marks in AutoCad
  • mapping and vectorization of the orthophotomaps
  • field verificarion, survey of elements that are not visible on aerial photography materials
  • final topographic plan production

Orthophotomosaic is imported into AutoCad, where vectorization is performed with interpretation of topographic survey objects. The contours of lands, fences, engineering structures, buildings and other visible elements of the topographic plan are plotted.

 

From the digital surface model (height map) height points are extracted in a txt format and imported into AutoCad.

After the field inspection and surveying of the elements that are not visible on aerial photographs, the cartographer performs a "clean" drawing according to the requirements for topographic plans.

 

CONCLUSIONS

— Aerial survey reduces the time spent on field work by 70-90 percent, depending on the complexity of the topographic survey site, which makes the cost of work significantly lower.
— Data processing work is not significantly increased, and the quality of the final product is improved.
— The accuracy of the received materials matches or surpasses the work performed by the classical methods of topographic and cadastral surveys.