3D cm achieved with UAV/van mapping system MapKITE

All photos: GeoNumerics

All photos: GeoNumerics

Kinematic Ground Control point for UAV photogrammetry: A dynamic duo of UAV and mobile van combine to deliver the accuracy of conventional methods with only 2+2 ground control points at the ends of the corridor.

By Ismael Colomina, Pere Molina and Roberto da Silva Ruy

A Brazilian and a Spanish company, ENGEMAP and GeoNumerics respectively, have finalized the accuracy evaluation of a mission conducted with the latter’s mapKITE technology on a Brazilian motorway in 2018.

The goal of the evaluation was to confirm the advantages of the mapKITE method and its kinematic ground control point (KGCP) concept over conventional corridor mapping methods.

The mapKITE and the conventional method delivered comparable accuracy results — the difference being that the latter requires a dense set of surveyed ground control points (GCPs) while mapKITE does the job with almost no GCPs.

For this purpose, a 4-kilometer segment of the Rodovia Raposo Tavares in São Paulo state was populated with a set of 37 evenly distributed, signalized, accurately surveyed ground points. The set was divided into two subsets of 23 GCPs and 14 ground check points (GChPs) — the ground truth — respectively. The 4-km road segment was also covered by 189 drone images and their corresponding 189 KGCPs. The image set was processed as a conventional aerial corridor block:

  • with the integrated sensor orientation (ISO) method in a 23 GCP + 14 GChP configuration, and
  • as a mapKITE aerial corridor block in a 4 GCP + 14 GChP + 189 KGCP configuration.

The two processes produced similar accuracy results: mean (μ), empirical standard deviation (σ) and root mean square (rms) error of the photogrammetric determination of the horizontal (EN) and vertical (h) coordinates of the GChPs against the ground truth. (All units are stated in millimeters.)

The conventional method delivered: μEN = 17, μh = 26, σEN = 26, σh = 44 and RMSEN = 32, RMSh = 51.

The mapKITE method delivered: μEN = 26, μh =-20, σEN = 22, σh = 48 and RMSEN = 34, RMSh = 52.

The mapKITE configuration uses only four GCPs (two at each end of the road segment) in contrast to the 23 GCPs of the conventional method. Nominal flying height of the drone was 120 meters above ground, producing an average ground sampling distance (GSD) of 2.3 cm. Forward image overlap was 80% resulting in a base-to-height ratio of 0.157.

MapKITE is a GeoNumerics patented method for 3-dimensional corridor mapping that combines the two latest geodata acquisition methods, terrestrial mobile mapping and aerial drone-based mapping. MapKITE is a tandem terrestrial-aerial mapping method and system composed of:

  • a terrestrial mobile mapping system (land vehicle and sensors) carrying
    • an optical metric target on its roof;
    • a drone aerial mapping system; and
    • a real-time virtual tether and post-mission software.

In a mapKITE mission, the drone follows the land vehicle, and thus the vehicle target becomes a kinematic ground control point visible and measurable on each image. It is a high-accuracy, high-resolution Earth observation method. MapKITE combines the advantages of mobile land-based encompassing images and 3D point clouds. MapKITE combines the advantages of mobile land-based (manned) and aerial drone (unmanned) mapping systems.

GeoNumerics (Castelldefels, Spain) is a research and development company specializing in geomatics and accurate navigation.

ENGEMAP (Assis, Sao Paolo, Brazil) is one of the largest and oldest mapping companies in Brazil. It has more than 100 employees, three aircraft, two mapping land vehicles, a number of rotary- and fixed-wing drones and a record of accomplished mapping and cadastral projects. ENGEMAP is officially authorized by the Brazilian Ministry of Defence (MD) and the Brazilian Department of Airspace Control (DECEA) to conduct mapKITE commercial flights in Brazil.

MANUFACTURERS

The mapKite campaign was conducted with a Sensormap SMM terrestrial mobile mapping system and a UAVision UX Spyro drone equipped with a NovAtel OEM2 GNSS dual-frequency receiver with a Maxtena antenna and a Sony α7R camera with a 25-mm camera constant lens. The INS/GNSS system in the Terrestrial Vehicle was a Span-CPT (Novatel) including dual-frequency antenna and DMI wheel sensor.


ISMAEL COLOMINA is chief executive and chief scientist at GeoNumerics. He has a Ph.D. in mathematics from the University of Barcelona.

PERE MOLINA is advanced applications program manager at GeoNumerics. He holds a master’s degree in mathematics from the University of Barcelona and a master’s in photogrammetry and remote sensing from the Institute of Geomatics, Catalonia.

ROBERTO DA SILVA RUY is technical manager at ENGEMAP. He has a Ph.D. from the Universidade Estadual Paulista.

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