Road mapping in Brazil with mapKITE confirms high accuracy with minimal ground surveying

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The Rodovia Raposo Tavares (SP-270, SP, Brazil) has cradled a new mapKITE mapping mission, carried out by ENGEMAP and jointly computed with GeoNumerics: results confirm mapKITE as a cm-level accurate 3D corridor mapping method.

Castelldefels (Spain) and Assis (SP, Brazil), 8 January 2019. ENGEMAP and GeoNumerics have finalized the accuracy evaluation of a mapKITE mission conducted on the SP-270 motorway (Rodovia Raposo Tavares, SP, Brazil) on 25 May 2018. The goal of the evaluation was to confirm the advantages of the mapKITE method and its Kinematic Ground Control Point (KGCP) concept over the “conventional” corridor mapping method in a typical operational mapping scenario. As expected, 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-km long road segment was selected and populated with a set of 37 evenly distributed, signalised, 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 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,– resulting in similar accuracy results; i.e. 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. While the conventional method resulted in

μEN = 17, μh = 26, σEN = 26, σh = 44 and RMSEN = 32, RMSh = 51

the mapKITE one delivered

μEN = 26, μh =-20, σEN = 22, σh = 48 and RMSEN = 34, RMSh = 52

where units are mm and where we note that the mapKITE configuration uses only 4 GCPs (2 at each end of the road segment) in contrast to the 23 GCPs of the conventional one.

The mapping campaign was conducted with a SENSORMAP’s SMM terrestrial mobile mapping system and a UAVision’s UX Spyro drone equipped with a GNSS dual-frequency receiver, a Sony α7R camera with a 25 mm camera constant lens. Nominal flying height of the drone was 120 m above ground resulting in 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 (USA 9477230, ES 201231200) 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 (1) a terrestrial mobile mapping system (land vehicle and sensors) carrying (2) an optical metric target on its roof, (3) a drone aerial mapping system and (4) 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 –images, 3D point clouds– method. MapKITE combines the advantages of mobile land-based (manned) and aerial drone (unmanned) mapping systems.

GeoNumerics (Castelldefels, Spain) is a research and development (R&D) intensive small-and-medium-enterprise (SME) company specialised in geomatics and accurate navigation. MapKITE is an invention of GeoNumerics.

ENGEMAP (Assis, SP, Brazil) is one of the largest and oldest mapping companies in Brazil. It has more than hundred 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.