Perform the technical survey service via area using a 1:1000 scale drone for the area of the exploration platforms.
Place 6 milestone landmarks type B
Place 40 photogrammetric support points in the field using dual-frequency GNSS equipment.
Carry out the topographic survey through the use of drones under the standards established by the regulatory entities of information and cartography Military Geographical Institute at a scale of 1: 1000.
Generate results such as: point cloud, orthomosaic, digital terrain model, digital surface model, contour lines with 1 meter interval.
Georeferenced information was collected under the SIRGAS Reference System, WGS84, UTM projection, zone 18 South.
To carry out the topographic survey, the stages were divided into 2 work phases, a field phase where the Geodetic Network points, photogrammetric support points were placed and the drone flight was carried out to collect the information, and an office phase where the information processing and generation of results was carried out, which are detailed below:
The field phase had two stages, the first where the Geodetic Network points and landmarks were placed, and photogrammetric support points, which lasted 4 days, and the second stage, which lasted 2 days. The 6 drone flights were carried out to collect information. For these purposes, parameters such as:
Visual recognition of the study area to observe aspects such as the shape of the terrain, relief, accessibility to the study area, weather conditions, among others.
-Determination and analysis of sites for the placement of the 6 control points in the field by using a precision GPS of double frequency according to the static and fast static method.
6 milestone construction planning with type B monumentation established by the Military Geographic Institute.
Type B cairn construction
Implementation of milestones and data collection
Implantation of RTK points (Real Time Kinematic for its acronym in English) through the use of a precision GPS of double frequency according to the static and fast static method and placement of tarps or objects visible from the air, which will serve as support points to perform photogrammetric processing with high positional precision, and to achieve a correct reconstruction of the information.
Placement of photogrammetric support points
-Establishment of the limit of the study area, since it will serve as the basis for the respective flight planning.
Making flight plans with the Air Rails planning software.
Execution of flights with VTOL Wingquad 3 hybrid drone which will follow the flight plan previously made. The flights were made at a height of 150 m above the surface.
Preparation of the drone for flight
The office phase lasted 7 days, which was divided into: 5 days of information processing and 2 days of editing.
-The processing of the control points obtained in the field by means of precision GPS was carried out in order to be used in the model for their adjustment in orientation, scale and precision using the software, taking as base points the network TAL points of the REGME.
-Before the images were processed in the office, they were verified and approved in the review program, otherwise, the flight must be run again with the necessary corrections.
-After the information was collected in the field, the captured images were sent to the office or to the cloud, where they were processed using photogrammetric processing software.
-Once the results were executed in the photogrammetric processing software, they went through a detailed review.
-The results were edited and approved.
-Delivery of results, delivery of report, and all the information in the same file in digital format as a backup of the work carried out together with all the expected results of the product.
Precision GNSS equipment:
The 5 s, 220 channel, double frequency GNSS equipment was used. You can use more GNSS, satellite and signal constellations than traditional GPS. It provides better precision even under the leaves of trees or buildings, more productivity in field work.
Flight Execution: Drone Wingquad 3
For the execution of the flight, the VTOL Wingquad 3 type drone was used with a flight autonomy of approximately 60 minutes, a 24 MPX Sony sensor and various optimal technical characteristics to carry out the desired work.
Drone used in information gathering
Wingquad 3 drone technical specifications
PIX4D Mapper information processing software:
PIX4D Mapper is software that allows photogrammetry with UAVs or drones, which generates from images, obtained from the air, high-end orthomosaics with metric quality, DSM (digital surface model), DTM (digital terrain model) , contour lines, and point clouds, with a fully automatic workflow
It also allows reconstruction of network infrastructure and volume calculation.
Pix4D Mapper Photogrammetric Processing Software
The following results were obtained:
Results of the survey of control points or photogrammetric support points.-
The survey of 6 geographical landmarks with type B monumentation of the study area was carried out. These points were raised with a GNSS equipment referring to the UTM coordinate system, ITRF08 horizontal datum, SIRGAS vertical datum, Ellipsoid GRS80, Reference epoch 2016.4. Likewise, 40 more points were determined as photogrammetric support. Monograph of checkpoints and milestones with photographic evidence
Photogrammetric support points
40 support points were surveyed. These points were raised with a GNSS equipment referring to the UTM coordinate system, ITRF08 horizontal datum, SIRGAS vertical datum, Ellipsoid GRS80, Reference epoch 2016.4
FLIGHT PLAN AND IMPLEMENTATION
The flight was made with the Wingquad 3 drone with a 24MPX RGB camera.
A total of 6 flights were carried out, distributed in 2 flights of 265.88ha and 33.56ha respectively, and 4 additional flights of 113.61ha, 229.10ha, 216.15ha and 183.10ha respectively. The flight plan was programmed at a relative height of 180 meters in order to guarantee the desired resolution or GSD of 5cm / pixel, with a constant speed of 16m / s, the average flight time of each mission was 55 minutes. As a result, images were obtained at a resolution or GSD (ground sample distance) of 4.41 cm / pixel. Overlap of 65% lateral and 75% frontal due to the presence of abundant vegetation, it is recommended to use a not so high overlap.
The following images shows the flight planning:
Results of the survey of control points or photogrammetric support points
The information processing was performed by entering geo-located images, each with its x, y and z coordinate (longitude, latitude and height), referring to the SIRGAS reference system, WGS94, UTM projection, zone 18 South.
A 3D point cloud was obtained in .LAS format. An average of 16937 points per image were generated, obtaining a density of 24.16 points per m3.
Point cloud classified into 5 categories
An Orthomosaic in Geo TIFF format with a GSD (Ground Sample Distance) of 4.43 cm / pixel was generated.
The DSM or Digital Surface Model in Geo TIFF format was generated with a GSD (Ground Sample Distance) of 4.43 cm / pixel.
Digital Surface Model or DSM
The DTM or Digital Terrain Model in Geo TIFF format was generated with a GSD (Ground Sample Distance) of 22.14 cm / pixel.
Digital Terrain Model or DTM
Equidistant level curves were generated at 1 meter.
The information processing in the PIX4D Mapper software allowed us to determine the confidence level of the reconstruction of the information, obtaining a percentage of 97% of the calibrated images, with an average reprojection error of 0.18.
By: María Gabriela López
Geographical Engineer & Environmental Management
LAS Technical Coordinator & Sales Engineer
For more information visit: www.latitudeas.com
Phone: +1 347 960 6444