HIGH-TECH RTK – PPK DRONES: WINGQUAD 3
When carrying out large-scale geospatial information surveys, some important factors should be taken in consideration, such as the type of project that we are going to carry out, the equipment that will be used, scope and technical specifications of the equipment, methodology to be used, necessary personnel, budget, delivery times, among others; all this in order to carry out a correct planning of our work and to achieve the desired results efficiently.
One of the main advantages of using the PPK system is that it does not require placing ground control points or photogrammetric support points (GCP), which allows to inspect much larger areas, map large territories or places that are difficult to access.
The RTK - PPK system used by our Wingquad drones is a system of Chinese origin called Emlid, this company has perfected the manufacture of high precision RTK - PPK systems both to be used on the ground, as well as to incorporate them into UAVs.
The equipment used for this study is Emlid RS +, used as a base antenna that will be used later for data post-processing, and Emlid M +, which functions as a rover or mobile antenna incorporated into the drone's computer and connected to the sensor that is being used at that time.
The configurations and management of the equipment is carried out from a mobile application called Reach View which allows us to establish all the necessary parameters for data collection, such as frequency and band, data collection mode, visualize the status of information gathering, logging, configurations of the base station in manual mode, which allows us to place a known coordinate, or in single mode which collects information that must be processed later, and allows configuring the parameters of the rover antenna located in the drone, which must be processed in a specific software once the drone flight is finished.
Reach Rs + Technical Specifications:
Reach Rs + Reach M + is a single band GNSS receiving antenna, used for surveying, mapping and navigation issues.
- Allows to be used as a GNSS base station
- 1 cm Precision 8 GB Storage
- File formats: DXF, GeoJSON, ESRI Shapefile and CSV
- Transmit corrections over the network via NTRIP / TCP or LoRa radio.
Reach M + Technical Specifications:
Reach M + is a single band GNSS receiving antenna, which is incorporated directly into the drone to make positional corrections. It is an ideal equipment when you want to work within a short baseline as it has a baseline of up to 20 km. in PPK (Post-Processed Kinematic) mode.
- RTK mode
Up to 10 km.
- PPK mode
Up to 20 km
- Time to fix
- RINEX logging update rate
Up to 14HZ
Reach M + works with other Reach receivers over any link and are compatible with any other receiver that supports RTCM3 and NTRIP.
It is important to take into consideration the sensor to be used, since at a higher resolution you must fly higher so that the camera works correctly and can take the data at a functional time interval, with a sufficient overlap depending on each project.
Depending on our location, it is important to determine the satellite constellation systems that provide coverage to our area in order to have reception from as many satellites as possible.
Let it be 1hz, 5hz, 10hz, 14hz. The enabled constellations are listed below:
• GPS + GLONASS + GALILEO + SBAS + QZSS at 1 Hz
• GPS + GLONASS + QZSS at 5 Hz
• GPS + GALILEO at 14 Hz
• GPS at 10 Hz
The Post-Processed Kinematic (PPK) method is an alternative technique to Real Time Kinematic (RTK). When applying this method in the information surveys, the correction will be made later, as it is not done in real time. However, both the ground base and the rover (usually placed on a UAV) must record GNSS data simultaneously. In the case of the base, information can be obtained to process it later or in turn locate the base antenna on a known coordinate, on the other hand, the rover obtains raw data, which is later processed in a software called RTKLIB to receive an adjustment. precise positioning.
The RTKLIB data prost-proccessed software contains several useful modules to convert information to other standard formats such as Rinex 3.0, U-blox, among others. It incorporates modules for the processing and plotting of data where we can interpret the results and know how accurate our results are.
Using the PPK in drones:
When using the PPK system in Ummanned Aerial Vehicules -UAV several factors must be taken into account such as:
- Depending on the type and characteristics of the sensor to be used, a correct flight planning must be carried out, taking into account parameters, among the main ones are: flight height, drone flight speed, overlap and sidelap, sensor shutter speed .
- It is recommended to place some support points in the field or GCP for data verification known as check points.
A disadvantage of this methodology is the correct synchronization of a camera and Reach M +, because there can be a delay between the shooting of the camera and the actual moment the photo is taken. When a drone is flying at high speeds, the autopilot receives position readings only every several meters, which is not sufficient for the work objective when surveying.
The solution that Reach (M +) gives us is that it incorporates a cable that connects to the camera's shutter. The time of each photo is recorded with a resolution of less than a microsecond, which means that during PPK, you receive coordinates of exact moments of each photo taken.
As a result of the drone mapping, using the PPK methodology with Reach Rs + and M +, a set of images is obtained that is downloaded directly from the sensor's SD memory, and a text file that contains a list of precise coordinates corresponding to each photo. . Finally, we export all this information to a photogrammetric processing software such as Pix4dMapper that will allow us to obtain results such as Orthomosaic, Elevation models, contour lines, 3D models such as point clouds, among others.
In order to carry out a verification and experimentation of the appropriate methodology to apply the Emlid RTK - PPK system using Wingquad professional drone technology, several flight tests were carried out applying different data collection parameters. Several flights were established at a height of 150 and 200 meters; Likewise, the rover antenna was configured at a frequency interval of 14hz, 5hz and 1hz, finally establishing that for the type of sensor used (42 MPX) it is advisable to fly at a minimum height of 200 meters, and use the highest number of constellations of satellites at a frequency of 1 hz.
1. Selection of the study area
As a study area, the eastern zone of Quito was selected, a land located in Lumbisí where constant flight tests are carried out under the proper safety standards.
2. Estimation of the work equipment and tools to be used
Once the study area has been analyzed, work planning begins, estimating the personnel that will be involved and the necessary tools to use.
For our case study, 3 technical engineers needed to carry out the work were taken into account.
- 1 pilot and 1 co-pilot
- 1 person in charge of GNSS data collection and information processing.
Said personnel were in charge of the placement of the base station in the field to obtain the base coordinate using GNSS Emlid Reach Rs + equipment, which has been adjusted and corrected previously.
Additionally, the technical team of pilots was in charge of flight planning, configuration of the GNSS rover antenna located on the drone, and flight execution.
And a person in charge of data processing and generation of results such as: point cloud generation, orthomosaic digital surface model, digital terrain model, contour lines, and digitization and generation of plans.
Likewise, the necessary tools to use in the project were determined.
A GNSS equipment Emlid Reac Rs + and Emlid Reach M +, single-band, were used, with which the positional corrections of the data collected by the drone were obtained.
On the other hand, a VTOL-type fixed-wing drone called Wingquad 3 was used, which has the ability to collect information in an area of up to 350 ha. per flight, with a flight autonomy of 60 minutes. The drone was fitted with a 42 mega pixel Sony RGB sensor.
3. Work Plan
The flight planning was carried out in the planning program in 2D and 3D called AirRails of the company UAVenture, where the relative flight height was estimated at 200 meters, the sensor to be used of 42 Megapixels and the strategic point from where we made the flight .
Once the terrain in question has been recognized, the work plan estimated and the necessary tools selected, the survey is carried out in the field.
First, we go to the study area in order to take the GNSS base coordinate in the field.
In turn, the rover antenna settings were established at 1 hz as follows:
By having greater coverage of constellations of satellites under the frequency or data collection interval of 1 HZ, it was evidenced that the same amount of information obtained from both the rover antenna of the drone was obtained compared to the images captured by the sensor
On the other hand, two drone flights were made in the Lumbisí sector, at a height of 200 meters relative to the ground, with a Sony RGB sensor of 42 MPX, through which a GSD (Ground Sample Distance) of 2.74 cm / pixel.
4. Office data processing and results generation
Once the field work was finished, the information was processed, both the data obtained with the GNSS equipment and the images obtained with the drone.
In the first case, the coordinates obtained were processed with a control point processing software called RTKLIB, based on a known point located on the main road near the flight area.
As can be seen in the previous image, by using the plot module of the processing software, we can check the accuracy of the data obtained and its processing.
Photogrammetric Processing Results:
In the same way, the image processing was performed with the Pix4D Mapper photogrammetric processing software.
The procedure to enter the processed data of our PPK system in drone is as follows:
1. The project must be created in Pix4dmapper.
2. Once the project is created, the images are entered into the software.
3. Enter the text file generated from the coordinate processing with the RTKLIB software.
4. Perform information processing in the Pix4dMapper software.
The obteined results are showed next:
- Point cloud in LAS format. It was obtained:
Number of 3D densified points: 24117405
Average density (per m3): 102.2
- Orthomosaic in GEOTiff format with a resolution of 2.78 cm / pixel.
- Digital surface model in GEOTiff format with a resolution of 2.78 cm / pixel.
- Digital terrain model in GEOTiff format with a resolution of 13.69 cm / pixel.
- Contour lines in shp format with an interval of each meter.
When carrying out the verification and experimentation of the appropriate methodology to apply the Emlid RTK - PPK system using Wingquad professional drone technology, several flight tests were carried out applying different data collection parameters. Several flights were established at a height of 150 and 200 meters; Likewise, the rover antenna was configured at a frequency interval of 14hz, 5hz and 1hz, finally establishing that for the type of sensor used (42 MPX) it is advisable to fly at a minimum height of 200 meters, and use the highest number of constellations of satellites at a frequency of 1 hz.
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