Extract from above article – Approved drone/sensors for photogrammetry
Other equipment required:
It is best to perform the topographical mapping when there is no crop cover. We always ask the crop types that are present in the different fields and confirm with the client which months we should avoid.
For sparse vegetation (stand-alone trees, bushes etc.) present on-site during the study, our methodology allows us to extrapolate, confidently, surrounding data to represent the ground obscured by the canopy. The point cloud data is classified into multiple categories (ground, low vegetation, high vegetation etc.) to ensure that the most representative data is being used when generating the grid of levels and Contour Lines presented in the CAD deliverable.
Finally, if we must collect data when there are standing crops present, we can also process the data and “remove” the crops with an algorithm, by interpolating known “ground points” (visible from the drone data) and creating a Digital Terrain Model.
Generally, photogrammetry will be the best option for projects that require visual and engineering data over larger scales as it provides high quality data at a reasonable price. Drone-based LiDAR has advantages for surveying narrow structures such as power lines or telecom towers, and in cases where it is important to get good ground elevation data below certain vegetation types (see previous section).
Given the additional costs of capturing and processing LIDAR data, one is well advised to only deploy where necessary and to consider it as a complementary methodology to photogrammetry, not a substitutive one.
Photogrammetry is a solution which we increasingly see in the solar industry. Photogrammetry is the process of combining 1000s of RGB images to create a 3D point cloud which is especially useful for recovering the exact positions of surface points. There are many uses for the data. It can be used to show terrain detail and elevation, as well as key features such as trees, buildings, and other large objects. Photogrammetry allows to generate full-colour 3D and 2D models of the terrain that are easy to visualise, interpret and process. Using this data solar design teams can make accurate measurements, layout optimal arrays and carry out shading analysis.
Recent developments in technology have seen drones, rather than planes, being used to carry the equipment, making LiDAR more accessible. LiDAR uses millions of individual geo-tagged lasers returns to generate a point cloud of the area being scanned, with GPS aligned points.
Those millions of location-known laser points combine to form a 3D map. LiDAR data is often confused with a more generic dataset of ‘Point Clouds’ because it is the main output generated by LiDAR. LiDAR has many different uses and applications, including assisting autonomous vehicles, surveying power lines, coastlines and helping the Building Information Modelling sector.
LiDAR is used to create a high accuracy point cloud that can be used to produce a more accurate DTM, more than possible with photogrammetry alone. Without the photogrammetry data collected alongside it, it is only capable of that.
Photogrammetry however allows for a LiDAR point cloud to be colourised and therefore produce an Orthomosaic as well as a Digital Surface Model. This allows us to create our linework deliverable by vectorise what is visible in the imagery.
The site has areas of forest / trees plantation (arboreal vegetation) that will be removed and true ground elevation is to be captured.
The site has areas of low-density non-arboreal vegetation that will be removed and true ground elevation is to be captured.
Gullies & Streams covered by low-density vegetation where and true ground elevation is to be captured, such as width and depth.
LiDAR can provide accurate ground modelling in forested areas by penetrating the canopy layer and using advanced processing techniques to filter out vegetation and identify ground points you can produce a more accurate representant of the ground beneath.
Its accuracy may be limited by factors such as extremely dense vegetation or thick undergrowth. In such cases, fewer laser pulses reach the ground, leading to reduced accuracy. The ground reading won’t be as precise as terrain surface data from photogrammetry in bare earth areas.
Yes, pylons or wind turbines over 70m can impact data accuracy near these tall objects. Since most photogrammetry drones fly at around 120m, pilots may need to adjust flight paths to avoid obstacles, leading to missing data in those areas.
|
Area (hectares) |
Number of GCPs |
Checkpoints |
|
1-10 hectares |
7 GCPs |
2 Checkpoints |
|
10-50 hectares |
7-10 GCPs |
2-3 Checkpoints |
|
50-100 hectares |
10-15 GCPs |
3-4 Checkpoints |
|
100+ hectares |
15+ GCPs |
4+ Checkpoints |
This setup ensures sufficient accuracy and proper verification through checkpoints.
We typically use pre-made GCPs for Topographic projects, and in some cases, we use spray-painted GCPs with high-contrast paint.
Yes, we can provide Ground Surveying solutions using our trusted surveyor network. We hire licensed surveyors for most ground surveying needs upon client request.
However, it is economically advantageous for the client to map the area with a drone first, assess the data, then target Ground Surveying only to specific areas or with a more refined scope instead of deploying Ground Surveying on the complete area
Above is not a licensed surveyor, but we work with licenced surveyors for projects that require it. Our processing team also has a deep understanding of land surveying, ensuring high-quality deliverables.
The key difference between surveying and mapping lies in their purpose and precision:
Surveying is the process of measuring and determining the precise positions of points on the Earth's surface, typically for construction, land boundaries, or engineering purposes. It involves high-precision measurements and is often legally required for property delineation.
Mapping is the process of creating visual representations (maps) of areas, usually from collected data like aerial images, LiDAR, or GPS. It focuses more on spatial relationships and visualization, often used for navigation, planning, and general understanding of geography.
In short, surveying is more focused on accuracy and precision for legal and construction purposes, while mapping provides a broader visual representation of an area.
No, we do not provide the limits of administrative, communal boundaries or Cadastral Data. However, If the client has this information available, we can incorporate this data into our deliverables. Above are not responsible for the accuracy and completeness of external data.
No, it is not possible to provide accurate measurements within bodies of water using photogrammetry.
Yes, as along as the trench is clear we will be able to achieve the stated level of accuracy. However if the trench/ ditch is full of water and/or vegetation will obstruct what is possible to measure accurately using photogrammetry.
LiDAR may help further penetrate vegetation to provide a more accurate surface model and ground surveying solution may help collect more accurate data at the bottom of a ditch, allowing us to create a Digital Terrain Model.
No, however we can represent gas pipeline marker posts if visible from drone data
as wells any cadastral data provided by the client, however we cannot guarantee the accuracy of this data.
Yes, we provide True North and Grid North as well as the grid convergence angle within our DWG deliverables. Our deliverables will align to Grid North.
We don’t provide magnetic north information.
Our minimum CAD buffer for cable/ access routes is 15 meters either side of the path. This is included within the fight area which is a minimum 30 meters total corridor to allow for sufficient coverage of the area surrounding the road.