What is the difference between LiDAR and photogrammetry?
Generally speaking, LiDAR is better in areas of high vegetation and during low-light environments, while drone photogrammetry is better for creating highly-visual digital assets.
LiDAR works by sending pulses of light to the earth's surface or a feature on it and measuring the time it takes to reflect back.
Photogrammetry is the art of capturing high-resolution photographs to recreate a survey area.
For more information, read our LiDAR vs photogrammetry comparison.
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What are point clouds and how do I use them?
A point cloud is the representation of a geographical area, terrain, building or feature which is compiled through a huge collection of points and plotted in 3D space.
Each point has its own set of Cartesian coordinates (X, Y, Z) and each virtual georeferenced point represents its real-world equivalent, such as a section of wall, ground or road etc.
Point clouds can be used to measure an object's depth, elevation, shape and exact geolocation.
They can also contain colour values, such as RGB and intensity.
For more information, read our guide to point clouds.
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What is ground sample distance?
Ground Sample Distance (GSD) is the distance between the centre of two adjacent pixels measured on the ground. It is a measure of accuracy in aerial mapping and remote sensing operations.
Learn how to calculate GSD and find out more about why GSD is important for drone surveying on the blog.
What are ground control points?
Ground control points – or GCPs as they are known – are marked points on the ground that have a known geographic location.
For aerial survey applications, GCPs are typically required as they can enhance the positioning and accuracy of the mapping outputs.
This method can be laborious – as it requires laying out and precisely geolocating numerous control points - and can take a large amount of preparation.
Using RTK and PPK correctional technologies can minimise or even eliminate the need for GCPs. Drones such as the DJI Phantom 4 RTK and M300 RTK benefit from this technology.
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PPK Vs RTK: What is the difference?
RTK is a GPS correction-technology technique that provides real-time corrections to location data when the survey drone is capturing photos of a site. Real-time correction is a major industry advantage.
PPK is another GPS correction-technology technique that works to correct location data, except in the cloud after the drone data has been captured and uploaded.
In other words, this means that in terms of positional correcting, RTK does this during the flight, while PPK makes the changes afterwards.
RTK has many benefits, such as the pinpoint accuracy of the aircraft during flight, and accurate geotagging of the information the aircraft captures.
However, RTK requires a very specific base station and other pieces of equipment that work together in order to process data in real-time. Signals can also be obstructed which results in loss of correction data. This is not an issue with PPK.
PPK also removes the requirement for GCPs saving you further time in the field.
When it comes to drone surveying, is it best to use RTK and some ground control points?
Yes. Possibly the best combination is deploying a drone with RTK and a small number of strategically-positioned ground control points.
Having flown the DJI Phantom 4 RTK, Terra Drone Europe believes that in some cases the accuracy that can be achieved without any GCPs is less than 3-4cm, but when in need of greater accuracy, it is advisable to use a number of ground control points - but it is still a reduction compared to traditional surveying methods.
The breakdown below provides an overview of surveying with and without RTK and how GCPs can help.
GCPs Alone
High Accuracy
High Speed
Low Cost
Drone Without RTK
Low Accuracy
High Speed
Low Cost
Drone With RTK
High Accuracy
High Speed
Low Cost
RTK + GCPs
Highest Accuracy
Medium to High Speed
Low Cost
What’s the difference between DEMs, DTMs and DSMs?
Digital Elevation Models (DEMs) are a visual representation of the elevation data for every point captured on your site.
Instead of depicting how your site actually appears in person, DEMs generally use colour to indicate differences in elevation.
DEMs are a superset of both Digital Terrain Models (DTM) and Digital Surface Models (DSM).
So what is the difference between a DTM and DSM?
DTM: A bare-earth surface model. In other words, featuring purely the terrain and ground.
DSM: The most general form of surface model that includes all acquired points, representing natural and man-made features. A DSM includes the tops of buildings, trees, powerlines and other objects. In essence, it is a canopy model, and only sees the ground when nothing else is above it.
For more information, read our DEMs vs DTMs vs DSMs comparison guide.
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What are digital twins?
Digital twins are digital representations of a physical asset.
Like the real world they represent, digital twins are ever-changing; continuously adjusting to reflect the near real-time status or condition of the real-world asset.
As a synchronised and dynamic dataset, digital twins can be used to gain valuable insights and more fully understand the physical asset.
These continuous updates are fed from a rich tapestry of technology, including sensors, drones, reality capture, GIS and BIM integration, real-time Internet of Things, cloud computing, advanced AI and machine learning.
Digital twins provide a single view that can be accessed throughout the entire lifecycle of a project and can be used to represent current, past, or even future states of assets.
For more information, read our guide to digital twins.
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What is SLAM surveying and why should I use it?
SLAM stands for Simultaneous Localisation and Mapping. It is an innovative method of on-the-go mapping, building a map and providing locational data simultaneously.
Other benefits of SLAM include: It does not require GPS; it is mobile; it is versatile - use it underground, inside, outside and from the sky.
SLAM can be used for a range of applications, such as AEC, real estate, conservation, and public safety.
Read our guide to SLAM surveying for more information.
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What is the difference between multi-band and single-band RTK GNSS receivers?
There are a number of differences between multi-band and single-band RTK GNSS receivers.
Primarily, single-band receivers can only obtain one frequency band from satellites, whereas multi-band receivers work with several frequency bands.
This has a knock on affect to the performance capabilities of each type of receiver. For instance, multi-band receivers can achieve a fixed position quicker and have a longer baseline (distance between base and rover).
Typically, multi-band receivers are more expensive than single-band receivers.
For an in-depth comparison, read our multi-band vs single-band blog.
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Ecosystem
