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Surveying / Mapping / Spatial services

Builders, architects and construction companies will often need to obtain precise, survey-grade measurements of existing buildings or spaces, before construction or re-modelling efforts commence, or perhaps to verify that “as-built” construction works have been done according to the original plan. However, traditional survey methods are very time-consuming, and may not capture all the required information.

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On the other hand, drone surveys, possibly combined with ground surveys, can provide a comprehensive and precise digital “as-built” representation of an existing space or building in a very short time, with minimal disruption to on-site people and processes. If the digital representation produced has survey-grade accuracy, then precise digital measurements can then be extracted from it, at leisure.

 

Quite simply, drones can capture highly accurate and precise geo-referenced data in a number of ways, that can then be integrated into your location-based data repository (CAD, BIM, GIS, etc), as another layer of location-referenced data available to all users. This could be used, for example, by construction companies bidding for a tendered job, so they could accurately bid for the work, with a high degree of confidence in what was required, perhaps without even needing to physically visit the site!

 

Drone surveys using LiDAR scanners can provide survey-grade representations of exterior spaces, whilst hand-held LiDAR scanners provide the same result for interior spaces. And since LiDAR is an active technology, it is immune to the effects of ambient light conditions, in fact it can even be used in the dark! The LiDAR beam has multiple return paths (eg, vegetation, ground, etc), so it is also ideal for accurate terrain modelling where there is reasonably thick vegetation. It can also detect smaller, thinner objects (eg, powerlines), when compared to photogrammetric methods.

 

For exterior surfaces, drone-based photogrammetry is also an excellent tool to produce photo-realistic 3D models of the physical world, provided suitable ambient lighting is available. Drone-based photogrammetry of interior spaces may not be practical to perform, however hand-held photogrammetry can be done. Photogrammetry is the process of ortho-rectifying and “stitching together” lots and lots of overlapping photos of the area of interest, it can be used to produce;

  • Orthomap (ie geographically corrected for camera lens distortions to be truly flat)

  • 3D model (aka Digital Twin), Point Cloud, Textured Point Cloud

  • Digital Terrain Model (DTM) (ie map of the “bare earth” with no structures on it)

  • Digital Surface Model (DSM) (ie map of the “bare earth” with structures on it)

  • Vegetation Index maps (ie plant health, for agriculture)

using sensors including; visual (RGB), thermal (infrared), LiDAR, laser scanners, passive microwave (L-band), multispectral, and hyperspectral.

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Photogrammetry can be done by most basic drones using visual (RGB) cameras, however for survey-grade positional accuracy, some form of Ground Control is required. Ground Control is the way that the image output is referenced to the surface of the Earth. It can be done in one of 3 ways;

  • Using Ground Control Points that are surveyed and integrated into the processing

  • Using Real-Time Kinematics (RTK)

  • Using Post-Processed Kinematics (PPK)

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In turn, RTK can be done by either a mobile station (such as the DJI D-RTK2), a local base station, or via an external network of base stations for GPS corrections, using the internet for connection to the network. The drone itself must also have RTK functionality.

 

Using Ground Control Points only is the slowest and most cumbersome method, and may not be logistically possible in all cases. RTK is fastest / most convenient, but the mobile station method by itself may still require a small number of Ground Control Points to be used, for accuracy. RTK with an external network of base stations is very convenient, but requires the internet to be available on-site. PPK works in all scenarios where PPK data is available for that site at that time, but requires post-processing effort.

 

Since photogrammetry is derived from actual photos, it produces more realistic (but usually less detailed) 3D models than those derived from LiDAR. The equipment to produce photogrammetry is also much cheaper and more readily available, than for LiDAR scans. However, the processing of photogrammetry requires large amounts of processing power, and takes considerable time. LiDAR, on the other hand, has the advantage that most scans can be done in one pass, with results available in real-time. It also produces far smaller file sizes than that required for photogrammetry.

 

Regardless of which method you choose, the real value of this data is when it is combined with other location-referenced data, and then made available to all users and stakeholders, to form a comprehensive repository of all location-referenced data in your organisation. A Digital Twin is all this, and more. All users and all stakeholders are then working off of one single common location-based information database, thus maximising the effectiveness of the data.

 

CDS Differentiators:

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