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In this article, I will attempt to give an overview of how we combine Drone and LiDAR survey data, via point clouds and other means. Everyone has a different method of doing this, depending on the software at their disposal, but this is the process that works best for us. Why combine the data? There are a number of reasons a project requires a combination of Drone and LiDAR point cloud data. In our case, we use a terrestrial LiDAR unit  along with aerial photogrammetry. Sometimes, the shape and height of an object means we cannot get the LiDAR device to scan the top of the target. In other cases, the area is too large to simply survey with a terrestrial LiDAR unit. An example project is a recent project to scan an old farm and it's surrounding landscape. The farm was in disrepair and needed internal and external surveying. As it was built on a glacial drumlin, the surrounding area also needed to be included. Our method was to survey the buildings with the terrestrial LiDAR scanner and then combine this with a point cloud created from an aerial survey. This point cloud would then be used as a guide to draw a detailed Autocad Revit model including the topography and buildings. Drawbacks of this method The main drawback of this method is that we are combining two datasets with differing point cloud densities. The terrestrial LiDAR survey has a point cloud density in the thousands per square meter, whereas the drone photogrammetric survey has a density of nearer the hundreds. This is not generally a problem if we understand that the two methods have different uses. It is also tough aligning two point clouds created with different hardware and algorithms. This is where accurate GNSS survey data becomes essential. [gallery size="medium" ids="7015,7014,7016"] The importance of GPS and Control Points. The importance of using accurate GPS co-ordinates and ground control points / targets cannot be understated here. If you have a wide range of effectively placed targets that are visible in both the drone survey and the LiDAR point cloud, it makes combining the two datasets immeasurably easier. There will be errors and there will be a slight difference in figures, but the more accurate you GPS control points are, the lower the error rate, ensuring the resulting combined dataset is still within accuracy limits. We use a combination…

3d Laser Tunnel survey; wet and dry Laser scanning methods have been in use for several years to survey objects, buildings and tunnels and the level of detail that can be obtained is stunning. It allows for wide range of inspections to be completed including, mapping, surface condition assessments, over and under breaking analysis, component inspection and relationship to surface features or activity. There are two approaches: a handheld laser unit or SLAM (Simultaneous Localisation And Mapping), or  terrestrial LIDAR (Light Detection And Ranging) unit; both have their advantages. A hand-held SLAM is rapid and will go places that a LiDAR unit cannot, so is preferable in long or small tunnels, but it cannot capture the detail that a LiDAR unit can, which is a slower more considered approach. Commendium will use the most appropriate method for any job and typically uses a blend of technologies to gain the desire output. With partners, The Water-Services Group, we are able to offer a multi-technological approach to surveying tunnels, aqueducts or aquifers. Uniquely, with software built in-house, we are able to combine and synchronise SLAM, LiDAR, Ground Penetration, Sonar and Airborne survey data into complete 3D models of underground subjects, so that, for instance, we can create a geolocated map of a tunnel, accurately assess the depth below ground of a tunnel at any point on the surface, accurately measure spatial relationships between underground features and give a detailed, even forensic, 3D condition survey, a full 3d laser tunnel survey all in dry and partially or fully flooded systems. We can survey where humans cannot venture using robotic vehicles, but also have the necessary confined space, access, and safety training to physically venture into these tunnels. We have recently been testing these combined technologies in Speedwell caverns in Derbyshire. Here a stairway leads to a boat ride along 450m of half-flooded tunnel, meticulously mined out in the 1770s, to a large chamber. We where able to combine sonar data from underwater, SLAM data long the tunnel and high quality LiDAR data in the chamber at the end, into a single 3D dataset.