Site in West London
The brief: To produce a 3d ground terrain model of the site to enable future volume calculations. The site was in an interesting location, close to the M4, a railway line and a river.
Methodology: Our in-house drone/uav was to be used to map the site using photogrammetry, this is a quick and accurate way of surveying the site. Before setting foot on site, risk and pre-flight assessments were carried out in accordance with our operations manual, on the day Heathrow Flight Control was contacted to gain permission to fly within their controlled area.
On site, a recce was performed to check over the site, establish landing and take-off areas and assess suitable Ground Control Point locations, these ground controls points were then established and marked using a series of nails and pegs, these were painted to enable visibility from the sky. These ground control points were then located using a GeoMax GPS receiver, transformation to OSGB36 was calculated in real-time.
3 separate flights were performed to gain plenty of overlap but also at different heights and angles to enable accurate calculation of the terrain. The majority of the flights were flown at a height of 50 metres to generate a resolution of 1.20cm/px, due to the unevenness of the terrain this was more than ample. Total flight time 50 minutes, number of images 754.
Processing: The GPS coordinates were extracted direct from the GPS receiver as a CSV file, this was then imported straight into the photogrammetry software, the images were then aligned and GCPs matched to the relevant images. Once aligned a point cloud was produced, then a 3d mesh and finally a high resolution ortho-rectified image. This data was then passed onto the client for the final volume comparisons.
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