UAV's for Topographical Survey Drawings
(written whilst working for Plowman Craven)
Yesterday we completed our first UAV flying job since I moved to Plowman Craven. This was a topographical survey of a development in Purfleet, East London. The area is the first section for us to be instructed on of a much larger topographical survey in this area.
The 15 Ha site included a mixture of land types including scrub land, a 1km long foreshore and a couple of inaccessible piers. The main problem with surveying this using conventional techniques was that the foreshore was tidal, and so could only be surveyed during a 2 hour window. Additionally there was a 20 foot drop onto the foreshore behind the flood wall which made it incredibly unsafe and difficult to get access to.
Author: James Dunthorne
Published: 12 August 2016
Ground control was installed strategically across the site to ensure an accurate model could be generated. Most of these control points were sprayed onto solid surfaces using a stencil and biodegradable spray paint. Some total station work was also required to pick out some points on the piers to control those areas during the processing stages. In total it took just 4 flights to collect the data which equated to just 40 minutes flight time. These flights were centred around the low tide which was at noon to ensure that as much of the shoreline was revealed. Just over 650 overlapping images were taken in total, with around 20 control points being surveyed.
The next steps involve processing this into a 3D model using photogrammetry software. The point cloud will get passed across to our BIM team who use the data to extract the 3D CAD drawings. If there is any detail that cannot be extracted effectively from the UAV data, then another day on site may be required by one of our land surveyors to pick this up and add it into the CAD drawings. Finally the survey is quality controlled against other survey data to guarantee the level of accuracy our clients expect.
After speaking to one of our land surveyors, they estimated that it would have taken them around 7 days to complete this survey using traditional techniques, and would have been extremely dangerous to survey the foreshore.
Even if another trip is required by a land surveyor to pick up extra detail, using a UAV has not only reduced the time taken to complete this survey from 7 days to less than 2, it has also saved our land surveyors from having to work in dangerous locations. Additionally, we will now be able to provide an up-to-date aerial photo-mosaic of the site to our client to help them plan work, conduct briefings and complete health and safety assessments during the next phases of their work. A great result all around, which just shows the benefits UAVs are bringing our industry.