Fen Pumping Station
Objective and outcome of the task
These missions were to further refine mission planning and aircraft & camera settings. They were also to fly over a residential house sized building sufficiently separated from an urban or suburban environment to develop operational capability and safety also applicable to urban and suburban environments.
The mapping missions were flown as planned and without any technical or operational issues, giving confidence for performing similar missions in more urban environments. The 2D maps presented below show some variation in the broad characteristics such as vegetation & feature colours when zoomed out, but most of the differences are only visible when zoomed in. Using the ortho mission result as the reference the three oblique missions captured greater detail due to the greater number of photos captured and the oblique nature of the photography also enabled 3D models to be created rather than just a 2D map. The first smart oblique mission (mission 3) captured 20% more photos than the plain oblique mission (mission 2) with no noticeable improvement in 2D map and 3D model quality. But the second smart oblique mission (mission 4, over a reduced area of interest) required 70% less photos than the first smart oblique mission (mission 3) with no reduction of the 2D map and 3D model quality.
The missions took substantially different elapsed times and numbers of photos. Mission 1 (ortho) took 5 minutes to cover 12,100 sqm (1.21 hectares/3.1 acres) capturing 166 photos. Mission 2 (oblique) took 10 minutes to cover 10,700 sqm (1.1 hectares/2.6 acres) capturing 435 photos. Mission 3 (smart oblique #1) took under 9 minutes to cover 7,300 sqm (0.7 hectares/1.8 acres) capturing 520 photos. Mission 4 (smart oblique #2) took under 4 minutes to cover 1,600 sqm (1.1 hectares/2.6 acres) capturing 158 photos. The final mission (mission 4) was by a significant margin the most efficient in terms of output quality vs. flying time, area covered, and number of photos captured.
How the data was gathered and processed
Four missions were flown over the fen drainage pumping station to test the effect of DJI mission type (ortho, oblique, smart oblique & smart oblique over a small area) on the time & distance flown, number of photos, and the quality of photographs, 2D map and 3D model.
Mission 1 (ortho)
Mission 2 (oblique)
This mission comprises five parts, where a standard ortho sub-mission is first flown over the top, and the following four parts are flown in each cardinal direction extending beyond the subject area to gather oblique photos capturing detail in the third dimension of the site's structures. This type of mission is required to generate a 2D map and a 3D model.
Mission 3 (smart oblique)
This mission is broken into two parts, where the two parts are flown over the subject area and extend away from the subject area in both directions. The two parts are flown perpendicular to each other and can comprise multiple parallel passes to adequately cover the subject area. This mission is required to generate a 2D map and a 3D model.
Mission 4 (smart oblique, reduced area)
This was mission based on the previous mission but with the subject area reduced to be closer to the building walls, to understand the effect of the subject area boundary on photo and map/model quality.
The missions took approx. 5, 10, 9 & 4 minutes elapsed flying time respectively, and 166, 435, 520 & 158 photos (respectively) were captured during the four passes over the site. The photos were processed using the DJI Terra app, taking just over 19, 53, 57 & 9 (respectively) minutes of processing time on a Windows 11 PC with a 32-core Intel Core i9-14900 processor, 64GB of RAM and an Asus Nvidia 4060 GPU.
2D Map
The 2D map was output by DJI Terra app as a GeoTIFF file. The GeoTIFF was used to create PDF and JPG files of the 2D ortho-mosaic and uploaded into Google Earth Pro to create a geo-referenced tile overlay on the Google Earth globe. This can help visualise the subject in its surroundings.
The GeoTIFF is also a very detailed ortho-mosaic image and can be examined to understand the condition of the subject, e.g. damage to woodwork, masonry, brickwork, roof tiles/panels, etc.
Standard DJI ortho mission
Standard DJI oblique mission
Standard DJI smart oblique mission
Standard DJI smart oblique mission, reduced area
3D model animation
The 3D model can be examined to enable measurements of distance, area, volume and slope to be taken; these have been verified to be within millimetres of the actual values.
The 3D model was shared as a link from the DJI Modify app, to be viewed in a web browser. Animation of the model in the viewer was screen recorded. (The viewer can navigate around the model using the mouse. The 3D model can also be output to a number of formats compatible with various CAD, GIS, etc. apps.)
Live 3D model animation
A live version of the Pumping Station 3D model is available here. The model can be navigated to examine details of the property.
To rotate the model, press and hold the left mouse button; to translate the model, press and hold the left mouse button and a shift key; and to zoom the model in & out, use the mouse scroll wheel.
This is a reduced fidelity (but still 100s MB) version of the 3D model, but it will still take 15-20 seconds to load and initially only a white screen with a set of x, y & z axes will be shown. When the model loads the view starts below the model, so to bring the building into view click the left mouse button and drag down a few centimetres.
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