Aerial photogrammetry and its associated products (orthophotoplans, DTM, 3D composition, contour lines, etc.) are now very old techniques. Aerial photography’s origins date back to the time of hot air balloons and its real growth in importance came during World War 1. Until recently it was a costly exercise, since it required the use of expensive camera equipment mounted on board an aeroplane or helicopter; its use was reserved for mapping large territories.
Current techniques allow orthophotoplans to be produced at minimal cost with images captured from a drone or ultra-lights.
Two examples of work undertaken:
- Production of an orthophotoplan and DEM for the landscaping of a property in the Normandy countryside.
- Orthophotoplans of a farm and a village in Africa.
- NDVI - NDRE maps
Production of an orthophotoplan and DEM for the landscaping of a property in the Normandy countryside.
This magnificent plot of wooded land, in the middle of which sits a dwelling in pure Norman style, needed certain landscaping to be undertaken. So that this would be in keeping with the surroundings, we were asked to produce an orthophotoplan, and to determine the height of neighbouring trees.
We undertook the work using a multi-copter drone flying at a height of 50m, to obtain images of 2.5cm resolution at ground level. To georeference everything in the national geodetic system (Lambert 93 and NGF [general levelling of France] altitudes), we positioned targets which we surveyed with a Trimble GeoXR GPS, receiving differential corrections from the Teria network.
Data Elevation Model (DEM)
Using the same images, we were able to create a data elevation model (DEM).
By knowing the altitude of each point, it is possible to measure the height of the trees (25 metres for those located in the South West corner).
With a different configuration, and using the same techniques, we would have been able to determine the isotopes of a lake to be landscaped - generating the contour lines and calculating the volume of earth to be moved.
In association with partners equipped with light aircraft or microlights, we can produce orthophoto maps for areas which are too small for traditional photogrammetry and too large for the use of a drone.
The following image was created during acceptance tests on our production chain.
The Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Red Edge index (NDRE) are graphical indicators that can be used to analyze vegetation. They are computed using combination of green, red and near-infrared bands of a photo produced with a multispectral camera.
The images below show the same place with representation in RGB (standard Red Green Blue colors) and NDVI. We have used a SenseFly Ebee UAV with a RGB sony camera for the left map and a MultiSPEC 4C camera for the right map.