it_team4_FOREst 2 September 2017For many years, biomass in the form of wood chips has been increasingly used to generate energy from renewable raw materials. Accurate volume determination of the delivered biomass quantities is a fundamental necessity for planning for planning, logistics and inventory. However, the determination of the exact volume used to be a challenge.
In his bachelor thesis, Nikolas Katz, in 2017, developed a methods to determine bulk materials – here wood chips – by using UAVs.
Determination of volume through the analysis of UAV images
The measurement and volume calculation of hollow and solid forms (such as bulk material/chippings heaps) by means of stereophotogrammetry based on the basis of close-range aerial images, collected with unmanned aerial vehicles (UAV) was demonstrated in a Nikolas Katz’s thesis.
According to the thesis’s the calculation of the volume of a 3D object is basically divided into four steps:
- creation of an automatic flight plan and virtual aerial map with at least 80 % image overlap in both flight directions
- creation of images of the object under investigation from different angles;
- processing of the images to 3D point clouds with “structure for motion” algorithms;
- volume computation from the point cloud.
The method presented in the bachelor theis for calculating the volume of larger bulk material heaps is based on a photogram-metric method using UAV close-up aerial images. The inner and outer orientation values of the RGB aerial mosaics are calculated directly with the help of a 3D image vector by linking homologous pixels in each image. The actual measurement of the 3D-objects or volumes is contactless and can be carried out within a very short period of time without any major technical effort on the basis of the following parameters of a systematic and automatic drone flight on site.
The thesis compared the measurements on the 1 m3 cube and a 1,700 m3 wood chip cluster. The research yielded similarly results: the error of volume determination in the cube was about 1 % and only slightly higher in the test measurements on the large cluster (Fig. 6) with only 1.3 %. Comparative measurements at the reference cluster (Figs. 2 and 3) also showed very low error values with deviations between 1 to 3 % from the real total volume. Overall, this represents a significant improvement in accuracy compared to conventional measurement methods.
Get more details in AFZ-DerWald 22/2017: “Hackschnitzelhaufen mit Drohnentechnik vermessen” (in German only)