This same map area after processing through the new smoothing algorithm is shown in Figure 2 – a dramatic improvement! Our algorithm works in model space (the model on which the contours are based) and hence is guaranteed not to introduce topology errors such as contour crossings.
We have been doing a lot of experiments lately with very low cost drones and cameras (for example, the Inspire Pro) as to their suitability for volumetric mapping. The results so far are mixed. We have discovered that, when using no control (an approach often used by folks not well versed in survey grade mapping) that an error in the a priori heights fed into SfM software will result in significant scale errors. These scale errors are not immediately evident since all of the data look terrific! I hope to be publishing a report on this within the next 60 days.
We did our first flights under the new Part 107 rules. We were collecting data near an airport in Class G airspace (something we could not do under the old Section 333 waiver without a special COA). We always carefully monitor air traffic via a VHF radio. At one point we heard a pilot declare “I see a drone down there over the mine site!” This is perfectly OK under Part 107 but takes a bit to get used to!
We are concluding that if you need point clouds from imagery (dense image matching, DIM or Structure from Motion, SfM) to meet the network accuracy requirements for high grade topographic mapping (such as 1 foot contours) you are going to have to use either RTK or PPK on your flight platform. Even with fairly dense ground control, we are not seeing the accuracy levels we need without RTK/PPK (and we have tried this with different systems and cameras).
We are considering a special training session later this year on drone data workflow processing using PhotoScan/Pix4D and Topolyst. We also may work with our local flight center to combine this with a Remote Pilot certification training/testing session. Drop us a line if you are interested in this.