In my previous article I highlighted the importance of ground control for aerial drone surveying. You really can’t provide a GIS ready product unless it is coordinated by ground control. Or can you? Now I am not going to start advocating not using ground control but what if you can’t acquire ground control for your given area of interest. Are there other options?? Well yes there are. They are not as accurate as supplying surveyed ground control but they will provide a product which can be used in your system if you just need to view a mosaiced image.
1) Deploy a drone with built in Real Time kinematics (RTK). For example the Ebee Plus or Robota Eclipse RTK. These drones communicate with a base station and corrects it’s horizontal and vertical coordinates based on the base station known location and communication with the GPS satellite systems. Removing the GPS wander we see in uncorrected GPS data. Each photo centre then provides a more accurate position, so that when post processing products perform the image mosaicing the final product is a lot better geometrically than without ground control.
2) No RTK drone? Well Esri’s Drone2Map provides “use map tool” to supply ground control. What does this mean? Well most people know that ArcGIS provides basemaps. Street maps, aerial imagery etc. but what a lot of people don’t know is that ArcGIS also provides a world elevation surface. Drone2Map consumes both the world imagery and world elevation service. When you use the “Use map tool” and select a visible location on the map, it reads the X,Y,Z from the elevation surface and supplies this as the ground control. Remember though that the world elevation service is a generalised elevation surface, so in areas of high variability this will be smoothed somewhat. But at least you have some control on the output products, so they will be in relatively the right location.
Now if you combine both the RTK product and the Drone2Map surface coordinates then you are going to get a better output product as well.
Finally, it is always important to remember that when people look at imagery or maps they assume it to be correct. How many people have driven down a closed road because their navigation tool said it was open. So always when you deliver the products, supply the accuracy metadata, so that the end user understands the accuracy of the product they are looking at and don’t use it for purposes it shouldn’t be.