Our studio is located in Utrecht (the Netherlands) and there aren’t any particularly interesting cliffs in the next town over or even in the country. So we started looking for what actually are the closest outdoor climbing locations and settled that the Belgian Ardennes at Frëyr and Rocher du Casino were probably going to be a good balance of some proper cliffs with a wide range of difficulties, without having to travel by airplane. As you can see from the thumbnail image, Al Legne (at Frëyr) is a pretty huge cliff with the human for scale at the arrow.
Scouting
To get high quality data it is optimal to have a nice overcast day and try to avoid any moving inconsistencies between the photos. Things like leaves, animals and even people will have a major impact on your data. We chose the end of November for our trip, because there should be fewer people trying to climb and more importantly the trees don’t have any leaves anymore. Time to book a hotel and get the preparations going!
Preparing
Maybe one of the most important steps to a successful scan of a cliff is the preparations. Please do not underestimate this, we are well aware of the excitement you get from being close to the cliff and flying your drone about, but it has to be done safely!
- Be prepared to be outside for hours. So have enough warm clothes, food and (hot) drinks. It’s even a good idea to bring a tarp or a tent with some foldable chairs so you have a place to keep your things dry, out of the wind and take a rest.
- Bring enough power! Depending on the size of the cliff you need to have several battery packs for the drone and probably even have a way to recharge those packs, but also (VERY IMPORTANT) have multiple phones to control the drone with. Those phone batteries will drain really fast, especially when it’s cold outside.
- Since we are scanning climbing cliffs it’s of course also important to bring some safety gear, think about mountain shoes, ropes, carabiners, also depending on the location it might be smart to bring a helmet. And last but not least it never hurts to have a first aid kit at hand.
Scanning
Now that we are ready to go and our batteries are charged it’s time to go. Skipping some of the overhead logistics I’ll just move on to the moment we start the scanning. Based on the tests we did earlier we will use the drone to record video and use the start-stop flying to ensure we have enough frames with low blur.
We decided that it would probably be good for our source data to have multiple perspectives of the same area. To do this we fly the drone up with the camera tilted +24° and then in the same location fly the drone down with the camera tilted -45°. This would make sure that we give the photogrammetry software more information about the 3D details. After doing one vertical strip we would stop the video, move the drone a couple of meters horizontally (ensuring about 30% overlap between the strips), start a new video and then fly the new strip. When we see a particularly interesting / detailed area we would also fly some extra perspectives around it to make sure we get that data in our dataset.
After hours of flying the drone and many gigabytes of video footage later we even had some time left and decided that it would be cool to try and scan a ruin in and see if it would be good content for the game (spoiler alert: this worked great!). Now it was for sure time to head back home. In the next part we will talk about how we process these videos to get a meganormous 3D model out.
