When you first start to plan mapping missions with UAVs, you realize there are a lot of factors at play. How high should I fly? What speed should my UAV be flying? How much front overlap and sidelap do I need? What should my camera settings be? What camera lens is best? These are all questions that UAV pilots ponder when they first start mapping with drones. This is especially true if you have a custom built drone that can accept multiple cameras or sensors.
The following post outlines some tips that will lead to better UAV data, many of which I discovered after learning the hard way. There is nothing worse than having to refly a mission to get the results you needed!
Tip #1 – While flying low gives you better resolution, flying higher can avoid many potential headaches.
It’s important to strike a balance here, as flying higher can save you a lot of time during post-processing, plus allow you to cover more area with fewer flights. Get a good grasp on what your client’s end use of the drone data is. Is maximum resolution really necessary to help with their decision making or to solve their problem? To cover the most ground possible on a given mapping mission, I often find myself flying our maximum allowable altitude here in Canada (120 m), knowing that the imagery is still at a much higher resolution than it would be coming out of a manned aircraft system (traditional air photo collection) or satellite.
By flying higher, you can also maintain a high sidelap percentage (e.g. 75%) while still covering a large area on a single flight. Don’t underestimate the benefits of planning one or two flights instead of five or six. When you have many different flights that you are stitching together, there is a lot more room for error in your final product.
Tip #2 – Set the bar high on accuracy, and record Ground Control Points.
If you are mapping with drones for projects, you should consider yourself as an operator in the world of professional surveying (even if this might seem like a stretch at first). With any survey product, data accuracy should be at the top of the priority list, and establishing Ground Control Points (GCPs) is one way to assist with that. While mapping without ground control may still provide your end user with some added value, it also limits the usefulness of the derivative products, such as contours (terrain data). Many projects, particularly government contracts, also have minimum data standards to abide by, and GCPs will assist in meeting them.
Other benefits of GCPs can be realized when you are stitching data from multiple flight missions together. When you have established ground control in the overlapping regions of two flight plans, it makes it easier to tie the two mosaics together and can even help to remove distortions in the final processing. For most clients, recording GCPs should not be done with your phone or a recreational GPS… consider making the investment in an industry-grade GPS if you are serious about UAV mapping.
Tip #3 – Process your own data, and take full control.
In an attempt to minimize costs and effort, there is a common user trend in UAV mapping: to allow a 3rd party to process your data, either directly through an app or through a separate upload service. In my experience, there are several downsides to this approach. The first relates to transparency. The processing of your drone data should not happen in a black box, even if the results appear to be great coming out the other side. When you invest in your own photogrammetry software (e.g. Pix4D Mapper), you have full control over every step, and you stay in tune with the source of any potential errors.
Another big downside to automated processing is the lack of options to enter and establish GCPs. This continues to be a major issue with the majority of these processing apps… you can’t include your Ground Control Points, which are often critical to the accuracy and ultimate success of your project. Lastly, you are dependent on others to deliver specific data products. Often times you’ll need to output custom datasets. For example, you may want to generate new contours at a different interval, imagery in a different map projection or datum, or a point cloud at a different density. Processing yourself allows you all of this flexibility.
Tip #4 – If you don’t have background knowledge in photogrammetry, GIS or surveying, consult with someone who does. You’ll get more out of your drone data.
If you are just starting to map with drones, this tip may seem like I’m trying to overcomplicate things. Maybe you have an easy-to-use drone and are just looking for a basic map of your site, so you can get away with not having any expertise in photogrammetry, GIS or surveying. While that may be the case, over time you’ll begin to understand the usefulness of working with these subject matter experts. UAVs are just another tool used to accomplish something they’ve been doing for decades.
Whether it’s capturing and analyzing aerial imagery, creating terrain models, classifying the earth’s surface, or modelling the environment – this is old news to people in our respective industries. Drones are just a new way of performing a familiar task at a higher resolution, as an alternative to manned aircraft and satellite data collection, for example. The value of this expertise also shines when problems arise, when custom solutions are necessary, or during the data delivery phase when your drone data needs to be combined with an existing survey or analyzed in a GIS.
Tip #5 – Know your camera and the conditions you’re operating in.
With so many new UAV solutions out there, it’s easy to get caught up in the unmanned aircraft themselves, and not focus on the camera. As I’ve mentioned in other posts, you should pay special attention to the camera you are using, as it’s capturing your data and providing all of the value to your end user. Even some mainstream UAVs with proprietary camera systems allow you to have full manual control of your camera settings. Take advantage of this rather than settling for “Auto” options. Applying shutter priority and optimal ISO settings (to fit the lighting conditions) can drastically reduce the number of blurry images that your drone takes during its mapping mission. If you’re new to mapping with UAVs or you’ve recently added a new camera to your setup, it’s wise to test various settings and get to know your camera well before committing to a new client project.
If you aren’t doing it already, start to think like a photographer. This means paying attention to small details, like the sun position in relation to where you are shooting your subject, and taking note of where shadows may develop and ruin your shots. If you are mapping, the time of day that you’re planning flights is also important. If you have the flexibility, fly as close to solar noon as possible to minimize shadows in your final imagery. Excessive shadows can cause problems with stitching your images together, and can also wreak havoc on analysis that you may perform on the imagery.
In future posts, I will present even more specifics on how to get the most out of your drone mapping missions. In the meantime, I hope you can use some of these tips to impress your next client… feel free to pose questions in the comments below. Good luck out there!
Mike Morellato is the lead author and founder of WorkingWithDrones.com. He works with drones and their data at Strategic in Campbell River, BC (Canada).