At DroneDeploy, we define a good map to have:
- 99%+ coverage of the area of interest
- High data quality
- Fast delivery
But on occasion we will not be able to achieve this, and you may see holes (unstitched regions) in the map. This could be caused by several factors (expanded on below). Stitching can be considered to be a black box process; data is input, but the mathematical process driving the stitching is complex and difficult to predict - or even to precisely understand. In that sense, you could think of it as an art.
There are various causes of stitching failures:
- Motion Blur
- Unfocused cameras
- Vignetting on images
- Insufficient image overlap
- Non-nadir photos (e.g. photos taken during turns)
- Photos taken at a low altitude
- Homogenous imagery (e.g. full crop cover in fields)
It is useful to understand the map stitching process to help optimize your chance of generating successful maps. In short, each photo taken from the drone contains ‘features’ such as crop rows, trees, buildings, trails left by equipment, or anything that is distinctly recognizable in the visual space.
As the aircraft takes continuous photos during the mission, it captures multiple photos of each distinct feature, from multiple angles. These features are identified and matched by a mathematical process, and aligned on top of each other. This is not simple. Consider making a puzzle, where all the pieces had straight edges, all the pieces overlapped by an unknown amount, and there was a different perspective in each image that meant the pieces had to be warped by an unknown amount to make them match. Now include the fact that vertical structures will look different from each side!
This would be impossible for a human.
How to improve your Map Quality
We have listed some of the factors that govern the coverage of these maps. If your map was of poor quality, here are a few simple things you can do to improve it. You can adjust the flight settings by clicking on the left hand sidebar of the app to open your flight's settings:
Note that you can also change settings from the desktop under the "Advanced" tab.
Flying higher gives the camera lens (with a given field of view) more land area to cover in a single image. This grants the drone more chances to cover common unique features in multiple images, which can help mapping in areas with homogeneous imagery (such as tree canopies or agricultural areas). It also enables higher frontlap to be achieved for a given camera. Flying higher is the single most powerful way to improve data quality.
Modifying flight path
Using the Flight Direction feature allows you to change the direction that your drone flies. Changing the flight path can assist when you are mapping a narrow shape so that the drone conserves battery life. It can also assist in flying in and out of the wind. As you modify your flight's rotation, go back to your flight plan to review the changes to ensure it works best for your flight. Be sure to review where your flight is starting so that the path you are making is clear.
Fly on an overcast day
Flying when the sky is overcast allows you use the clouds as a giant light diffuser. Light diffusers are common in professional photography because they provide soft, even lighting on your subject. This can greatly reduce shadows, blurriness, and glare from reflective surfaces all of which will improve the quality of your map. This technique is most effective for 3D models and should not be used during sunrise and sunset as this can discolor your images.
By clicking on "Advanced" in your flight's settings, you can gain even greater control of the plan.
Increasing side overlap (sidelap) during planning
Flying with more overlap between each leg of the flight is the easiest way to get more matched features in the imagery, but it does come at the expense of reducing the area that your drone can cover in one flight.
Increasing front overlap (frontlap) during planning
This will increase the number of photos taken during each leg by simply making your camera take photos more quickly. Your camera will have a hard limit on how fast it can operate, so after you hit that point you will not see any further improvements.
If you'd like to start your flight from a certain waypoint or are continuing a mission, select the waypoint you would like the drone to start its mapping from.
Max Flight Speed
You can set the maximum speed at which the drone can fly. Please note, the maximum speed does not denote the drone's actual speed. The drone's flight speed can vary depending on your flight parameters, such as the altitude and overlap settings.
Check your camera settings and quality of individual photos
DroneDeploy does attempt to make your camera capture imagery at its absolute best quality. However, ultimately image quality is governed by so many other parameters (some of them listed above), that it is useful for users to check the quality of the individual photos captured as the drone is performing the mission flight. You can toggle the camera settings on to adjust your exposure and focus manually in the DJI Go App.
Examples of Good Stitching
Below are example of two consecutive photos captured during a flight over a canyon where you can see common features. This is ideal for stitching.
Examples of Common Issues
There are a few common issues that cause low quality maps. Learn how to recognize and prevent these issues here:
This is caused by fast-moving drones or vibration - this either means the shutter speed isn't fast enough, or that you are flying too fast. The best way to solve this is to improve shutter speed, but flying slower or higher will help as well. Here is an example of what motion blur looks like:
If your images look like this, it may be due to an unfocused camera. If you are using a DJI drone, you can look here for information on how to turn off the default DJI camera settings. Make sure that autofocus is on, and that there are no dust or particles on the lens. You can adjust the camera settings manually from the DJI GO app.
Vignetting is caused by a lack of light. Re-flying the mission with less cloud cover can help with this. Check the lens for dust or particles that may be causing the dark images.
Insufficient image overlap
The higher the image overlap, the easier it is for our software to process your image. High overlap gives you greater map detail over a smaller total space.
By including the horizon, the internal distance of the map will be distorted. The software will try to include the areas far away in stitching rather than the area of interest immediately below.
Photos taken at low altitude
Taking photos at a low altitude lowers the surface area per image, which will make them difficult to stitch together. This can result in blurry maps. It is difficult to cover as much ground in one flight as you could from a higher altitude.
Make sure to always obey your local/national altitude restriction regulations.
A great example of homogenous imagery is a field with full crop cover. Because there is little variation or distinguishable features, and a tendency to have hard-to-determine patterns, it can be difficult to stitch together the images. The same attributes can apply to fields with full crop cover as well.
The anomaly of homogeneous imagery affects all image processing software. It’s just that difficult for computers to process.