Top Twelve Mission Planning Tips for Getting the Best Possible Orthomosaics
IGIS Tech Notes describe workflows and techniques for using geospatial science and technologies in research and extension. They are works in progress - we welcome feedback in the comments below!
Top Ten Twelve Mission Planning Tips for Getting the Best Possible Orthomosaics
- Plan your missions so a minimum amount of time lapses between flights over adjacent areas, to minimize the difference in sun angles and shadows. If you have to fly on different days, try to fly adjacent areas around the same time of the day.
- Plan the stop and start points of your flight lines to minimize the amount of time between adjacent areas. Let one flight start where the previous one ended.
- If you can’t avoid dissimilar illumination between adjacent areas, fly the edge dividing the two areas on both flights, so the stitching software has more data to work with when color matching. Process the images from two flights together, if possible.
- Fly high. Flying higher has many advantages - less blur, larger image footprints, fewer lens distortion effects, and fewer images to process. Unless you really need very fine resolution, err on the side of flying higher (e.g, 300ft). You can use a GSD calculator to estimate what the final pixel size will be.
- Fly close to solar noon - because shadows move slower at the peak of the day. This particularly applies to long flight lines.
- If you have a fixed camera (i.e., not mounted on a gimble), try to fly in line with the wind (to reduce the amount of canter).
- Also try to fly in line with the sun angle (to reduce the amount of bidirectional reflectance distribution function).
- If you can't fly with the wind and also the sun angle, pick the lesser of two evils. Flying crosswind will cause less canter if the wind speed is not that high. BRDF is less of an issue around solar noon, especially during the summer when the sun is highest in the sky, but more of an issue in landscapes with hills or regularly spaced features (like row crops or orchards).
- If possible avoid flying when there are cloud shadows in the study area, particularly if there are high winds and the shadows are moving quickly. Overcast clouds are less of an issue if the light is diffuse and even.
- Fly 70% overlap (forward and back and side-to-side) for flat terrain, and more for hilly topography (but never more than 90%).
- Avoid launching in the footprint of your flight — unless you want to be one of the features in your orthomosaic!
- Use manual white balance instead of auto white balance. White balance determines the color tint of each image. Auto white balance sets the white balance based upon the proportion of greens, browns, dark, etc. it sees in the image. This usually works fine for an individual image but can be dramatically different over a set of images from a single flight (see below). You often set the white balance in the camera’s manufacturer’s app (e.g., DJI Go, Solo, GoPro Capture), then close the app and run switch to your Mission Planning app.