This article explains how to properly set the DJI Mavic 3 Multispectral (DJI Mavic 3M, DJI M3M) before flying and how to process the images in PIX4Dfields.
Introduction
The DJI Mavic 3 Multispectral is equipped with a 20-megapixel RGB camera and a 5-megapixel, 4-band multispectral camera. Additionally, it features an RTK antenna for enhanced precision.
Flight settings recommendations
- Depending on the task, capture both RGB and multispectral imagery or capture only one type of image. The RGB camera produces .jpg images while the Multispectral camera produces .tiff images. For each capture, one RGB and four multispectral images will be generated.
- Ensure that Dewarping is turned off before capturing RGB images.
- When Dewarping is disabled, the images will display a black vignette in the corners:
This is expected and perfectly fine. The distortions are removed by PIX4Dfields during the processing.
- When Dewarping is disabled, the images will display a black vignette in the corners:
- If Dewarping is left on during image capture, it may cause the resulting maps to be shifted by several meters, compromising both relative and absolute accuracy.
- Avoid using the "Elevation optimization" feature, as it will cause the drone to capture non-nadir images toward the end of the flight.
- This can adversely affect the processing quality of the data.
- This can adversely affect the processing quality of the data.
- The flight height directly influences the resolution, Ground Sampling Distance (GSD), of the images. Below is a table and a visual comparison illustrating how different flight heights impact the GSD, Flight Time and Speed.
* Flying with similar settings may not yield the exact values shown above. These values are estimates and might not be entirely precise.
What Reflectance panel should I use?
- The multispectral camera is not fully radiometrically calibrated, as the manufacturer only does a relative calibration. All bands are calibrated against the standard NIR band. Therefore, the camera will not provide reflectance factors but only relative values proportional to reflectance.
- A reflectance target is required to obtain reflectance factors. Only Micasense and Sentera targets are compatible with the Mavic 3 Multispectral.
- Without such a target, only self-normalizing indices produce meaningful results, i.e. indices that don't depend on the absolute value. Examples of such indices are NDVI, NDRE, VARI, SIPI2, LCI, BNDVI, and GNDVI. Not self-normalizing are TGI and MCARI.
How to process the M3M in PIX4Dfields
When processing in PIX4Dfields, each camera has to be processed separately. If both images are imported, a message will pop up to choose one.