Mavic 3M multispectral orthomosaic has streaking/checkerboard pattern

[Malalako]

I've processed multispectral images (G, R, NIR, Red-edge) captured from the Mavic 3M and everything seemed to work well until the orthomosaic stage. The orthomosaic (attached) has strange streaking/checkerboard pattern. The steps I took were:
1. Import photos
2. Change primary channel/band to NIR
3. Align photos
4. Optimise cameras
5. Build point cloud
6. Create orthomosiac (default values).

Any suggestions on what is happening here and how to correct it? The point cloud looks fine.

[Alexey Pasumansky]

Hello Malalako,

We would probably need some sample subset of images from this project that can be used to reproduce the issue on our side.

Please also specify, if you are using reflectance calibration in the project and whether the point cloud is generated based on the image data and not point cloud has been rendered to the orthomosaic.

[Malalako]

Message deleted as posted in wrong forum

[Dronisimo]

Hi Malalako,

Thanks for sharing your insights on this issue. I noticed that part of your response seems to reference support from DroneDeploy. Could you clarify if the solution you mentioned was provided by DroneDeploy or Agisoft, or if it was a combined effort? Additionally, could you provide any extra details about how you implemented the fix? I’d like to better understand the process to ensure accurate results in my own projects.

Thanks in advance for your help,

Regards,

[Malalako]

Hi Malalako,

Thanks for sharing your insights on this issue. I noticed that part of your response seems to reference support from DroneDeploy. Could you clarify if the solution you mentioned was provided by DroneDeploy or Agisoft, or if it was a combined effort? Additionally, could you provide any extra details about how you implemented the fix? I’d like to better understand the process to ensure accurate results in my own projects.

Thanks in advance for your help,

Regards,

Apologies my reply was posted in response to a different question on a different forum. I've now deletd it.

[Malalako]

Hello Malalako,

We would probably need some sample subset of images from this project that can be used to reproduce the issue on our side.

Please also specify, if you are using reflectance calibration in the project and whether the point cloud is generated based on the image data and not point cloud has been rendered to the orthomosaic.

Hi Alexey,

I can provide a subset of images - can you please clarify how these are best shared. I haven't used reflectance calibration in the project. I'm assuming you mean those reflectance panels? I couldn't afford the panels and given this was a one time flight (not part of a time series) I decided not to pursue them.

I don't understand your question about if the point cloud is based on the image data or rendered from the orthomosiac? COuld you please explain. I have outlined the steps I took on my initial post.

[Alexey Pasumansky]

Hello Malalako,

If you are using the steps like in your original post (5. Build point cloud, 6. Create orthomosiac), then you are missing generated surface  - which can be DEM or mesh, such surface should be used in "surface" field of Build Orthomosaic dialog. In your workflow you are likely using Point Cloud surface option and it means that the points are rendered to the orthomosaic.

As for the reflectance calibration, you can use Sun Sensor option in Calibrate Reflectance dialog without panel.

So I could suggest to build DEM from the point cloud, then calibrate reflectance using Sun Sensor option (images in Photos pane may get darker visually), then build Orthomosaic using DEM as a surface.

[Malalako]

Hello Malalako,

If you are using the steps like in your original post (5. Build point cloud, 6. Create orthomosiac), then you are missing generated surface  - which can be DEM or mesh, such surface should be used in "surface" field of Build Orthomosaic dialog. In your workflow you are likely using Point Cloud surface option and it means that the points are rendered to the orthomosaic.

As for the reflectance calibration, you can use Sun Sensor option in Calibrate Reflectance dialog without panel.

So I could suggest to build DEM from the point cloud, then calibrate reflectance using Sun Sensor option (images in Photos pane may get darker visually), then build Orthomosaic using DEM as a surface.

Hi Alexey,

Thank you so much. I had forgotten to do the step of creating a DEM before the orthomosaic. And hadn't worked with multispec data before so didn't realise I could use the inbuilt sun sensor to calibrate reflectance. Adding those two steps has resulted in a nice smooth orthomosaic.

Out of interest - does it matter at what stage I do the reflectance calibration? You've mentioned doing it after building the DEM but the below tutorial (for Phantom drone) suggests to do it as a first step (even before alignment stages)
https://agisoft.freshdesk.com/support/solutions/articles/31000159853-dji-phantom-4-multispectral-data-processing

[Alexey Pasumansky]

Hello Malalako,

If you need only multispectral orthomosaic as processing result, then you can calibrate reflectance any trim before building the orthomosaic. But if also point cloud colored by original bands is required, then reflectance calibration should be performed before building point cloud.

[Malalako]

Hello Malalako,

If you need only multispectral orthomosaic as processing result, then you can calibrate reflectance any trim before building the orthomosaic. But if also point cloud colored by original bands is required, then reflectance calibration should be performed before building point cloud.

Thanks for all the help