Phantom 4 Multispectral

[sakaic]

Hi all,

Just got delivery of the Phantom 4 Multispectral. Would anyone here be interested in a sample dataset? I am uploading it to my Google Drive so if anyone wants it let me know and I will share a link here.

Does anyone have one yet? Any recommended workflow?

[Paulo]

Please do,

it would be very interesting to test

[Alexey Pasumansky]

Hello sakaic,

It would be helpful, if you can share the dataset acquired with the multispectral sensors, we'll check, if anything should be developed on our side to support that.

[ArchArch]

I would be interested too, thank you. I teach GIS and Remote Sensing (for archaeology) and would love to play around with the data. Cheers!

[sakaic]

Hi Guys,

You can download it here

https://drive.google.com/drive/folders/1FbQgvme0aisRcknUrhB4u3hbgY8fWn2x?usp=sharing

It stitches fine but I guess at the moment reflectance calibration is not possible yet.

Let me if there are problems downloading. My responses will be slow as I am in the field with a mapping mission.

Cheers

[Alexey Pasumansky]

Hello sakaic,

Thank you for sharing the dataset.

We'll study the available information related to sun sensor meta-data and at some point will add the support for it and proper reflectance calibration operation.

In the current dataset it seems that sun sensor relative rotation and sun sensor absolute orientation angles are not available in the meta information.

[sakaic]

Hi Alexey,

Is it possible to use the FlightRollDegree, FlightPitchDegree and FlightYawDegree data in the XMP data since the sunshine sensor is bolted directly on the RTK antenna?

[Landy]

Hello Alexey,
Do you know if support has been added for the Phantom 4 pro multispectral yet?  Our uni has just purchased one and was I keen to give some data a go in metashape.
cheers
Bill

[smhese]

We would also like to know if support for the P4M reflectance calculation with a reference panel photo is possible soon. So far the results are totally screwed when a Micasense panel (50%) is used.  Uncalibrated processing to a dense point cloud and orthomosaic works however fine. But without the calibration option the idea of using the P4M for research purpose investigating plant properties is useless. Manual raw correction with the 50% panel might work. But Pix4D supports radiometric correction of P4M data as far as I can see!

Kind regards! Sören Hese (Friedrich-Schiller-University Jena/Germany)

[Alexey Pasumansky]

If you are observing any problems with the reflectance calibration operation, it would be helpful, if you could send the minimal dataset for testing to support@agisoft.com. So that we could check on our side, if there's anything wrong with our implemetation.

[DoubleJ]

Sometimes the calibration panel works well but other times not so much. For me, it mostly impacts some blue band captures.

One big issue is that the P4M has a different definition of vignette correction in comparison to Micasense so DJI is discussing this and trying to find the best way to solve the issue.

Given the vignette issue, I suspect that some other metadata values may not have a one-to-one correspondence with MicaSense metadata. Also, given that vignette correction is not successful, and it is part of the calibration panel routine, the calibration panel would need to be in the center of the frame so it isn't in a dark spot in the image. I'm not sure if anything else in the calibration routine "breaks" due to the vignette issue. The vignette can be solved with "calibrate colors" later on in processing, but the DJI metadata parameters might need to be translated to MicaSense equivalent, or the Agisoft code might need to be modified for the P4M.

Also, for troubleshooting this, I recommend against trying to use the sun sensor and just stick to panel calibration.

[nprokofyev]

I didn't try P4M for myself, but our customers are also interested whether it's possible to use Micasense panel for P4M calibration.

It seems unclear to me what can go wrong. It is supposed to be just a reflectance target...

Whithin the Rededge calibration model, which AFAIK is implemented in Metashape, there are two possible sources of differences between P4M and RedEdge: V(x,y) or a1 ( see https://support.micasense.com/hc/en-us/articles/115000351194-RedEdge-Camera-Radiometric-Calibration-Model )

I am not sure, but suppose a1 is a band multiplier (listed in metadata) which is supposed to represent integral band transmittance (Can't be wrong).
V(x,y) is a vignette correction function. Does P4M provide vignette corrections? Even if isn't, V(x,y) turns to 1 and the rest part of the formula may still work.

I'd apreciate any updates on the topic

[eddison]

Hello, nice to greet you, a P4 Multispectral Drone has just been purchased.

The images can be calibrated radiometrically and recognizes the metadata of the multispectral phantom 4 light sensor in Metashape?

thank you

Eddison

[uarsteam]

Sometimes the calibration panel works well but other times not so much. For me, it mostly impacts some blue band captures.

One big issue is that the P4M has a different definition of vignette correction in comparison to Micasense so DJI is discussing this and trying to find the best way to solve the issue.

Given the vignette issue, I suspect that some other metadata values may not have a one-to-one correspondence with MicaSense metadata. Also, given that vignette correction is not successful, and it is part of the calibration panel routine, the calibration panel would need to be in the center of the frame so it isn't in a dark spot in the image. I'm not sure if anything else in the calibration routine "breaks" due to the vignette issue. The vignette can be solved with "calibrate colors" later on in processing, but the DJI metadata parameters might need to be translated to MicaSense equivalent, or the Agisoft code might need to be modified for the P4M.

Also, for troubleshooting this, I recommend against trying to use the sun sensor and just stick to panel calibration.

DoubleJ,

Any update on DJI's deliberation over the vignette definition issue? I recently started working with the P4M data in a big way and noticed an awful "brightness" or "hotspot" effect in roughly the center of low-altitude images. It's especially noticeable in the NIR band images, resulting in images where vegetation reflectance appears completely saturated in the center of the image but fades as you move away from the center. Is this to what you are referring about DJI's "discussions", or is it some other phenomenon?

Best,

UARSteam

[bravemaster3]

Sometimes the calibration panel works well but other times not so much. For me, it mostly impacts some blue band captures.

One big issue is that the P4M has a different definition of vignette correction in comparison to Micasense so DJI is discussing this and trying to find the best way to solve the issue.

Given the vignette issue, I suspect that some other metadata values may not have a one-to-one correspondence with MicaSense metadata. Also, given that vignette correction is not successful, and it is part of the calibration panel routine, the calibration panel would need to be in the center of the frame so it isn't in a dark spot in the image. I'm not sure if anything else in the calibration routine "breaks" due to the vignette issue. The vignette can be solved with "calibrate colors" later on in processing, but the DJI metadata parameters might need to be translated to MicaSense equivalent, or the Agisoft code might need to be modified for the P4M.
Also, for troubleshooting this, I recommend against trying to use the sun sensor and just stick to panel calibration.

I think the sun sensor correction is still not doing a good job (when you don't have homogeneous conditions, i.e. if you have some images with sun and others with dark clouds on a cloudy day, you get some bright and dark spots in the final orthomosaic). I wanted to avoid that by not using the sun sensor, but the blue band alone had issues when the other bands looked good. The issue with the blue band was that there are strips of different values... but generally the reflectance values are a lot lower (e.g. 0.005 vs. 0.3 for instance) than the other bands, which is not usually the case in my experience with my sites.
Please note that what you see in the attachment (strips) is just in the blue band,which reflects in the true color composite attached. Here I only used reflectance panels.
The second attachment is the orthomosaic when I use the sun sensor for calibrating reflectance.

EDIT!!
What I said about the blue band only is not true. This is because I did not create a mask for all bands but only for the blue bland for the panel reflectance correction... Now, the same happens to all the bands instead. So, that is normal because probably there was sun light during those parts of the flight.

However, the bright spots on the sun + reflectance correction is still a problem....
Thanks,