Messages

1

Camera Calibration / MicaSense calibration irregularities

« on: June 16, 2023, 03:44:29 AM »

Hello,
We have been processing MicaSense MX Dual imagery and are getting inconsistent results. Some of our panels are unreliable, because we work in forests where shadows are hard to avoid. Depending on the flight, the best ortho may be produced by a single panel + sun sensor, multiple panels + sun sensor, or sun sensor only. However, the results sometimes do not change between one panel and multiple panels. i would like to know more about how MetaShape chooses which values to use.

I have two questions:
(1) What is the calibration method used when only "sun sensor" is checked? There is a dark level value stored in the XMP data, but what is used to determine the upper limit in order to produce reflectance values?

(2) When multiple reflectance panels are used, how does MetaShape determine which model to fit? In other words, does it average the panel values? Or fit a best line across time? The Micasense website says: "The date/time of the panel images can be used to define a time-varying model. This time-dependent model can then be applied to each image individually, taking into account the image's own date/time stamp. This can be achieved with a simple linear interpolation across CRP captures, or with a more complex least-squares fit model depending on the accuracy needed." Which one is used?

Thank you very much!

2

General / Filter dense cloud process

« on: May 15, 2021, 09:57:23 PM »

Hi Alexey,
I am very curious to know how the filter dense cloud process works.
Is it a decimation?
Are points randomly dropped/kept or are their locations and values averaged?
I would like to use this tool as part of scientific research, so I would need to know how the points are produced.
Thank you very much!

3

Python and Java API / Re: Crop dense cloud by shape

« on: January 19, 2021, 08:53:15 AM »

I would also love to know how to implement this feature in the API!

4

General / Valid matches marked as invalid

« on: March 09, 2020, 09:14:28 AM »

Hi Alexey,
For one of my sites, Metashape in unable to align almost half of the photos (437/721 aligned). The images are of good quality and resolution, and the software is finding many CORRECT matches between them, but marking them as invalid anyway! This happens at high and low accuracy settings...

Several other people have asked how the program decides whether a match is valid and I have not seen an answer yet. What is going on?

Thanks,
Sam

5

General / Filter dense cloud values

« on: March 06, 2020, 10:46:27 PM »

Hi Alexey,
I am wondering how exactly the "filter dense cloud" function works.
The points that it produces do not appear to be the same as in the full dense cloud. So I am assuming that it is voxelizing rather than sub-sampling. Is this correct?
Are the resulting reflectance values simply averages of all pixels within each voxel?
How about the XYZ coordinates? Are they averaged too?
If so, each pixel potentially represents a spectral signal from several cameras, no?
Thank you very much!

6

General / Re: Reflectance/Radiometric Calibration on MicaSense Sequoia

« on: August 23, 2018, 11:39:04 PM »

Hello All, It was (and still is) unclear to me how the different combinations of the check-boxes in the 'Calibrate Reflectance' dialog influence NDVI results of the resulting orthos. Therefore, I conducted a comparison of NDVI values from 3 separate projects for the following combinations of the check-boxes:

1) 'Use Sun Sensor' Checked
2) 'Use Reflectance Panels' Checked
3) 'Use Sun Sensor' and Use Reflectance Panels' both checked.


As noted by other users my images and resulting orthos were very washed out when I calibrated using options 2 and 3. The NDVI values for these were similar, but nonsensical (basically shadowed areas were the only pixels that contained positive NDVI values). I've attached my results displayed as a classification of NDVI with a range of -1.0-0.35 for dead vegetation (red) and 0.35-1.0 for live vegetation (green). Also included is the average NDVI value for each project. I used the same calibration panel images and photoscan workflow settings to process the three projects. I'm using a reflectance panel from MicaSense, a CSV containing reflectance values provided from MicaSense, and a Parrot Sequoia.

Is it recommended to use both check-boxes when you have calibration panel imagery collected for your project both pre and post-flight?

What do these settings actually do to the exif data?

How can you tell if your calibration was successful (right now I just notice the washed out imagery and the sensitivity values changing in the 'camera calibration' dialog)? I notice it normally takes 1-2 seconds for photoscan to perform the calibration.

Thanks

Hello all,

I would like to echo these questions.

I am processing imagery from the MicaSense RedEdge with the goal of obtaining point clouds with reflectance values for each band attached. The program automatically detects the calibration panels just fine but when "use reflectance panels" is checked, the images appear very dark, and the resulting NDVI values are extreme. Using only the sun sensor gives much more plausible results.

I have attached histograms of my NDVI values with (first) and without (second) calibration.

And, it would be useful to have the option of normalized reflectance values.

Thanks!