Agisoft Metashape

Agisoft Metashape => Camera Calibration => Topic started by: mfran2002 on September 09, 2016, 08:51:35 PM

Title: Lens to calibrate Sequoia
Post by: mfran2002 on September 09, 2016, 08:51:35 PM
Hello,
I'm trying to calibrate my Sequoia using Lens but, during the calibration procedure, I receive log messages like the following :

Code: [Select]
Calibrating lens...
corners hessian: 4.022 non-maxima: 0.041 correspondencies: 0.217 refine: 1.666
At least 3 photos with properly detected corners are required, calibration skipped
corners hessian: 4.091 non-maxima: 0.04 correspondencies: 0.168 refine: 1.619
At least 3 photos with properly detected corners are required, calibration skipped
corners hessian: 4.687 non-maxima: 0.045 correspondencies: 0.201 refine: 1.8
At least 3 photos with properly detected corners are required, calibration skipped

What it means? What is wrong?

Thanks a lot for your help
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 02:44:09 PM
Hello mfran2002,

Can you post an examples of the images, that you are using for the calibration?
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 10, 2016, 03:33:03 PM
each photo is more than 512KB may I send you an email?
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 03:35:38 PM
Hello mfran2002,

You can send them to support@agisoft.com with .lnz project file.

Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 03:49:15 PM
Thank you for sending the files.

First of all I should say that you cannot calibrate in the same group the images that have different pixel resolution or different focal length, and calibration by the single image only is not possible.
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 10, 2016, 03:58:00 PM
mmmm..... I understand

my problem is that during the shoots I cannot see the frame.
I go blinded :-/ and it is very difficult

I try to stay at the same distance during the shoots, and I try not to take the perimeter/edges

but it is not so simple
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 10, 2016, 04:12:50 PM
have you some suggestion for correctly taking photos?

my procedure into LENS is very simple:

1. add photos
2. tools -> calibrate

is it correct?
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 04:19:25 PM
Hello mfran2002,

Yes, the procedure is correct, but I don't understand why the images have different resolution, are they cropped automatically?

Also the images do not look sharp enough.
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 10, 2016, 04:41:55 PM
due to the fact that I didn't see what I was framing I had to crop the images, and I cropped them manually

this is also (maybe) the reason why they have different resolution

because I had to stay close to avoid taking the edges, the pictures are not so sharp (I guess)
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 04:54:09 PM
Hello mfran2002,

If you crop the images, it is no longer possible to say, for example, where the principle point of the original image is located. So cropping is very highly not recommended both for Lens and PhotoScan.
If there's anything else apart from the checkerboard by the image borders, that's not a problem.
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 10, 2016, 05:37:03 PM
great!

someone told me that it was essential to have only the board, recommending not to frame the edges.
And since I can not always take the photo without frame the edges I thought to cut them.

The distance of the photos from the board should always be the same (more or less), right?
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 05:41:25 PM
If could be slightly different, just try to make photos under different angles.

But I still doubt if the calibration would give you results more accurate, than autocalibration in PhotoScan, since when performing calibration in Lens you need to keep the same settings, that will be used in the actual projects, like focusing on infinity, for example, but with this approach the calibration images will be very blurred.
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 10, 2016, 05:51:36 PM
sorry Alexey, รน
I didn't understand your last consideration, may you please explain me again?

and another doubt: what is "autocalibration in PhotoScan"? How can I do it?

sorry again, limit of mine...  :-\
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 10, 2016, 05:53:41 PM
When the images are aligned in PhotoScan, it automatically estimates the parameters of the internal calibration, so it may be more accurate, than calibration performed in the laboratory conditions that are much different from the real shooting process.
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 11, 2016, 11:54:24 AM
sorry but then for what should I have to use LENS?

I thougth it must be used for calibration of the cameras...

if not, for what else?
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 12, 2016, 10:12:29 PM
Hello Alexey,
I have tried anyway to generate xml calibrating files from Lens.

May I send to you the shoots (together with lnz, xml and log files) so you can tell me if it is all ok or not?

thanks a lot!

PS: via wetransfer as usual...  :D
Title: Re: Lens to calibrate Sequoia
Post by: Alexey Pasumansky on September 14, 2016, 11:21:36 AM
Hello mfran2002,

Looks better, but when I've said that it is acceptable to have some background in the image frame, I meant just a small areas by the border, the checkerboard pattern should occupy the most of the image frame area.
Title: Re: Lens to calibrate Sequoia
Post by: mfran2002 on September 19, 2016, 04:06:57 PM
You are right Alexey,
but it is very difficult to frame correctly without monitoring what you are framing...
There is no display or some other way to check what the camera is framing...

I will try to repeat my shoots and then I will send you again for your check

thanks!