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General / Re: Do I need to calibrate cameras?
« on: March 31, 2016, 08:01:48 PM »
You are welcome, avp:
Given that your small cameras have fixed optics, I guess you can rely on self-calibration if object and cameras setup geometry are aproppriate.
But once is asumed you can consider your cameras are true fixed-lens cameras, why do you reject to calibrate them with an optimal object/scene?
Even though two camera modules might look identical, they should be considered as diferent cameras and therefore, each corresponding output image sets should be grouped in the calibration dialog.
To calibrate easily, take series of convergent photos of an object with lots of texture (a granite stone wall might work great) at similar working distance you will use with your piles. Create an independent chunk for each camera module and store your calibration parameters for future use once you are satisfied with the cameras alignment.
Light sources should not influence calibration unless the key points are strongly linked to shadows borders and the light sources are in movement during photo scanning. This may lead to bad structure estimation thus may make self-calibration biased.
You can trust a regular dslr with a fixed lens (fine legacy glasses are the best choice in my opinion) if focus ring is taped or locked by any means. I myself have drilled my voightlander focus ring in three points and locking headless bolts have been added. The entire lens mount has been glued to the body side with epoxi and I don't plan to detach this lens any more unless it becomes absolutely necesary. Some cheap lens adaptors are not recommended, as they are usually machined with lower specs and the lens mount can shift sideways quite a lot.
It might sound exagerated, but, please, apply some force from side to side to your lens near the mount and will probably notice it shifts at least some tenths of mm. Lets say 0.2mm. For a usual pixel size of five microns, this means principal point is shifting about 40 pixels which is not a negligible amount. If you detach your lens, you won't be capable to mount it again in the very exact same place, and that's why I glued mine.
Best
Given that your small cameras have fixed optics, I guess you can rely on self-calibration if object and cameras setup geometry are aproppriate.
But once is asumed you can consider your cameras are true fixed-lens cameras, why do you reject to calibrate them with an optimal object/scene?
Even though two camera modules might look identical, they should be considered as diferent cameras and therefore, each corresponding output image sets should be grouped in the calibration dialog.
To calibrate easily, take series of convergent photos of an object with lots of texture (a granite stone wall might work great) at similar working distance you will use with your piles. Create an independent chunk for each camera module and store your calibration parameters for future use once you are satisfied with the cameras alignment.
Light sources should not influence calibration unless the key points are strongly linked to shadows borders and the light sources are in movement during photo scanning. This may lead to bad structure estimation thus may make self-calibration biased.
You can trust a regular dslr with a fixed lens (fine legacy glasses are the best choice in my opinion) if focus ring is taped or locked by any means. I myself have drilled my voightlander focus ring in three points and locking headless bolts have been added. The entire lens mount has been glued to the body side with epoxi and I don't plan to detach this lens any more unless it becomes absolutely necesary. Some cheap lens adaptors are not recommended, as they are usually machined with lower specs and the lens mount can shift sideways quite a lot.
It might sound exagerated, but, please, apply some force from side to side to your lens near the mount and will probably notice it shifts at least some tenths of mm. Lets say 0.2mm. For a usual pixel size of five microns, this means principal point is shifting about 40 pixels which is not a negligible amount. If you detach your lens, you won't be capable to mount it again in the very exact same place, and that's why I glued mine.
Best
...I should have read more carefully but original subject should have been related to targets not to markers ID. Sorry, Alexey.