49 lines
2.3 KiB
Markdown
49 lines
2.3 KiB
Markdown
---
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title: Raspberry Pi pan-tilt mount for huge images, part 2
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author: Chris Hodapp
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date: October 4, 2016
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tags: photography, electronics, raspberrypi
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---
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In my [last post](./2016-09-25-pi-pan-tilt-1.html) I introduced some
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of the project I've been working on. Those of you who thought a
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little further on this might have seen that I made an apparatus that
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captures a series of images from fairly precise positions, and then
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completely discards that position information, hands the images off to
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[Hugin][] and [PanoTools][], and has them crunch numbers for awhile to
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derive *the very same position information* for each image.
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That's a slight oversimplification - they also derive lens parameters,
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they derive other position parameters that I ignore, and the position
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information will deviate because:
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- Stepper motors can stall, and these steppers may have some
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hysteresis in the gears.
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- My pan and tilt axes aren't perfectly perpendicular.
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- The camera might have a slight tilt or roll to it.
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- The camera's [entrance pupil][] may not lie exactly at the center of
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the two axes, which will cause rotations to also produce shifts in
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position that they must account for. (More on this will follow
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later. Those shifts in position can also cause parallaxing, which
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is much more annoying to account for.
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[No, it's not the nodal point. No, it's not the principal point.][npp])
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That is, the position information we have is at best a guess; it's not
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sufficient on its own. However, these tools still do a big numerical
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optimization, and a starting position that is "close" can help them
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along, so we may as well use the information.
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- We're using Panotools and our apparatus together; they can
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cross-check each other.
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- Our position info also turns readily into a .pto file which Hugin
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can visualize.
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[ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/
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[forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138
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[raspistill]: https://www.raspberrypi.org/documentation/raspbian/applications/camera.md
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[25mm-lens]: https://www.amazon.com/gp/product/B00N3ZPTE6
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[Hugin]: http://wiki.panotools.org/Hugin
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[PanoTools]: http://wiki.panotools.org/Main_Page
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[entrance pupil]: https://en.wikipedia.org/wiki/Entrance_pupil
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[npp]: http://www.janrik.net/PanoPostings/NoParallaxPoint/TheoryOfTheNoParallaxPoint.pdf
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