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A few more links on Pi pan tilt part 2

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Chris Hodapp 2016-10-05 16:39:05 -04:00
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posts/2016-10-04-pi-pan-tilt-2.md
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@ -6,12 +6,16 @@ tags: photography, electronics, raspberrypi
--- ---
In my [last post](./2016-09-25-pi-pan-tilt-1.html) I introduced some In my [last post](./2016-09-25-pi-pan-tilt-1.html) I introduced some
of the project I've been working on. Those of you who thought a of the project I've been working on. This post is a little more
little further on this might have seen that I made an apparatus that technical; if you don't care, and just want to see a 91 megapixel
captures a series of images from fairly precise positions, and then image from inside [Hive13][], skip to the end.
completely discards that position information, hands the images off to
[Hugin][] and [PanoTools][], and has them crunch numbers for awhile to Those of you who thought a little further on the first post might have
calculate *the very same position information* for each image. seen that I made an apparatus that captures a series of images from
fairly precise positions, and then completely discards that position
information, hands the images off to [Hugin][] and [PanoTools][], and
has them crunch numbers for awhile to calculate *the very same
position information* for each image.
That's a slight oversimplification - they also calculate lens That's a slight oversimplification - they also calculate lens
parameters, they calculate other position parameters that I ignore, parameters, they calculate other position parameters that I ignore,
@ -19,14 +23,19 @@ and the position information will deviate because:
- Stepper motors can stall, and these steppers may have some - Stepper motors can stall, and these steppers may have some
hysteresis in the gears. hysteresis in the gears.
- My pan and tilt axes aren't perfectly perpendicular. - The pan and tilt axes aren't perfectly perpendicular.
- The camera might have a slight tilt or roll to it. - The camera might have a slight tilt or roll to it due to being built
that way, due to the sensor being mounted that way, or due to the
whole assembly being mounted that way.
- The camera's [entrance pupil][] may not lie exactly at the center of - The camera's [entrance pupil][] may not lie exactly at the center of
the two axes, which will cause rotations to also produce shifts in the two axes, which will cause rotations to also produce shifts in
position that they must account for. (More on this will follow position that they must account for.
later. Those shifts in position can also cause parallaxing, which ([No, it's not the nodal point. No, it's not the principal point.][npp]
is much more annoying to account for. More on this will follow later. Those shifts in position can also
[No, it's not the nodal point. No, it's not the principal point.][npp]) cause parallaxing, which is much more annoying to account for. To
get what I mean, close one eye and look at a stationary item in the
foreground, and then try to rotate your head without the background
moving behind it.)
That is, the position information we have is subject to inaccuracies, That is, the position information we have is subject to inaccuracies,
and is not sufficient on its own. However, these tools still do a big and is not sufficient on its own. However, these tools still do a big
@ -53,13 +62,13 @@ angle of view too, but as with other parameters it's okay to just
guess and let the optimization fine-tune it. The nominal focal length guess and let the optimization fine-tune it. The nominal focal length
probably won't be exact anyhow. probably won't be exact anyhow.
Helpfully, PanoTools provides tools like `pto_gen` and `pto_var`, and Helpfully, PanoTools provides tools like [pto_gen][] and [pto_var][],
I use these in my script to generate a basic .pto file from the 2D and I use these in my script to generate a basic `.pto` file from the
grid in which I shot images. All that's needed is to add up the steps 2D grid in which I shot images. All that's needed is to add up the
taken to reach each shot, convert steps to degrees, which for these steps taken to reach each shot, convert steps to degrees, which for
steppers means using 360 / 64 / 63.63895 = about 0.0884 (according to these steppers means using 360 / 64 / 63.63895 = about 0.0884
[this][steps]), and making sure that the positive and negative degrees (according to [this][steps]), and making sure that the positive and
correspond to the right direction in each axis. negative degrees correspond to the right direction in each axis.
With no refining, tweaking, or optimization, only the per-image With no refining, tweaking, or optimization, only the per-image
stepper motor positions and my guess at the lens's FOV, here is how stepper motor positions and my guess at the lens's FOV, here is how
@ -105,13 +114,16 @@ exposure fusion, lens correction, and so on), is linked below:
It's 91 megapixels. The full TIFF image is 250 MB, so understandably, It's 91 megapixels. The full TIFF image is 250 MB, so understandably,
I didn't feel like hosting it, particularly when it's not the I didn't feel like hosting it, particularly when it's not the
prettiest photo or the most technically-perfect one (it's full of lens prettiest photo or the most technically-perfect one (it's full of lens
flare, chromatic aberration, overexposure, noise, and the occasional flare, chromatic aberration, overexposure, sensor noise, and the
stitching artifact). occasional stitching artifact).
However, you can look up close and see how well the details came However, you can look up close and see how well the details came
through - which I find pretty impressive for cheap optics and a cheap through - which I find quite impressive for cheap optics and a cheap
sensor. sensor.
Further posts will follow on some other details, and hopefully other
images!
[ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/ [ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/
[forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138 [forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138
[raspistill]: https://www.raspberrypi.org/documentation/raspbian/applications/camera.md [raspistill]: https://www.raspberrypi.org/documentation/raspbian/applications/camera.md
@ -127,3 +139,5 @@ sensor.
[projection]: http://wiki.panotools.org/Projections [projection]: http://wiki.panotools.org/Projections
[szeliski]: http://szeliski.org/Book/ [szeliski]: http://szeliski.org/Book/
[pto]: http://hugin.sourceforge.net/docs/manual/PTOptimizer.html [pto]: http://hugin.sourceforge.net/docs/manual/PTOptimizer.html
[pto_gen]: http://wiki.panotools.org/Pto_gen
[pto_var]: http://wiki.panotools.org/Pto_var