Added assets_external placeholder; more updates to 2016-10-04 draft

assets_external/readme.txt

@@ -0,0 +1,6 @@
+This directory is something of a placeholder for larger assets than
+should be committed into git along with everything else.  It might
+eventually be absorbed into something like git-lfs, or it might move
+to some other format.
+
+For now: Don't commit things here into git, just sync them manually.

posts/2016-10-04-pi-pan-tilt-2.md

@@ -11,11 +11,11 @@ little further on this might have 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
-derive *the very same position information* for each image.
+calculate *the very same position information* for each image.
 
-That's a slight oversimplification - they also derive lens parameters,
-they derive other position parameters that I ignore, and the position
-information will deviate because:
+That's a slight oversimplification - they also calculate lens
+parameters, they calculate other position parameters that I ignore,
+and the position information will deviate because:
 
 - Stepper motors can stall, and these steppers may have some
   hysteresis in the gears.
@@ -35,15 +35,14 @@ help them along, so we may as well use the information.
 
 Also, these optimizations depend on having enough good data to average
 out to a good answer.  Said data comes from matches between features
-in overlapping images (say, using something like [SIFT][] and
-[RANSAC][]).  Even if we've left plenty of overlap in the images we've
-shot, some parts of scenes can simply lack features (like corners)
-that work well for this.  We may end up with images for which
-optimization can't really improve the estimated position, and here a
-guess based on where we think the stepper motors were is much better
-than nothing.
-
-(TODO: Stick a photo here to explain features?  Link to my CV text?)
+in overlapping images, say, using something like [SIFT][] and
+[RANSAC][].  Even if we've left plenty of overlap in the images we've
+shot, some parts of scenes can simply lack features like corners that
+work well for this (see chapter 4 of
+[Computer Vision: Algorithms and Applications][szeliski] if you're
+really curious).  We may end up with images for which optimization
+can't really improve the estimated position, and here a guess based on
+where we think the stepper motors were is much better than nothing.
 
 If we look at the [PTO file format][pto] (which Hugin & PanoTools
 use), it has pitch, yaw, and roll for each image.  Pitch and yaw are
@@ -60,18 +59,61 @@ grid in which I shot images.  The only real conversion needed is to
 convert steps to degrees, which for these steppers means using 360 /
 64 / 63.63895 = about 0.0884, according to [this][steps].
 
-With no refining, tweaking, or optimization, here is how this looks in
-Hugin:
+With no refining, tweaking, or optimization, only the per-image
+stepper motor positions and my guess at the lens's FOV, here is how
+this looks in Hugin's fast preview:
 
-(supply screenshot here)
+[![Hive13](../images/2016-10-04-pi-pan-tilt-2/hugin-steppers-only.jpg){width=100%}](../images/2016-10-04-pi-pan-tilt-2/hugin-steppers-only.jpg)
+
+*(This is a test run that I did inside of [Hive13][], by the way.  I
+used the CS-mount [ArduCam][] and its included lens.  Shots were in a
+14 x 4 grid and about 15 degrees apart.  People and objects were
+moving around inside the space at the time, which may account for some
+weirdness...)*
+
+Though it certainly has gaps and seams, it's surprisingly coherent.
+The curved-lines distortion in Hugin's GUI on the right is due to the
+[projection][], and perfect optics and perfect positioning information
+can't correct it.  Do you recall learning in school that it's
+impossible to put the globe of the world into a flat two-dimensional
+map without distortion?  This is exactly the same problem - which is
+likely why Hugin's GUI shows all the pictures mapped onto a globe on
+the left.  That's another topic completely though...
+
+Of course, Hugin pretty much automates the process of finding control
+points, matching them, and then finding optimal positions for each
+image, so that is what I did next.  We can also look at these
+positions directly in Hugin's GUI.  The image below contains two
+screenshots - on the left, the image positions from the stepper
+motors, and on the right, the optimized positions that Hugin
+calculated:
+
+[![Hugin comparison](../assets_external/2016-10-04-pi-pan-tilt-2/hugin-comparison.png){width=100%}](../assets_external/2016-10-04-pi-pan-tilt-2/hugin-comparison.png)
+
+They sort of match up, though pitch deviates a bit.  I believe that's
+because I shifted the pitch of the entire thing to straighten it out
+(or perhaps it did this automatically to center it), but I haven't
+examined this in detail yet.
+
+A full-resolution JPEG of the result (after automated stitching,
+exposure fusion, lens correction, and so on), is linked below:
+
+[![Hive13 full](../assets_external/2016-10-04-pi-pan-tilt-2/hive13-20161004-fused-smaller.jpg){width=100%}](../assets_external/2016-10-04-pi-pan-tilt-2/hive13-20161004-fused.jpg)
+
+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
+prettiest photo or the most technically-perfect one (it's full of lens
+flare, chromatic aberration, overexposure, noise, and the occasional
+stitching artifact).
+
+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
+sensor.
 
 TODO:
 
-- We're using Panotools and our apparatus together; they can
-  cross-check each other.
-- Conversion for steppers; axes that Hugin/Panotools use and what I
-  use
-- dcraw conversion?
+- This was done completely with a raw workflow, blah blah blah
+- How did I wire the steppers, vs. how does Hugin see things?
 
 [ArduCam]: http://www.arducam.com/camera-modules/raspberrypi-camera/
 [forum-raw-images]: https://www.raspberrypi.org/forums/viewtopic.php?p=357138
@@ -84,4 +126,7 @@ TODO:
 [steps]: https://arduino-info.wikispaces.com/SmallSteppers?responseToken=04cbc07820c67b78b09c414cd09efa23f
 [SIFT]: https://en.wikipedia.org/wiki/Scale-invariant_feature_transform
 [RANSAC]: https://en.wikipedia.org/wiki/RANSAC
+[hive13]: http://hive13.org/
+[projection]: http://wiki.panotools.org/Projections
+[szeliski]: http://szeliski.org/Book/
 [pto]: ???

site.hs

@@ -35,6 +35,10 @@ main = hakyll $ do
     match "assets/**" $ do
         route   idRoute
         compile copyFileCompiler
+        
+    match "assets_external/**" $ do
+        route   idRoute
+        compile copyFileCompiler
 
     match "images/favicons/*" $ do
         route $ customRoute $ takeFileName . toFilePath