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content/sundries/a-very-digital-artifact/index.md

@@ -6,4 +6,87 @@ date = "2022-11-11"
 tags = ["3dprinting", "CAD", "GIS", "CNC", "art", "sundries", "proclamation"]
 +++
 
-![a CNC-carved exaggerated relief of California made of plywood](PXL_20220723_214758454.jpg)
+![A plywood slab carved with CNC into a topographic representation of California][main_image]
+
+# A birthday wish
+
+Last summer, I wanted to get my wife something nice for her birthday. For many years, she had
+expressed an occasional and casual desire for a topographic carving of the state of California,
+where we live, and I thought it might be something I could figure out how to get her. In the end,
+after many dozens of hours of work, five weeks, and several hundred dollars paid to a professional
+CNC machine shop, I had the artifact shown in the picture above. This is the story of its creation.
+
+# First steps
+
+Before you ask, I did not do a ton of research before embarking on this. As I write this, about six
+months later, it only now occurred to me to do a basic search for an actual physical thing I could
+buy, and luckily it seems that CNC-carved wooden relief maps of the whole state are not trivially
+easy to come by, so, *phew!*
+
+No, my first step was to see if there were any shops in the area that could carve something out of
+nice plywood, about a week before the intended recipient's birthday. I found one that was less than
+ten minutes away, and filled out their web contact form. They had a field for material, and I said,
+"some nice plywood between 0.75 and 1.0 inches thick or similar" (I didn't know exactly what was
+available and wanted to give broad acceptable parameters), and under "project description", I wrote,
+
+>  A relief map of California, carved from wood. Height exaggerated enough
+to visibly discern the Santa Monica mountains. I can provide an STL file if needed.
+
+For some [incorrect] reason that I only later examined, I just sort of assumed that the shop would
+have a library of shapes available for instantiating into whatever material medium you might
+need. But just in case, I included that hedge about being able to provide an STL file. Needless to
+say, that was a bluff.
+
+![the programmer's creed: we do these things not because they are easy, but because we thought they
+were going to be easy -- from twitter user @unoservix, 2016-08-05][programmers_creed]
+*<center><sup><sub>me, every time</sub></sup></center>*
+
+Also needless to say, my bluff was called almost immediately, and I had the following exchange with the
+shop:
+
+> *CNC Shop*: STL can work but I can’t manipulate it, which could save some money. If possible can it
+>be exported to an .igs or .iges or .stp format?
+>
+> *Me*: Yeah, STP should be no problem. Can you give a rough estimate of the cost for 1x2-foot relief carving?
+>
+> *Shop*: Without seeing the drawings, I can’t give even a close price but in the past they range from
+>a few hundred dollars to several thousand dollars.
+>
+> *Me*: That's totally fair! I'll get you some files in a few days.
+
+As you can see, I leaned even harder into the bluff; my next communication with the shop was nearly
+four weeks later. But that's getting ahead of things.
+
+# Meshes and solid bodies
+
+First off, let's talk about file formats and how to represent shapes with a
+computer.[^math-computers] I said I could provide an *STL
+file*. [STL](https://en.wikipedia.org/wiki/STL_(file_format)) is a pretty bare-bones format that
+describes the outside surface of a shape as a set of many, many triangles, each of which is described
+by three 3D points. This format is popular with 3D printers, which is how I became familiar with
+it.
+
+This type of representation is easy to create and read, but it's not great for manipulation.
+
+# Public data
+
+## From space?
+
+## Thanks, California state!
+
+## In Australia, it's pronounced "g'dal"
+
+## Give it a good smear
+
+# Test prints
+
+# Final cut
+
+# Thanks
+
+[main_image]: PXL_20220723_214758454.jpg "A plywood slab carved with CNC into a topographic representation of California"
+
+[programmers_creed]: programmers_creed.jpg "jfk overlaid with the programmer's creed: we do these things not because they are easy, but because we thought they were going to be easy"
+
+[^math-computers]: I'm pretty sure this is more "represent shapes with math" than with a computer, but
+the computer is just helping us do the math and it's more relatable.

content/sundries/a-very-digital-artifact/notes.txt

@@ -0,0 +1,143 @@
+inital comms with CNC shop:
+------------------------------
+Me: "project description": A relief map of California, carved from wood. Height exaggerated enough
+to visibly discern the Santa Monica mountains. I can provide an STL file if needed.
+
+Shop: STL can work but I can’t manipulate it, which could save some money. If possible can it be
+exported to an .igs or .iges or .stp format?
+
+Me: Yeah, STP should be no problem. Can you give a rough estimate of the cost for 1x2-foot relief carving?
+
+Shop: Without seeing the drawings, I can’t give even a close price but in the past they range from a
+few hundred dollars to several thousand dollars.
+
+Me: That's totally fair! I'll get you some files in a few days.
+------------------------------
+
+next comms with shop three weeks later:
+------------------------------
+
+Hi Steve, I'm sorry for taking so long to get back to you! I had a harder time producing the IGES
+file than I thought I would, but I think this should be OK:
+
+(snip url to file)
+
+It's 51 megabytes, otherwise I'd attach here.
+
+As modeled, there's probably more high-frequency detail in the mountains than is necessary, as I'm
+going for something that feels nice to the touch so smoother is better. It's also modeled at a
+slightly larger scale than necessary, though not too far off (it's 500x577mm, and I'm interested in
+the 400-500mm range for width; the relief height is in the 20-30mm range depending on scale). I was
+imagining it would be carved with contour cuts in some thick nice ply, though I'm happy to hear
+better ideas; I have literally no experience with making something like this.
+
+(NOTE: go back to email thread and summarize the back-and-forth over tooling)
+---------------------------------
+
+Note that the shop did the extra work anyway just because they were nice, and that he was glad when
+I told him it was a gift for my wife.
+
+
+Zulip dump from 10 days after initial contact:
+-----------------------------------
+It IS Mt. Shasta!
+
+After I made the mosaic out of the tiles I downloaded to cover the area, I masked it with an outline
+of the state that I downloaded from a California gov geo site, then used a program called
+gdal_translate to turn the image, a "geotiff" file with height data encoded, into that heightmap png
+with the lowest value mapped to 0 and the highest to maxint.
+
+I also had to reproject the geotiff with the height data into the same coordinate system as the
+state outline was in. The height data was in a system using lat/long called "EPSG:4326", while the
+state outline was made from line segments with 2d vertices in a projected coordinate system called
+"EPSG:3857" with units of "meters". 3857 is "web Mercator", and is the coordinate system used by
+Google and Open Street Map for their map tiles and other shapes.
+
+It may or may not be surprising that cartography is very complicated!
+
+My next step is to turn this heightmap into solid geometry that I can 3d print and/or send to a
+local CNC shop to have them carve a relief of California out of wood, which is close to the final
+step of producing an artifact as a present for my partner.
+
+There are a bunch of python packages for working in this domain, but they're all just wrappers
+around various GDAL libraries or tools.
+
+The raw topo data I got from
+https://portal.opentopography.org/raster?opentopoID=OTSRTM.082015.4326.1 (that was the epsg 4326
+geocoded tiff; actually, several of them because you can only download up to 450km^2 at a time,
+hence having to mosaic them with the gdal_merge.py command (the '.py' is in the name of the command
+that gets installed when you do apt install gdal-bin)), then use gdalwarp to re-project to 3857,
+then I had to write a python program to mask it for some reason, then gdal_translate (no .py on that
+one, but they're all just python scripts) to convert to the png heightmap. I'm leaving out a couple
+details in the workflow, but that's the main shape of it.
+
+OK, actually, now that all that context is established, here's the actual command that produced that
+file from the geocoded tiff:
+
+gdal_translate -of PNG -ot UInt16 -scale -130 4412 0 65535 cropped_ca_topo.tif heightmap_cropped.png
+
+and then I used convert (the imagemagick program) to scale the png from 33,311x38,434 to
+2,000x2,2308 pixels.
+
+the -scale -130 4412 0 65535 is mapping the height data min/max to the png whiteness in the output
+file.
+---------------------------------------
+
+Zulip musings from a few days after that, still working on the heightmap:
+---------------------------------------
+(re: non-linear scaling of height to reduce pointiness)
+ok, it was easier than I thought it would be. gdal_translate has a -exponent flag you can use with
+-scale, so I remade the heightmap with an exponential scaling, using 0.41 as the exponent.
+
+funny enough, I'm still working on this, since even when I drastically scale the size of the mesh
+down in Blender (which I export to OBJ for import by FreeCAD), doing anything like modelling (eg,
+extruding downward or joining with a solid base, or cutting the shape so it's CA-shaped and not a
+rectangle) requires tens of gigabytes of resident memory and I keep having to kill the program and
+start over.
+
+a 60-megabyte OBJ file turns into 21 GB of resident data in the modelling software.
+
+I have 32GB of RAM installed
+
+that 21GB expands to 30 when I try manipulating it
+------------------------------------------
+
+Zulip from two weeks later (July 7):
+--------------------------------------
+
+Two weeks later I'm finally printing something out. I've given up on converting it into a parametric
+CAD-like object; it seems this is a Hard Problem, but I'm not sure why. My goal with doing that was
+to give a parametric CAD file to a local CNC milling shop, per their request, since when I suggested
+a mesh-based file (STL), the guy was like "I can't do much manipulation with that to make it more
+manufacturable, so a real CAD file would be best".
+
+But at least with an STL file, I can print it myself. So that's going now, we'll see how it turns
+out in no less than eight hours.
+
+I haven't really done anything else with my computer besides this for a while.
+
+(next day)
+ok, I got something printed out, but I'm not super stoked on it. Also, I'm still chasing the elusive
+dream of turning this into a parametric solid for easier CNCing. Vape pen for scale:
+(insert shitty print photo)
+
+(next day after that, the 9th)
+I've finally "finished": I've created a mesh that has no missing faces, is not too crazy, and can be
+converted into a parametric solid, and sent that off to a local CNC shop for a quote on having it
+routed out of wood. I'll also do another 3D print, since the base is now a larger version of the
+coastline instead of a rectangle, and the high frequency detail is a little diminished.
+
+----------------------------------------
+
+Links:
+
+https://data.ca.gov/
+
+https://portal.opentopography.org/raster?opentopoID=OTSRTM.082015.4326.1
+
+https://www.printables.com/model/240867-topographic-california
+
+https://touchterrain.geol.iastate.edu/
+
+https://en.wikipedia.org/wiki/Shuttle_Radar_Topography_Mission
+

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