Saturday, March 2, 2024

Marcos Dione: automating-blender-based-hillshading-with-python


Bear in mind my Mix based mostly hillshading? I
promised to attempt to automate it, proper? Properly, it appears I’ve the curiosity and stamina now, so that is what I am doing.
However girls and boys and something in between and past, the stamina is waning and the wrongdoer is Blender’s internals
being uncovered right into a non-Pythonic API[3]. I swear if I labored in something remotely near this, I might be writing a
wrapper for all this. However within the meantime, it is all a discovery path to one thing that doesn’t resemble a
hack. Simply learn a few of
Blender’s Python Quickstart:

When you find yourself acquainted with different Python APIs it’s possible you’ll be shocked that new data-blocks within the bpy API can’t be
created by calling the category:

bpy.sorts.Mesh()
Traceback (most up-to-date name final):
File "<blender_console>", line 1, in <module>
<span class="createlink">TypeError</span>: bpy_struct.__new__(sort): anticipated a single argument

That is an intentional a part of the API design. The Blender Python API can’t create Blender knowledge that exists exterior
the principle Blender database (accessed by way of bpy.knowledge), as a result of this knowledge is managed by Blender (save, load, undo,
append, and so on).

Information is added and eliminated through strategies on the collections in bpy.knowledge, e.g:

mesh = bpy.knowledge.meshes.new(identify="MyMesh")

That’s, as a substitute of constructing the constructor name this inner API, they make it fail miserably and pressure you to make use of the
inner API! At present I used to be mentioning that Asterisk’s programming language was positively designed by a
Telecommunications Engineer, so I suppose this one was designed by a 3D artist? However I digress…

One of many very first thing about Blender’s internals is that one solution to work is predicated on Contexts. This is sensible when
growing plugins, the place you principally want to use issues to the
chosen object, however for somebody actually constructing all the pieces from scratch like I have to, it feels bizarre.

One of many benefits is that you may open a Python console and let Blender present you the calls it makes for each step
you make on the UI, nevertheless it’s so context based mostly that the outcomes is ineffective as a script. Or as an illustration, linking the
output of a factor into he the enter of one other is registered as a drag-and-drop name that features the gap the
mouse moved through the drag, so it is relative of the output dot the place you began and what it hyperlinks to additionally relies on
the bodily and never logical place of the stuff you’re linking,

bpy.ops.node.hyperlink(detach=False, drag_start=(583.898, 257.74))

It takes various digging round in a not very pleasant REPL[1] with restricted scrollback and
not a lot documentation to search out extra reproducible, much less context dependent options. That is what’s consuming up my
stamina, it isn’t so enjoyable anymore. Paraphrasing somebody on Mastodon: What use is a pleasant piece of Open Software program if it is
documentation shouldn’t be sufficient to be helpful[2]?

One other essential factor is that every one objects have two views: one which has generic properties like place and
rotation, which could be reacheched by bpy.knowledge.objects; and one which has particular properties like a lightweight’s energy or a
digital camera’s lens angle, which could be reached by f.i. bpy.knowledge.cameras. This was totally complicated, specifically since
all bpy.knowledge‘s documentation is 4 traces lengthy. Later I came upon you may get particular knowledge from the generic one in
the .knowledge attribute, so the take out is: all the time get your objects from bpy.knowledge.objects.

As soon as we recover from that challenge, issues are fairly simple, however not essentially straightforward. The script as it’s can already
be used with blender --background --python <script_file>, however have in account that if you do this, you begin with
the default generic 3D setup, with a lightweight, a digital camera and a dice. It’s a must to delete the dice, however you may get a
reference to the opposite two to reuse them.

Then comes the executive stuff round simply rendering the scene. To industrialize it and be capable of rapidly check
stuff, you’ll be able to attempt to get command line choices. You should use Python’s argparser module for this, however have in account
that these --background --python blender.py choices are going to be handed to the script, so that you both ignore unknown
choices otherwise you declare these too:

mdione@ioniq:~/src/tasks/elevation$ blender --background --python blender.py
Blender 3.6.2
Learn prefs: "/dwelling/mdione/.config/blender/3.6/config/userpref.mix"
utilization: blender [-h] [--render-samples RENDER_SAMPLES] [--render-scale RENDER_SCALE] [--height-scale HEIGHT_SCALE] FILE
blender: error: unrecognized arguments: --background --python

Additionally, these choices are going to be handed to Blender! So on the finish of your run, Blender goes to complain that it
would not perceive your choices:

unknown argument, loading as file: --render-samples
Error: Can't learn file "/dwelling/mdione/src/tasks/elevation/--render-samples": No such file or listing
Blender stop

The opposite step you must do is to repeat the Geo a part of GeoTIFF to the output file. I used rasterio, principally as a result of at
first I attempted gdal (I used to be already utilizing gdal_edit.py to do that in my earlier handbook process), nevertheless it’s API was
fairly complicated and rasterio‘s is extra plain. However, rasterio cannot really open a file simply to write down the metadata
like gdal does, so I needed to open the output file, learn all knowledge, open it once more for writing (this truncates the file)
and write metadata and knowledge.

Now, some caveats. First, as I superior in my final submit, the strategy as it’s proper now has points on the seams. Blender
cannot learn GDAL VRT recordsdata, so both I construct 9 planes as a substitute of 1 (all the neighbors are wanted to correctly
calculate the shadows as a result of Blender can also be taking in account gentle mirrored again from different options, that means
mountains) or for every 1×1 tile I generate one other with some buffer. I’ll strive the primary one and see if it fixes this
challenge with out a lot runtime impression.

Second, the script shouldn’t be 100% parametrized. Solar dimension and energy are fastened based mostly on my checks. Perhaps sooner or later. Third,
I’ll attempt to add a scattering sky, so we get a bluish tint to the shadows, and set the Solar’s coloration to one thing
yellowish. These ought to most likely be choices too.

Fourth, and doubtless most essential. I found that this hillshading methodology is absolutely smart to lacking or unhealthy knowledge,
as a result of they appear to be darkish, deep holes. That is most likely a deal breaker for a lot of, so that you both repair your knowledge, otherwise you
seek for higher knowledge, otherwise you dwell with it. I am unsure what I will do.

So, what did I do with this? Properly, first, discover good parameters, one for render samples and one other for peak scale.
Render time grows principally linearly with render samples, so I simply looked for the one earlier than element stopped showing;
the worth I discovered was 120 samples.
Once we left off I used to be utilizing 10 as a substitute of 5 for peak scale, nevertheless it appears too exaggerated on hills (nevertheless it appears
AWESOME in mountains just like the Mount Blanc/Monte Bianco! See under), so I attempted to pinpoint an excellent stability. For me it is 8,
perhaps 7.

Why get these values proper? As a result of like I discussed earlier than, a single 1×1°, 3601x5137px tile takes some 40m in my laptop computer
at 100 samples, so the extra tuned the higher. One good solution to rapidly check is to decrease the samples or use the
--render-scale possibility of the script to scale back the scale of the output. Word that since you scale back each dimensions at
the identical time, the ultimate render (and the time that takes) is definitely the sq. of this issue: 50% is definitely 25%
(as a result of 0.50 * 0.50 = 0.25).

So, with out additional addo, this is my script. When you discover it helpful however need extra energy, open points or PRs, all the pieces
is welcome.

https://github.com/StyXman/blender_hilllshading [5]

Attempt to use the important department; develop is taken into account unstable and could be damaged.

A few pictures of the shadows utilized to my model as teaser, each utilizing solely 20 samples and x10 peak scale:

Dhaulagiri:

Mont Blanc/Monte Bianco:

Man, I really like the truth that the tail of the Giacchiaio del Miage is in shadows, however the remaining shouldn’t be; or how
Monte Bianco/Mont Blanc’s shadow reaches throughout the valley to the bottom of los angeles Tête d’Arp. But in addition discover the unhealthy knowledge
near la Mer de Glace.


blender python openstreemap gdal elevation hillshading rasterio gis dem


[1] Okay, TBH right here, I am very a lot used to ipython‘s console, it is actually nearer to the plain python one. No tab
completion, so plenty of calls to dir() and some assist()s.

[2] I could not discover it once more. Mastodon posts aren’t searchable by default, which I perceive is nice for privateness, however
alternatively the present shoppers do not retailer something domestically, so you’ll be able to’t even search what you already noticed.
I’ve a number of semi-ranting posts about this and I might present them to you, however they acquired misplaced on Mastodon. See what I
imply?

[3] So you have got an thought, this took me an entire week of free time to complete, together with however not within the textual content, my previous nemesis,
terracing impact. This factor is brittle.

[4] Yeah, perhaps the API is generally designed for this.

[5] My website generator retains breaking. That is the second time I’ve to publicly admit this. Perhaps subsequent weekend I will
collect steam and substitute it with nikola.

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