Add STEP Import for Assemblies

[jmwright]

The goal is to make it possible to round-trip assemblies to and from STEP without loss of data. This data can include:

• Part location
• Part color
• Shape colors
• Shape colors
• Shape names (advanced face)

Fixes #826 and #1427

[codecov]

Codecov Report

❌ Patch coverage is 96.56160% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.06%. Comparing base (8431073) to head (315cce7).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
cadquery/occ_impl/importers/assembly.py	96.29%	1 Missing and 5 partials ⚠️
cadquery/occ_impl/assembly.py	93.93%	0 Missing and 4 partials ⚠️
cadquery/assembly.py	97.59%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1779      +/-   ##
==========================================
+ Coverage   95.66%   96.06%   +0.39%     
==========================================
  Files          28       30       +2     
  Lines        7431     9444    +2013     
  Branches     1122     1562     +440     
==========================================
+ Hits         7109     9072    +1963     
- Misses        193      226      +33     
- Partials      129      146      +17     

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[jmwright]

@adam-urbanczyk In 4045c58 you set the cadquery.Assembly.importStep method up to be a class method, and you construct assy before calling the lower-level method. However, since the Assembly.name property is private and can only be set during instantiation, this creates an issue for me. I need to be able to set the top-level assembly name based on the name set in the STEP file, which requires me to set the name property after instantiation.

We need to decide on the proper way to fix this.

[adam-urbanczyk]

Hey, I do not understand the issue. You can always do this:

assy = Assembly()
assy.name = '123'

Do you mean that you need to modify AssemblyProtocol to satisify mypy? That also does not sound like an issue to me.

[jmwright]

Correct, mypy complains. I can make that change to make name a public property if you don't see an issue with doing so.

[adam-urbanczyk]

I found one more issue: import did not update the fist key in .objects properly. It is fixed and tested now.

[jon-proximafusion]

Just tinkering with this and noticed the file sizes appear to be different to the original step file, am I doing something wrong here.

I have installed this branch with pip

pip install git+https://github.com/CadQuery/cadquery.git@assembly-import

import cadquery as cq
sphere = cq.Workplane().sphere(5.0)

assembly = cq.Assembly()
assembly.add(sphere, name="sphere")
assembly.export("sphere.step")

assembly2 = cq.Assembly()
assembly2.importStep("sphere.step")
assembly2.save("sphere2.step")
assembly2.export("sphere3.step")

Filesize appears to be quite different, is some content being missed when importing and saving again

ll
-rw-rw-r--  1 jon jon 3254 Sep 12 13:43 sphere2.step
-rw-rw-r--  1 jon jon 3254 Sep 12 13:43 sphere3.step
-rw-rw-r--  1 jon jon 6703 Sep 12 13:43 sphere.step

[adam-urbanczyk]

Weird, something is definitely off here

[adam-urbanczyk]

Note that load is a static class method and it creates a new assembly:

import cadquery as cq
sphere = cq.Workplane().sphere(5.0)

assembly = cq.Assembly()
assembly.add(sphere, name="sphere")
assembly.export("sphere.step")

assembly2 = Assembly.load("sphere.step")
assembly2.save("sphere2.step")
assembly2.export("sphere3.step")

!ls -l *sphere*.step
-rw-r--r-- 1  197609 6706 Sep 12 14:58 sphere.step
-rw-r--r-- 1  197609 6690 Sep 12 15:01 sphere2.step
-rw-r--r-- 1  197609 6690 Sep 12 15:01 sphere3.step

[lorenzncode]

I captured timing for export/load and step file size. These are only observations and perhaps are expected behavior.

• load can be slow with many objects.
• There seems to be significant file size difference in the reexport.

# 10k boxes example from PR 1157

import cadquery as cq
import timeit
import os

box = cq.Workplane().box(1, 1, 1)

assy = cq.Assembly()
num = 100
for i in range(1, num + 1, 1):
    for j in range(1, num + 1, 1):
        assy.add(
            box,
            name=f"box{i}_{j}",
            color=cq.Color("red"),
            loc=cq.Location((1.1 * i, 1.1 * j, 0)),
        )

# export the assembly to step
tsave = timeit.timeit('assy.export("test1.step")', globals=globals(), number=1)

# load the step
result = []


def timed_load():
    result.append(assy.load("test1.step"))


tload = timeit.timeit("timed_load()", globals=globals(), number=1)

# reexport to check file size
result[0].export("test2.step")

print(f"time export: {tsave:.1f} s")
print(f"time load: {tload:.1f} s")

print(
    f"original test1.step size: {os.path.getsize('test1.step') / (1024 * 1024):.2f} MB"
)
print(
    f"reexport test2.step size: {os.path.getsize('test2.step') / (1024 * 1024):.2f} MB"
)

(I am on a faster machine which explains the <2s export vs previous result with ~5s export)

time export: 1.5 s
time load: 29.3 s
original test1.step size: 21.92 MB
reexport test2.step size: 38.22 MB

[adam-urbanczyk]

FYI: I did quite some rework. Will explain later.

[adam-urbanczyk]

• Added xbf and xml support
• Got rid of extra nodes as much as possible
• Round trips require different handling of colors; colors should only be used on leaf nodes
• Fixed color handling for roundtrips (srgb vs linear rgb)
• There are still some strange issues here and there, but typical use cases seem to work reliably:
  • Copies and multiple nesting results in wrong instance names when exporting to STEP (see Possible bug: XDE export to STEP - some instance names are lost Open-Cascade-SAS/OCCT#726)
  • XML export seems to distort colors (XBF does not)

[adam-urbanczyk]

Additionally, I tweaked the docs a little bit.