How to load a WaveFront (.obj) model

This guide shows how to import a WaveFront .obj model into a Radiance scene, assign materials, build an octree, and trace rays through it.

Convert .obj to Radiance

Use obj2rad() to convert a .obj file to a Radiance scene description. The result is returned as bytes.

import pyradiance as pr

room_rad = pr.obj2rad("room.obj")

Inspect the modifiers

The converted scene will contain surfaces that reference modifiers (material names) that need to be defined. Use parse_primitive() to extract the primitives from the bytes and collect the unique modifier names:

primitives = pr.parse_primitive(room_rad)
modifiers = {p.modifier for p in primitives}
print(modifiers)

Alternatively, use obj2rad() with quallist=True to get just the list of qualifiers (modifier names) without producing a full scene description:

qualifiers = pr.obj2rad("room.obj", quallist=True).decode().splitlines()
print(qualifiers)

Define materials

Create a Primitive for each modifier. A diffuse plastic material takes five real arguments: R, G, B reflectances, specularity, and roughness.

materials = [
    pr.Primitive("void", "plastic", "floor",   [], [0.3, 0.3, 0.3, 0, 0]),
    pr.Primitive("void", "plastic", "walls",   [], [0.5, 0.5, 0.5, 0, 0]),
    pr.Primitive("void", "plastic", "ceiling", [], [0.8, 0.8, 0.8, 0, 0]),
]

Build an octree

Serialize the material primitives to bytes and pass them together with the geometry bytes to oconv() via stdin. Both streams are concatenated before being piped to oconv:

mat_bytes = b"".join(m.bytes for m in materials)
stdin_bytes = mat_bytes + room_rad

oct = pr.oconv(stdin=stdin_bytes)

# Write the octree to disk
with open("room.oct", "wb") as f:
    f.write(oct)

Trace a ray

Pass input rays as bytes to rtrace(). Each ray is a line of six space-separated floats: ox oy oz dx dy dz.

rays = b"0 1 1.5 0 0 1\n"
result = pr.rtrace(rays, "room.oct", outspec="v")
print(result.decode())

The outspec="v" argument requests radiance values (RGB) at each intersection. See help(pr.rtrace) for the full list of output specifiers and options.