crosstech-impl-speckle-blender

crosstech-impl-speckle-blender

Quick Reference

Technology Boundary

Aspect	Side A: Speckle	Side B: Blender
Data model	Base object graph (hash-based, immutable)	bpy.data collections (mutable, ID blocks)
Geometry	Mesh, Curve, Polycurve, Point, NURBS	Mesh, Bezier Curve, NURBS Curve, Empty
Materials	RenderMaterial (diffuse, opacity, metalness, roughness)	Principled BSDF node tree (full PBR)
Hierarchy	Collection with elements list	bpy.data.collections with linked objects
Units	String property on Base (mm, m, cm)	Scene unit system (bpy.context.scene.unit_settings)
Storage	Server, SQLite cache, Memory transport	.blend file (binary)
Versions	Speckle Server 2.x / 3.x, SpecklePy 2.x	Blender 3.x / 4.x

The Bridge: Speckle Blender Connector

The Speckle Blender connector is a Blender add-on that converts between Speckle Base objects and Blender data blocks. It uses SpecklePy internally for transport and serialization.

Direction	What Happens
Blender -> Speckle (Send)	Mesh/Curve data extracted from bpy.data, materials reduced to RenderMaterial, collections mapped to Speckle Collections
Speckle -> Blender (Receive)	Base objects converted to bpy.data.meshes/curves, RenderMaterials recreated as Principled BSDF, Collections mapped to bpy.data.collections

Supported Conversions

Blender Type	Speckle Type	Direction
Mesh	Mesh	Bidirectional
Bezier Curve	Curve / Polycurve	Bidirectional
NURBS Curve	Curve / Polycurve	Bidirectional
Empty / Collection	Collection	Bidirectional
Material (Principled BSDF)	RenderMaterial	Bidirectional

Critical Warnings

NEVER expect full IFC fidelity through Speckle -- Speckle transmits geometry and basic properties, NOT parametric definitions or IFC relationships.

NEVER assume complex Blender shader node trees survive the round-trip -- only the first Principled BSDF node's basic parameters (diffuse color, opacity, metalness, roughness) are extracted.

NEVER rely on Bonsai/IFC metadata surviving a Speckle round-trip -- Bonsai's native IFC object model is richer than Speckle's Base representation.

ALWAYS verify unit settings match between Speckle and Blender before send/receive -- unit mismatch causes geometry scaling errors.

ALWAYS use applicationId tracking when updating previously received models -- this prevents duplicate objects on subsequent receives.

---

Side A: Speckle Data Model

Base Object Fundamentals

Every object in Speckle inherits from Base. Key properties:

Property	Type	Purpose
id	string	Hash-based unique ID (content-addressable)
applicationId	string	Host application identity (enables update tracking)
speckle_type	string	Type discriminator
units	string	Unit system for geometry values
displayValue	List[Mesh]	Visual representation meshes

Speckle Collections

Collections represent hierarchical groupings:

from specklepy.objects import Base
from specklepy.objects.other import Collection

root = Collection(name="Building", collectionType="model")
level1 = Collection(name="Level 1", collectionType="level")
root.elements = [level1]
level1.elements = [wall_obj, door_obj]

Collections MUST form a directed tree -- no cycles allowed.

RenderMaterial

from specklepy.objects.other import RenderMaterial

mat = RenderMaterial()
mat.name = "Concrete"
mat.diffuse = 0xFFA0A0A0   # ARGB integer
mat.opacity = 1.0
mat.metalness = 0.0
mat.roughness = 0.8

CRITICAL: RenderMaterial supports ONLY diffuse color, opacity, metalness, and roughness. Texture maps, normal maps, emission, subsurface scattering, and all other PBR channels are NOT supported.

Proxy Collections (v3)

In Speckle v3, organizational data is stored at the root level as proxy collections:

• renderMaterialProxies -- material assignments
• levelProxies -- building levels
• instanceDefinitionProxies -- block/component definitions

Each proxy references objects by applicationId, requiring a two-step lookup.

---

Side B: Blender Data Model

Relevant bpy.data Collections

Collection	Type	Maps To
bpy.data.meshes	Mesh geometry	Speckle Mesh
bpy.data.curves	Bezier/NURBS curves	Speckle Curve/Polycurve
bpy.data.objects	Object wrappers	Speckle Base with displayValue
bpy.data.collections	Hierarchy groups	Speckle Collection
bpy.data.materials	Shader node trees	Speckle RenderMaterial

Blender Material Structure

A Blender Principled BSDF material exposes ~20+ parameters. The Speckle connector extracts ONLY:

Principled BSDF Input	RenderMaterial Property	Preserved?
Base Color	diffuse	YES
Alpha	opacity	YES
Metallic	metalness	YES
Roughness	roughness	YES
Normal Map	--	NO
Emission	--	NO
Subsurface	--	NO
Specular	--	NO
All texture nodes	--	NO

---

The Bridge: Send/Receive Workflows

Workflow 1: Send from Blender to Speckle (Connector UI)

1. Open the Speckle panel in Blender sidebar
2. Authenticate with your Speckle account
3. Select the project and model (branch)
4. Choose objects to send (selection, collection, or all)
5. Click Send -- the connector converts Blender data to Base objects and pushes to the server

Workflow 2: Receive from Speckle into Blender (Connector UI)

1. Open the Speckle panel in Blender sidebar
2. Select the project, model, and version to receive
3. Click Receive -- the connector downloads Base objects and converts to Blender data
4. Objects appear in a new collection named after the model

Workflow 3: SpecklePy Programmatic Send

import bpy
from specklepy.objects import Base
from specklepy.objects.geometry import Mesh as SpeckleMesh
from specklepy.transports.server import ServerTransport
from specklepy.api import operations
from specklepy.api.client import SpeckleClient
from specklepy.api.credentials import get_default_account

# Authenticate
client = SpeckleClient(host="https://app.speckle.systems")
account = get_default_account()
client.authenticate_with_account(account)

# Extract mesh data from Blender
bl_obj = bpy.data.objects["MyObject"]
bl_mesh = bl_obj.data
bl_mesh.calc_loop_triangles()

vertices = []
for v in bl_mesh.vertices:
    vertices.extend([v.co.x, v.co.y, v.co.z])

faces = []
for tri in bl_mesh.loop_triangles:
    faces.append(3)  # triangle face count
    faces.extend(tri.vertices)

# Create Speckle Mesh
spk_mesh = SpeckleMesh()
spk_mesh.vertices = vertices
spk_mesh.faces = faces
spk_mesh.units = "m"

# Send
transport = ServerTransport(client=client, stream_id="your_stream_id")
obj_hash = operations.send(base=spk_mesh, transports=[transport])

# Create version
commit_id = client.commit.create(
    stream_id="your_stream_id",
    object_id=obj_hash,
    message="Blender mesh export"
)

Workflow 4: SpecklePy Programmatic Receive

from specklepy.transports.server import ServerTransport
from specklepy.api import operations

transport = ServerTransport(client=client, stream_id="your_stream_id")

# Get latest commit
commits = client.commit.list("your_stream_id", limit=1)
latest = commits[0]

# Receive object graph
received = operations.receive(
    obj_id=latest.referencedObject,
    remote_transport=transport
)

# Convert to Blender mesh
def speckle_mesh_to_blender(spk_mesh, name="SpeckleImport"):
    verts = []
    for i in range(0, len(spk_mesh.vertices), 3):
        verts.append((
            spk_mesh.vertices[i],
            spk_mesh.vertices[i + 1],
            spk_mesh.vertices[i + 2]
        ))

    faces = []
    idx = 0
    while idx < len(spk_mesh.faces):
        n = spk_mesh.faces[idx]
        face = tuple(spk_mesh.faces[idx + 1 : idx + 1 + n])
        faces.append(face)
        idx += n + 1

    mesh = bpy.data.meshes.new(name)
    mesh.from_pydata(verts, [], faces)
    mesh.update()

    obj = bpy.data.objects.new(name, mesh)
    bpy.context.collection.objects.link(obj)
    return obj

---

IFC Data Through Speckle

One-Way Limitation: Bonsai -> Speckle (Send Only)

The IFC/Bonsai to Speckle workflow is ONE-DIRECTIONAL:

Direction	Status	Result
Bonsai -> Speckle (Send)	WORKS	IFC elements sent as Speckle Base objects with geometry + basic properties
Speckle -> Bonsai (Receive)	DOES NOT WORK	Received objects are plain Blender meshes, NOT recognized as IFC elements by Bonsai

What Transfers (IFC -> Speckle -> Blender)

IFC Data	Transferred?	Notes
Mesh geometry	YES	Triangulated during conversion
Material assignments	YES	Basic properties only (diffuse, opacity)
Spatial hierarchy	YES	Mapped to Speckle Collections -> Blender collections
Basic property sets	PARTIAL	Flattened to dynamic properties on Base
IfcRelAggregates	NO	Relationship semantics lost
IfcRelContainedInSpatialStructure	NO	Spatial containment details lost
Parametric definitions	NO	Only display mesh transferred
Bonsai editing capability	NO	Cannot edit as IFC after round-trip

Data Loss Decision Tree

Is full IFC fidelity required?
├── YES → Do NOT use Speckle as transport. Use native IFC files directly.
└── NO → Is visual review sufficient?
    ├── YES → Speckle is appropriate. Geometry + basic materials transfer.
    └── NO → Do you need property data?
        ├── YES (basic props) → Speckle works. Properties flatten but transfer.
        └── YES (full psets) → Use IFC files directly or IfcOpenShell.

---

Collection Structure Mapping

Blender -> Speckle

Blender Scene Collection           Speckle Root Collection
├── Building                  →    ├── Collection("Building")
│   ├── Level 1               →    │   ├── Collection("Level 1")
│   │   ├── Wall.001          →    │   │   ├── Base(displayValue=[Mesh])
│   │   └── Door.001          →    │   │   └── Base(displayValue=[Mesh])
│   └── Level 2               →    │   └── Collection("Level 2")
└── Site                      →    └── Collection("Site")

Speckle -> Blender

On receive, the connector creates a root collection named [ProjectName] - [ModelName]. All received objects are placed inside, preserving the source hierarchy.

---

Round-Trip Data Integrity

What SURVIVES Blender -> Speckle -> Blender

• Mesh vertex positions and face topology
• Basic material properties (diffuse, opacity, metalness, roughness)
• Collection hierarchy and object names
• Object transforms (location, rotation, scale)

What is LOST or DEGRADED

• Complex shader node trees (reduced to single Principled BSDF parameters)
• Texture maps and UV-linked images
• Modifiers (ALWAYS apply modifiers before sending)
• Shape keys / blend shapes
• Particle systems
• Physics simulations
• Constraints and drivers
• Custom properties on objects (use Speckle dynamic properties instead)
• Vertex groups (partial support)

ALWAYS apply all modifiers before sending if the modified geometry is needed. The connector reads the evaluated mesh, but modifier stacks are NOT preserved.

---

Unit Handling

Blender Unit	Speckle Unit String	Notes
Meters	"m"	Default for architectural scenes
Millimeters	"mm"	Common for BIM data from Revit
Centimeters	"cm"
None	"m"	Blender defaults to meters when unit system is "None"

ALWAYS set bpy.context.scene.unit_settings.length_unit to match the expected Speckle data units before receiving. Unit mismatch causes geometry to appear at wrong scale.

---

Reference Links

• references/methods.md -- SpecklePy API methods and Blender connector operations
• references/examples.md -- Working code examples for common workflows
• references/anti-patterns.md -- What NOT to do at the Speckle-Blender boundary

Official Sources

• https://speckle.guide/user/blender.html
• https://speckle.systems/docs/developer/python
• https://specklepy.readthedocs.io/
• https://docs.blender.org/api/current/
• https://github.com/specklesystems/speckle-blender