Utility_Apps/Blender/addons/Mesh Outline Projector

Mesh Outline Projector

A Blender addon that projects the vertical outline of selected objects onto a target mesh and transfers materials, perfect for architectural visualization and terrain mapping.

Overview

Mesh Outline Projector takes the 2D silhouette of objects (when viewed from above) and "stamps" them onto a mesh below, automatically cutting the mesh and applying the source object's material to the projected area. Think of it as a cookie-cutter that works vertically through 3D space.

Key Features

• Vertical Projection: Projects object outlines straight down (Z-axis) onto target surfaces
• Material Transfer: Automatically applies source object materials to projected regions
• Clean Cutting: Uses Blender's knife project for precise edge creation
• Smart Material Assignment: Point-in-polygon detection with edge tolerance for accurate coverage
• Mesh Cleanup: Automatically removes previous cuts with Limit Dissolve
• Intersection Detection: Validates that objects actually overlap before processing
• Multiple Objects: Process multiple source objects in a single operation

Installation

1. Download mesh_outline_projector.py
2. Open Blender → Edit → Preferences → Add-ons
3. Click "Install..." and select the downloaded file
4. Enable "Mesh: Mesh Outline Projector" in the add-ons list
5. The panel appears in the 3D Viewport sidebar under the "Outline Projector" tab

Quick Start

Basic Workflow

1. Setup Scene

   • Position your source objects (e.g., building footprints) above your target mesh (e.g., terrain)
   • Objects can be at any height - only horizontal (XY) overlap matters

2. Select Objects

   • Select one or more source objects (the objects whose outlines you want to project)
   • Select the target mesh last (it becomes the active object - shown in orange)

3. Set View

   • Press Numpad 7 to switch to top orthographic view
   • This is required for knife project to work correctly

4. Run Operator

   • Open the sidebar (N key) → "Outline Projector" tab
   • Adjust settings if needed (see below)
   • Click "Project Outline"

What Happens

The addon performs these steps automatically:

1. Validates that source objects overlap with target in XY plane
2. Cleans up the target mesh (Limit Dissolve + Quads to Tris)
3. Resets materials to the first material slot
4. For each source object:
   • Extracts the horizontal perimeter edges (2D outline)
   • Creates a temporary curve from these edges
   • Uses knife project to cut the target mesh
   • Assigns the source material to faces within the projected area
5. Reports results with detailed console output

Settings

Dissolve Angle

• Default: 0.04 degrees
• Range: 0.0 - 5.0 degrees
• Purpose: Controls how aggressively Limit Dissolve removes edges from previous operations

When to adjust:

• Increase (0.5-2.0°) if working with curved or organic surfaces
• Keep low (0.01-0.1°) for architectural/flat surfaces
• Higher values = more aggressive cleanup, fewer edges

Edge Tolerance

• Default: 0.05 units
• Range: 0.0 - 1.0 units
• Purpose: How close a vertex must be to a polygon edge to be considered "on the edge"

When to adjust:

• Increase (0.1-0.5) if missing faces at the boundaries
• Decrease (0.01-0.03) if getting material bleeding outside the outline
• Affects the precision of material assignment at polygon boundaries

Use Cases

Architectural Site Plans

Project building footprints onto terrain meshes:

• Import IFC building models
• Create terrain mesh from topography data
• Project building outlines to create material zones

Terrain Texturing

Stamp different material zones onto landscapes:

• Roads, paths, and sidewalks
• Water bodies and wetlands
• Vegetation zones
• Building pads

Urban Planning

Visualize zoning and land use:

• Different materials for residential/commercial/industrial zones
• Overlay multiple boundary shapes
• Iterate quickly as plans change

Tips & Best Practices

Before Running

✅ Do:

• Ensure source objects are above or at the same level as target mesh
• Use simple, clean geometry for source objects
• Press Numpad 7 (top view) before running
• Save your work before first use

❌ Don't:

• Use extremely complex source meshes (simplify first)
• Forget to set top view
• Run on unsaved files (though Undo works)

Iteration Workflow

The addon is designed for iteration:

1. Run projection with objects A and B
2. Adjust position/scale of object A
3. Run projection again - mesh is automatically cleaned up
4. Materials from both objects are preserved

The mesh reset happens automatically - you can run the operator multiple times without manual cleanup.

Material Management

• The addon preserves the first material slot as the "base" material
• Source materials are added as new slots (slot 1, 2, 3, etc.)
• Each run resets everything to the base material before applying projections
• If you want a different base material, assign it to slot 0 before running

Troubleshooting

"No source objects intersect with target mesh"

Problem: Objects don't overlap in the XY plane (when viewed from above)

Solutions:

• Check bounding boxes in debug output
• Move objects horizontally to overlap
• Objects can be at different Z heights - that's fine
• Ensure you're not selecting the target as a source object

Materials not appearing correctly

Problem: Materials bleeding outside boundaries or missing at edges

Solutions:

• Adjust Edge Tolerance setting
• Increase if missing edge faces (try 0.1-0.2)
• Decrease if bleeding outside (try 0.02-0.03)
• Check that source objects have materials assigned

Blender crashes

Problem: Crash during operation (rare)

Solutions:

• Ensure you're in top orthographic view (Numpad 7)
• Simplify source mesh geometry
• Update to latest Blender version
• Check console for error messages

Unexpected results after multiple runs

Problem: Results look different on subsequent runs

Solutions:

• This is normal - each run subdivides the mesh differently
• Knife project creates new edges each time
• Undo (Ctrl+Z) to return to previous state
• The dissolve/cleanup helps but won't make mesh identical

Technical Details

How Outline Detection Works

The addon uses three methods to find outline edges:

1. Boundary edges: Edges with only one connected face
2. Silhouette edges: Edges where connected faces have different vertical orientations
3. Perimeter edges: Vertical edges at the outer boundary

These are combined to form the complete 2D outline when viewed from above.

Material Assignment Algorithm

1. Extract horizontal edges from the 3D outline
2. Build a 2D polygon from these edges (in world XY space)
3. For each face in the target mesh:
   • Check if all vertices are inside the polygon OR near an edge
   • Uses ray-casting for point-in-polygon test
   • Uses perpendicular distance for edge proximity
4. Assign material only if all vertices pass

This ensures clean boundaries without bleeding.

Known Limitations

• Requires top orthographic view (Numpad 7) to work correctly
• Works best with relatively flat target meshes
• Very dense meshes may slow down processing
• Complex source geometry may produce unexpected outlines
• Knife project can create overlapping edges in some cases
• Z-axis projection only - cannot project at angles