Step 2: Generate Projection¶

Purpose¶

Convert the loaded 3D scan into a 2D orthographic image that exposes the vault surface for segmentation and geometry work.

How projection works¶

Points are accumulated onto the image plane using a 1D Gaussian splat: each 3D point contributes intensity to its projected pixel weighted by a Gaussian function of its distance from the projection focal plane along the view axis.¹ Summing these weighted contributions across all points produces a smooth density image that fills small gaps between neighbouring points and reduces aliasing, giving clearer rib definition than a simple point-drop or max-depth render.

Choosing a perspective¶

Vault Analyser supports multiple orthographic viewpoints. The choice depends on which surface you are analysing:

Perspective	Use when
Bottom (intrados)	Analysing the underside of the vault — the usual starting point for rib geometry
Top (extrados)	Analysing the vault's upper surface
North / South / East / West	Analysing a particular elevation or section if the vault is not viewed from directly below

For most rib analysis, start with the Bottom Up projection.

What you do here¶

1. Select a projection perspective from the controls.
2. Set the resolution and any projection settings such as Gaussian spread if needed. Higher detail gives clearer outputs but takes longer.
3. Click Generate Projection and wait for the image to appear in the preview panel.
4. Inspect the result. Ribs and bosses should be readable enough for segmentation.
5. If needed, adjust the settings or try another viewpoint and generate again.
6. Keep at least one projection that you are confident using for Step 3.

Interface controls¶

Control	What it does
Perspective selector	Chooses the projection axis
Resolution / scale	Sets image size and output detail
Generate button	Triggers the projection computation
Preview panel	Displays the resulting 2D image

The Bottom Up perspective is selected by default. Click View more options beneath the perspective selector to reveal the remaining viewpoints (Top Down, North, South, East, West). The Display Settings bar in the preview panel is collapsed by default; expand it to adjust how many points are loaded for the interactive 3D preview and to reload the point cloud at a different density.

What to check before moving on¶

• The main rib pattern is visible.
• Boss locations can be identified.
• The image is not obviously clipped, blurred, or misleading.

Expected result¶

At least one usable saved projection ready for segmentation in Step 3.