Backfill misses¶

Recover the sky/miss points a scan needs for leaf area density — laser pulses that were fired but returned nothing because they passed through the canopy into open sky. See Scans for what misses are and why they matter.

LAD inverts Beer's law on the beams crossing each voxel, and the misses are the transmission denominator: without them there's no way to tell a voxel that stopped every beam from one that let them all through. Some formats record misses directly (E57, structured PLY); others drop them but keep enough to reconstruct them. Backfill Misses does that reconstruction once, up front, and stores the result on the scan so you can see it and reuse it.

When you need it¶

A scan has no sky/miss points (the "Show misses" toggle is absent in the Scans panel), and
it carries a per-return timestamp column and/or scan-grid row/column indices to rebuild the miss directions from.

If a scan already retains misses, there's nothing to do. If it has neither a timestamp nor a row/column grid, misses can't be recovered — re-import the scan in a format that keeps them (E57 / structured PLY).

Steps¶

Select the scan(s) in the Scans panel.
Click Backfill Misses in the Pre-processing group of the toolbar (cloud icon). A setup dialog opens listing the eligible scans, pre-selected from your current selection — like the Triangulation and Leaf Area Density dialogs. Scans that already have misses or can't recover them are noted but excluded.
Leave Show misses in the viewer after completion on to reveal the recovered points when it finishes (it's disabled automatically when the selected scans have no scanner origin, since misses can't be drawn without one — see the note below).
Click Backfill Misses. A progress bar shows the per-scan stages (reading the scan, building the cloud, reconstructing misses, storing); it can be cancelled. A summary toast reports how many points were recovered.
When Show misses was on, the "Show misses" toggle on each backfilled scan row turns on automatically and the recovered sky points are drawn (in a distinct colour, projected onto the scan's bounding sphere and streamed as a level-of-detail octree, so a dense sky shell stays smooth). Toggle it off once you've confirmed them.

You can also trigger backfill from the Leaf Area Density dialog: when a selected scan has no misses, Compute is disabled and a banner offers a one-click Backfill Misses button. See Estimate leaf area density.

Notes¶

Backfilling mutates the scan's session in place — it is not an undoable edit. Re-running it simply recomputes the misses.
The recovered misses are kept in a lightweight side buffer, separate from the scan's points, so a sparse scan that is mostly sky doesn't bloat memory. They aren't exported with the point cloud; they exist to drive (and let you verify) the LAD inversion.
Cropping a scan after backfilling marks the recovered misses stale. They were reconstructed against the pre-crop hits, so their hit/miss ratio no longer matches the surviving points. Phytograph keeps them but warns you — at crop time and again in the LAD result — to re-run Backfill Misses on the cropped cloud before estimating leaf-area density. (A crop never deletes sky/miss points themselves; it only removes hits.)
For moving-platform scans, each return's timestamp is joined to the platform trajectory to reconstruct a per-beam emission origin, so the recovered misses follow the flight path rather than fanning from a single static apex. (The row/column grid path doesn't apply to a moving sweep; a per-return timestamp is required.)