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Check Seed Lines

Algorithm details: Technical Guide → Check Seed Lines

What does this tool do?

Check Seed Lines cleans and prepares seed lines before downstream processing. It can:

  • normalize multipart lines to LineString
  • remove invalid/empty/degenerate geometries
  • optionally remove short lines
  • optionally clip lines to CHM valid-data footprint (with inward shrink)
  • optionally snap close endpoints (endpoint-only, directed snap)
  • split lines at intersections
  • optionally group lines and merge by group
  • optionally densify long lines by inserting internal vertices

How do I use it?

Quick Start

  1. Prepare your input files: a seed line vector file and a CHM raster file.
  2. Run the tool from the GUI: Check Seed Line

What options can I set?

  • Seed Line: Input seed line file
  • CHM Raster: Input raster used to build a valid-data footprint for clipping
  • CHM footprint shrink (m): Inward buffer distance in meters applied before clipping (default 15). Geographic CRS inputs are converted to a local meter-based projection for this step. See shrink-distance guide below.
  • Clip to CHM footprint: Enable/disable footprint clipping step (default true). If enabled and CHM raster is missing, clipping is skipped with an error message.
  • Output Seed Line: Output seed line file
  • Remove short lines: Enable removal of short segments
  • Minimum line length (m): Threshold in meters for short-line removal (default 5). Geographic CRS inputs are evaluated in a local meter-based projection for this step.
  • Snap close endpoints: Enable endpoint-to-endpoint snapping only
  • Snap tolerance (m): Maximum endpoint snap distance in meters (default 5). Geographic CRS inputs are evaluated in a local meter-based projection for this step. If both short-line removal and snapping are enabled, effective tolerance is max(snap_tolerance, minimum_line_length).
  • Group lines: Enable line grouping
  • Merge by group: Merge grouped lines (ignored when Group lines is off)
  • Densify long lines: Insert equalized internal vertices on long lines
  • Max segment length (m): Maximum segment length for densification (default 500)

Tips

  • Input vector and CHM raster should use the same CRS.
  • Works with line data (not points or polygons).
  • If clipping removes all lines, the output may be empty.
  • CHM footprint is generated from raster valid-data cells at raster resolution, so edge boundaries are approximate and can be less accurate.
  • After clipping, visually inspect edge segments and verify that clipped seed lines still match expected line extents.
  • Optional numeric parameters remain visible in the GUI; toggle logic is enforced in backend processing.
  • If CHM footprint shrink is too large, processing fails with guidance to reduce the shrink distance.

CHM footprint shrink distance guide

  • Start with a shrink distance near 1x to 2x CHM pixel size (for example, with 1 m CHM use 1-2 m; with 5 m CHM use 5-10 m).
  • Increase shrink distance when noisy raster edges keep creating false edge segments.
  • Decrease shrink distance when valid lines near canopy boundaries are being clipped too aggressively.
  • For high-resolution CHM, prefer smaller values (0.5-5 m) and adjust gradually.
  • For coarser CHM, larger values may be needed, but always verify edge areas visually in the output.