Alignment#
Work in progress
Placeholder content. Being rewritten with figures.
After bundle adjustment + stereo + DEM generation, residual bias remains relative to true ground; pc_align registers the DEM to a trusted reference using ICP.
The reference dataset#
ICESat-2 ATL06-SR for Earth, MOLA for Mars, LOLA for the Moon, or any prior high-quality DEM (3DEP, ArcticDEM, regional lidar).
What pc_align does#
ICP iteratively finds the rigid transformation (translation, optional rotation, optional scale) that minimizes nearest-neighbour distances between the source point cloud (your DEM) and the reference.
When pc_align helps and when it doesn’t#
It helps with near-uniform bias and small global tilt; it doesn’t help with localized blunders or non-rigid deformation, which need fixing upstream.
Reading the alignment report#
pc_align prints percentile breakdowns of inter-point distances before and after; the median (50th percentile) drop is the headline metric.
The --pc_align flag in asp_plot#
asp_plot --pc_align runs pc_align against the appropriate altimetry reference based on the DEM’s CRS and adds an alignment-summary page to the PDF report.