Phase 0–1. Verifies the GeoTIFF reader and the terrain-analysis
kernel against analytic surfaces with hand-computable answers, against the
sign conventions the tool's argument depends on, and against the real
Ørndalen LiDAR figures recorded independently in
data/orndalen/SOURCE.txt by a separate Python/tifffile path.
Each row states the convention it is testing, so this table is also the
specification.