build_messages_per_message/3 was slicing the wgrib2 -lola bin output as
a packed float32 stream, ignoring the 4-byte record-length header + 4-byte
trailer that Fortran unformatted records prepend/append around each
message's data block. First value of message 0 came back as ~2.24e-44
(little-endian float32 of the int-16 record length), and every subsequent
message was shifted by 8 bytes so values spilled into neighbouring cells.
Fix: propagate the correct offset math already used by parse_lola_binary/3
(record_overhead = 8, stride = bytes_per_message + 8, data_offset =
msg_idx * stride + 4).
Flipped the characterization test from metadata-only to per-cell physical
asserts (200 K < TMP, DPT < 340 K; DPT <= TMP) and a 0.01 K cross-check
against extract_grid/3 output on the same fixture + bbox. Latent bug —
no production callers of extract_grid_messages*.
16 characterization tests against real wgrib2 binary + checked-in HRRR
fixtures: extract_grid/3 (bbox + physical sanity on TMP/DPT + longitude
convention), extract_grid_from_file/3, extract_grid_from_file_mapped/4
reducer plumbing, extract_grid_messages/3 metadata, extract_points_from_file/3
nearest-neighbor snap, undefined-value sentinel filtering, empty-match and
error shapes. Tagged @describetag :slow so they run on 'mix test --include
slow' (project default excludes slow, matches existing HRRR/NARR tests).
Surfaces one real bug (not fixed): extract_grid_messages variants don't
account for the 8-byte Fortran record overhead between messages in wgrib2
-lola output, so per-message values after the first are shifted. The
correct offset math exists in parse_lola_binary/3. Tests characterize
current behavior (metadata-only); worth a follow-up fix + value-range
assertions.
Aliases: add module aliases for 9 nested module references
Apply: replace apply/3 with direct module attribute calls
Line length: break 1 long spec line
Refactoring: extract helpers to reduce complexity and nesting
in show.ex, radio.ex, weather workers, terrain, duct detection,
backfill dashboard, contact map, and mix tasks
Add extract_values/3 to SimplePacking and ComplexPacking for batch
index extraction from a single GRIB2 message. Add extract_grid/2 to
Extractor which takes a list of {lat, lon} points and returns all
variable values for each point, skipping points outside the grid.
This enables extracting weather data for many grid points from a
single HRRR download instead of re-parsing per point.
extract_n_values_array used Enum.take(count) on a reversed list
before reversing it, which included padding values from byte
alignment and dropped actual values. When group count * bits
wasn't a multiple of 8, the extra padding bits produced a
phantom value that shifted the entire array by one position.
This caused cascading errors in spatial differencing — values
started correct but diverged exponentially (DPT decoded as
38 billion K instead of 275 K).
Fix: reverse the list first, then take count, so padding values
at the end are discarded instead of actual values at the start.
Instead of returning "malformed section" on trailing bytes or truncated
sections, attempt to return parsed results. This handles older HRRR
files (2019) that have padding bytes after the last section.
Eliminates the external wgrib2 C tool dependency that blocked HRRR
processing. Implements Lambert Conformal projection, simple packing
(Template 5.0), complex packing with spatial differencing (Template 5.3),
and GRIB2 section parsing — enough to extract point values from HRRR
grid data using only Elixir.
