feat: add COG writer with Perlin noise pixel generation#99
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- Add noise module: 2D Perlin noise generator (deterministic, spatially correlated) for realistic satellite imagery compression ratios - Add cog module: GDAL-based COG writer using MEM→COG create_copy workflow, gated behind 'cog-writer' feature flag - Single-band UInt8, ZSTD compressed, 256x256 internal tiling - Per-footprint UTM CRS, geotransform from footprint origin - Seed from (footprint_id, cog_id) ensures deterministic output - 24 tests passing (5 noise + 3 COG roundtrip/determinism tests)
- Hoist loop-invariant frequency/dimension divisions in generate_raster - Add generate_raster_into(&mut Vec<u8>) for buffer reuse across COGs - CogConfig now wraps FootprintConfig to eliminate duplicated dimensions - Add pixel readback assertion to roundtrip test (verifies non-trivial data) - Scope band borrow explicitly to clarify lifetime before create_copy
- All noise arithmetic now uses f32 (~2x throughput on ARM NEON) - Row-level y-axis values (grid cell, fractional offset, fade curve) are computed once per row and reused across all 1830 columns - Permutation lookups for p[xi] and p[xi+1] hoisted out of hash step - f32 precision is more than sufficient for UInt8 pixel output
- Add NUM_THREADS=ALL_CPUS to COG creation options - GDAL time per COG: 41.5ms → 15.8ms (2.6x faster) - Total: 54.6ms → 29.2ms per COG (1.87x end-to-end) - Add bench_cog example for profiling noise + COG write
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Summary
cog-writerfeature flag using MEM→COGcreate_copyworkflowStacked on
Test plan
cargo clippy -- -D warningscleancargo fmt --checkclean