geozl 0.1.0

Geospatial codec extensions for OpenZL.

Spatial predictors and near lossless quantizers, packaged as OpenZL custom codecs.

OpenZL models compression as a graph of codecs and ships the decode recipe inside every frame, so one universal decoder reads any frame. It compresses 1D streams and has no notion of a 2D raster. geozl adds the spatial codecs for it.

A geozl codec is one node in the OpenZL graph. It transforms the tile, a numeric stream, and carries whatever the decoder needs to invert it in the codec header inside the frame. The full rules live in the specification.

Status

geozl is experimental. The codecs, their parameters, and the codec header layout can change between versions with no migration path. Pin a version for anything you cannot regenerate.

[!WARNING] geozl codecs are not part of OpenZL. They register at runtime and take custom transform ids in the 0x72D700-0x72D7FF block. A frame that uses them decodes only with a reader that has geozl registered, a frame of built-in OpenZL codecs stays portable. Whether any geozl codec lands in OpenZL upstream is undecided.

Install

pip install geozl

You compose the geozl codecs into an openzl.ext graph, they chain like any other node.

import openzl.ext as zl
import geozl

c = zl.Compressor()
g = zl.graphs.Compress()
g = zl.nodes.Zigzag()(c, g)
g = geozl.lossless.PlanarInt(width=512)(c, g)
c.select_starting_graph(g)

Codecs

Two families, both registered as OpenZL custom codecs that chain like any other node.

Near lossless

Quantizers, namespace geozl.lossy. A frame is no longer bit exact, carries one quantizer at the head, and bounds its error by the parameters in the frame. Each declares one error mode. ABS holds a fixed absolute tolerance, the same everywhere, for elevation, depth, coordinates. REL holds a fixed relative tolerance, a percentage of each value, for radiance, reflectance, SAR amplitude.

codec	CTid	mode	error
quant_linear	0x72D780	ABS	every value within max_error
quant_log	0x72D781	REL	every value within rel_error of itself

Lossless

Spatial predictors, namespace geozl.lossless. Each rewrites a tile as residuals against decoded neighbours, bit exact. They are reversible and domain agnostic, so these are the candidates to merge into OpenZL upstream.

codec	CTid	what it does
delta_w	0x72D701	horizontal delta
delta_n	0x72D702	vertical delta
planar	0x72D703	predicts each pixel from W plus N minus NW

License

BSD-3-Clause

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