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perf(data): the untiled GeoTIFF export takes a predictor and Deflate's fastest level (#1111) - #1886
Second item of step 5 of #1111. The untiled GeoTIFF (share.exportRaster without "cog", and every other caller of geotiff::write/write_all, such as tool outputs and the rasters a project keeps) is now written by the in-house TIFF writer the COG export uses, instead of the tiff crate's encoder. The tiff crate's encoder can't write the floating-point predictor. Its Deflate speed also depended on which flate2 backend another crate happened to turn on.
A single band of a few classes keeps no predictor at Deflate's default level, as the COG does. Six classes stored as Float32 compress to 2.9% of raw that way, against 7.2% with Predictor 3 at level 1.
The samples, their types and the other tags are unchanged: georeferencing, no-data, band names and classes, copyright, and extra samples. The strips are about 1 MB of rows each, as before. The XResolution, YResolution and ResolutionUnit tags (1/1, no unit) are no longer written, as the COG doesn't write them either.
A file that could pass 4 GiB is now written as BigTIFF; the old encoder only wrote classic TIFF.
In the code:cogwrite::write_strips writes one image in strips. It reuses the COG writer's directory layout, table patching and predictors (predict_rows, fill_tables, predictor_of). The georeferencing tags are built once for both writers (geo_entries). geotiff::encode keeps its choice of samples and hands each branch's samples to write_strips. The strips count as progress, and Cancel is checked before each strip and once after the last.
Measured on a 9667 × 11947 Float32 elevation model, exporting it untiled with the release CLI. The base is main's untiled writer, compared with this branch, run alternately three times. Other jobs were loading the machine, so the table gives CPU time (user + system):
main
This branch
share.exportRaster (read and write), CPU s
26.6–27.9
13.4–14.3
Writing alone (less the 6.6 s read), CPU s
about 20.5
about 7
File
376.2 MB
281.9 MB
Peak memory
0.84 GB
0.76 GB
Not in this pull request: the untiled file is still built in memory before it is written (geotiff::write returns the bytes), and strips are compressed on one thread (step 6).
Testing
New test cogwrite::tests::a_cancel_during_the_last_strip_stops_the_untiled_write: a cancel that comes while the last strip is made stops the write.
New test cogwrite::tests::untiled_strips_read_back_exactly_through_their_predictor checks four cases, each over several strips:
a Float32 band with NaN, negative and very large values gets Predictor 3;
8-bit RGB gets Predictor 2;
five float bands through write_all (RGB, alpha and one more) get Predictor 3;
a Float32 band of three classes gets none.
Every value of every band reads back exactly.
The existing GeoTIFF and COG tests pass unchanged (cargo test -p rustgis-data raster::, 224 tests). They cover copyright, no-data, alpha, RGB with near-infrared, multiband write_all, band names and classes.
GDAL reads both files with the same checksum and statistics. gdalinfo differs only in PREDICTOR=3, 27 rows to a strip instead of 26, and the resolution tags left out.
Standard GeoTIFF exports are written in strips, with cancellation checks during export.
TIFF format selection accounts for estimated file size; exports that exceed Classic TIFF limits report an error.
Documentation
Clarified that standard GeoTIFFs use strips, while cloud-optimized GeoTIFFs use 512-pixel tiles, and that both use Deflate compression with predictors.
Explained BigTIFF selection, browser download behavior, and which bands are treated as categorical, including how color and grey-with-alpha files are averaged.
…s fastest level (opengeos#1111)
The untiled GeoTIFF writer (geotiff::write and write_all) writes its strips
through the COG writer's code instead of the tiff crate's encoder, which can't
write the floating-point predictor: floats take Predictor 3, bytes Predictor 2,
a single band of a few classes none at Deflate's default level, everything else
Deflate level 1 through miniz_oxide. The samples and tags are as before, apart
from the resolution tags, which are no longer written. A file that could pass
4 GiB is now BigTIFF instead of an error.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
No actionable comments were generated in the recent review.
Walkthrough
Untiled GeoTIFF export now uses shared TIFF-writing helpers to write compressed row strips. The writer selects sample types and metadata, checks cancellation during strip writing, and handles Classic TIFF size limits. Tests cover multiple sample layouts, and the export documentation describes strip and tile output.
The new writer groups rows into strips, writes compressed strip data, checks cancellation, and handles Classic TIFF size limits. Tests cover float, RGB byte, multiband float, and categorical samples, including cancellation.
GeoTIFF encoding uses the shared strip writer and metadata helpers. The documentation describes strip and tile output, compression, overview selection, and the TIFF size threshold.
sequenceDiagram
participant GeoTIFFEncode
participant Put
participant WriteStrips
participant RowCallback
GeoTIFFEncode->>Put: pass image descriptor and interleaved samples
Put->>WriteStrips: pass strip descriptor and row callback
WriteStrips->>RowCallback: request rows for each strip
RowCallback-->>WriteStrips: return row bytes
WriteStrips-->>Put: write compressed strips and patch tables
Loading
Possibly related issues
opengeos/RustGIS#1111 — The change routes untiled export through predictor handling, addressing the issue’s stated untiled Predictor 3 limitation. The issue also lists other work not covered by this change.
Untiled GeoTIFF export now uses the shared strip writer with cancellation checks and round-trip tests. No concrete merge-blocking defect was found. The only follow-up is to reconcile the PR description with the code, which does report strip progress.
Pre-merge checks: 4
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Title check
The title uses the conventional commit form and names two changes: a predictor and Deflate's fastest level for the untiled GeoTIFF export. The change set matches this. It replaces the tiff crate encod…
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Check skipped because no linked issues were found for this pull request.
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The description follows the repository template. It has Summary, Testing, UI evidence and Related issue sections. The Summary explains what changes, why it changes (the tiff crate encoder cannot write…
Full details: Title check
Explanation
The title uses the conventional commit form and names two changes: a predictor and Deflate's fastest level for the untiled GeoTIFF export. The change set matches this. It replaces the tiff crate encoder with the in-house strip writer, which applies Predictor 3 to floats, Predictor 2 to bytes, and Deflate level 1. The title omits the switch to the in-house writer and the BigTIFF change, but it names a real and central part of the change.
Full details: Description check
Explanation
The description follows the repository template. It has Summary, Testing, UI evidence and Related issue sections. The Summary explains what changes, why it changes (the tiff crate encoder cannot write the floating-point predictor, and Deflate speed depended on the flate2 backend), and how the code is organised. It gives measured CPU time, file size and peak memory for a 9667 × 11947 Float32 model. The Testing section names two new tests, the existing test run (224 tests), GDAL comparison and CI status. The UI evidence section says there is no visible UI change, which matches the template. The Related issue section says 'Part of #1111'. The description is complete and specific.
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A rabbit packs rows, strip by strip, With pixels tucked in a Deflate clip. Predictors guide each sample through, While progress counts the strips anew. TIFF tags settle into place, And carrots wait beside the case.
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The untiled writer's "classes" test differs from the COG's for Float32 bands.few_classes(b) counts any band with 64 or fewer distinct values, Float32 included. The COG's plan() (cogwrite.rs:230) only takes that route when sample != Sample::Float. So a Float32 band with ≤64 values gets predictor 1 at Deflate level 6 here, but predictor 3 at level 1 in cog: true output of the same raster.
This is probably deliberate (the 2.9% vs 7.2% measurement in the PR body points that way), but the doc comments on Strips.classes and write_strips, the PR body ("as the COG does") and data.md ("none for classes") all say the two writers agree. Either add the Sample::Float guard here to match the COG, or keep the behaviour and say in the doc that untiled Float classes take no predictor on purpose. The new test's "a band of three classes gets none" case is a Float32 band, so it locks in this divergence without checking the COG.
Confidence: high that the two writers differ. Medium on whether it is the wrong choice.
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Intended. Both writers send classes to the same compression; what differs is the sample type they store them in. The COG writes a band of whole-number classes as bytes (so its categorical excludes floats, which are a range there), while the untiled writer always writes a single band as Float32, so the same classes reach it as floats. On six classes stored as Float32, no predictor at level 6 gives 2.9% of raw, Predictor 3 at level 1 gives 7.2%, which is why the untiled check doesn't exclude floats. A raster that really is Float32 with 64 or fewer distinct values differs between the two, as you say; that's rare, and either result is correct. Saying this in the Strips.classes doc and data.md is a wording point, left for the release quality pass.
None confirmed. I checked the strip layout, the tag and table patching, the BigTIFF switch, the cancel points, the predictor-per-row handling against whole-row strips, and the test expectations. They hold.
Security
None found. The changes add no input parsing and no new external reads.
Performance
Strips are compressed on one thread. The PR body defers this to step 6, which is acceptable as a stated plan (AGENTS.md says "where practical"). Confidence: high that it is single-threaded, low that it needs to change now.
Quality
Inline comment posted (crates/data/src/raster/geotiff.rs:1712, confidence high on the divergence, medium on whether it is wrong): few_classes also matches Float32 bands with ≤64 distinct values. The COG excludes Float from that path (cogwrite.rs:230). The untiled file therefore gets no predictor at level 6, where the COG gets predictor 3 at level 1. The docs and PR body say the two agree, and the test's "three classes" case is a Float32 band, so it locks the divergence in.
write_strips is pub(super) but is linked from the public write doc (geotiff.rs:1645). This gives a rustdoc private-intra-doc-link warning. Nit, confidence high. CI does not appear to run cargo doc.
write_strips checks for Cancel per strip but counts no progress, although it knows the strip count. progress::step(n) both counts and checks. Pre-existing, but the loop is rewritten here. Confidence: low–medium.
AGENTS.md
Nothing that breaks a rule. The new geo_entries and write_strips do not drop data, and Strips has no silent loss. Two points to note: the progress item above, and the single-threaded strip loop (deferred in the PR body).
I left 0 earlier concerns alone; there were no prior review threads.
Change size
Compared with the base branch (the whole PR, merge base d39c16e to head 6755b8d).
The intra-doc link from the public write doc to the pub(super)write_strips: left for the release quality pass.
Progress: write_strips checks Cancel per strip but deliberately counts nothing. geotiff::write runs inside other commands and tools (Kriging, Kernel Density, tool outputs kept by the project), and progress::begin there would reset the count of the command that called it. The COG writer counts because only an export calls it. The old encoder counted nothing either.
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Actionable comments posted: 2
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @crates/data/src/raster/cogwrite.rs:
- Line 824: In geotiff::write, add a cancellation check after the final strip is
compressed and the tables are patched, immediately before returning success.
This ensures cancellation during the final strip is reported instead of treating
the export as complete.
Review comments at @docs/user-guide/data.md:
- Around line 1189-1190: Qualify the overview description so pixel-based class
selection is promised only for classes that the COG writer treats as
categorical; do not imply that every band with a few whole-number values
receives this behavior. Keep the surrounding overview explanation intact.
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Also say which rasters' overviews take a pixel rather than an average:
a palette, a band with class names, or an 8- or 16-bit band of a few
whole-number values.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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The untiled writer doesn't count its progress, though the strip count is known here. The comment this PR removed from Probed said "the encoder doesn't say where a strip ends", but write_strips now does say it. The COG writer reports its work with progress::begin(tiles) and progress::step(1) (cogwrite.rs:693 and 699). AGENTS.md asks long loops to count their progress when it can be measured, so a desktop export of a large untiled file shows no count. Cancel is still honoured, since step returns Cancelled too.
Suggested change (counts one strip before each is made, same as the COG loop):
Suggested change
for y in(0..img.hasusize).step_by(per_strip asusize){
crate::progress::check()?;
crate::progress::begin(strips asu64);
for y in(0..img.hasusize).step_by(per_strip asusize){
crate::progress::step(1)?;
Confidence: medium-high. The only open choice is whether the caller already began a different total; the COG writer makes the same choice, so this matches it.
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Taken in 83e2bfd (on the PR at 51aac9c). write_strips now calls progress::begin(strips) and progress::step(1) before each strip, the same as the COG loop. The earlier reply said that counting would reset a caller's count, and that was wrong: begin starts the caller's next step, so the write shows as a step of its own. No caller writes a GeoTIFF inside a loop it counts itself. a_cancelled_raster_write_stops now checks that an 1100-row Float32 write counts its 5 strips.
The other points in the review summary (the shadowed line, places.first_mut(), the test doc's width, and a test of the BigTIFF switch) are left for the release quality pass.
None found. I checked the strip layout, predictor 2 and 3 row handling, the classic/BigTIFF choice, table patching, the zero-size and line == 0 guards, the final cancel check (cogwrite.rs:838–839), and the geotiff.rs branch conversions (ExtraSamples, nodata, and the band lists for each branch). Predictor choice is lossless whatever stats.categories says, so stale statistics can cost compression but not data. Confidence: high.
Security
None found in the changed code. Confidence: high.
Performance
None beyond the stated trade-offs. Strips are compressed on one thread, which the PR defers as step 6. Confidence: high.
Quality
Nits, left for the release quality pass:
predict_rows shadows its line parameter inside chunks_exact_mut(line).
write_strips (cogwrite.rs ~833) pushes places through if let Some(p) = places.first_mut(). A plain Vec<(u64, u64)> passed as from_ref would read better.
The doc comment on the new test (cogwrite.rs ~1196) runs past the usual line width.
Confidence: high.
AGENTS.md
Never hold the window: the untiled strip loop calls progress::check() but never begin or step, though the strip count is known. Inline comment posted at cogwrite.rs:823–824. Confidence: medium-high.
Test coverage gap, not a rule breach: no test exercises the BigTIFF branch of write_strips, though the PR says untiled files over 4 GiB are now BigTIFF. Factoring the big decision into a small function would make it testable. Confidence: medium.
Earlier concerns left alone (3 of 3 already raised):
geotiff.rs:1713: the untiled writer's class test includes Float32 bands, unlike the COG. The author's reply explains this as intended, and the reply holds. Left alone.
cogwrite.rs:824: a final cancel check after the last strip. The check is now in the code (cogwrite.rs:838–839), so nothing more to post.
data.md:1190: outdated, and the text no longer makes the claim.
Change size
Compared with the base: merge base e572684 to PR head fcf98f0.
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Untiled writes now reset the progress of a run that calls them.progress::begin is a reset, not an addition: analysis::control::Control::begin sets done back to 0 and replaces total. Before this PR the untiled writer counted nothing, so it never touched a caller's count. Now a tool that counts its own steps and then writes its outputs with geotiff::write loses that count. For example, the Kriging tool (crates/analysis/src/tools.rs ~4469) writes two rasters after its loop, so its progress jumps back to 0 of N strips while the outputs are written.
This is cosmetic: Cancel still works, since step checks the probe. A possible fix is to count the strips without calling begin when a caller already has a total, or to give the untiled path a begin-free variant. The COG writer has the same reset, but it is not called from tools.
Confidence: medium (about 55%). I did not confirm the Kriging run's exact probe setup.
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Intended. A data-crate begin starts the caller's next counted step (analysis::control::begin documents itself as "starts counting a step of total items"), and the progress shows the step under way. When Kriging writes its outputs after its loop, the write appears as a step of its own, counted in strips, rather than a bar that stays full while the files are written. Export Tiles works the same way: it counts its tiles, then the GeoTIFF writer counts its own step. No caller writes a GeoTIFF inside a loop it counts itself, so nothing goes back to zero part-way through a step.
I read the full diff, the three changed files, the prior review threads, and the surrounding code in progress.rs, cogwrite.rs, geotiff.rs, the analysis Control probe, and the callers of geotiff::write. The core change looks correct to me. The strip layout, offsets, predictors, BigTIFF choice, cancel checks and tag ordering all hold up, and the new tests cover the paths they claim to. I found one behaviour regression, which I posted inline, and a few lower-confidence points below.
Bugs
Progress reset during untiled writes (cogwrite.rs:824, inline comment posted). write_strips calls progress::begin(strips). Control::begin resets done to 0, so a tool that counts its own steps and then writes outputs (Kriging writes two rasters after its loop) shows its progress jumping back to 0. Cancel still works. Confidence: medium (about 55%).
Security
None found. The new code takes no external input beyond raster data already in memory, and it adds no unchecked indexing.
Performance
Untiled files are still built whole in memory (put builds the full sample vector, and geotiff::write returns bytes). The PR body says so, and it is out of scope here.
All untiled non-class bands now use Deflate level 1 (previously the tiff crate's Balanced level). The PR measures only a Float32 DEM. Photographic 8-bit RGB exports may come out larger, and the PR doesn't measure that. Confidence: low, since this is a trade-off, not a defect.
Quality
Unchecked strip length (cogwrite.rs, write_strips, around the rows(...) call). predict_rows uses chunks_exact_mut, which silently ignores a partial trailing row. write_strips does not check that raw.len() equals rows × line. Today the only caller is put, which always supplies the exact length, so this is not reachable. It is a hardening point given the "never silent" rule. Confidence: low.
Misleading doc on put (geotiff.rs:1659). It says the strips are written "at the end of out", but write_strips seeks to 0 and requires out to be empty.
Redundant condition (cogwrite.rs:230). !b.classes.is_empty() || is repeated, because few_classes already checks it.
Nits in this group are left for the release quality pass under AGENTS.md.
AGENTS.md
No unwrap, expect, unsafe or panic added to non-test code. Test code uses unwrap, as the existing tests do.
Layering is unchanged, and the code stays inside rustgis-data.
The cancel test and the progress test cover the new strip loop. The untiled path's cancel check is per strip, which the doc comment states.
The docs in data.md match the planner's categorical rule.
Already raised (left alone)
Four earlier threads exist. I did not re-raise any of them:
The Float32 classes predictor divergence (geotiff.rs:1713). The author answered "intended", so I left it alone.
The untiled progress count (cogwrite.rs:824). The earlier thread was addressed by adding begin. My new point about the reset is a different concern, and I posted it inline.
The cancel after the last strip. Resolved and fixed.
The overview wording in data.md. Resolved; the current text matches the planner.
That is 4 earlier concerns left alone, and 1 new inline comment posted.
Change size
Compared with main (merge base e572684 to PR head 51aac9c).
The unchecked strip length (unreachable: put always supplies whole rows), the put doc saying "at the end of out", and the repeated class-name check in plan: left for the release quality pass.
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Summary
Second item of step 5 of #1111. The untiled GeoTIFF (
share.exportRasterwithout"cog", and every other caller ofgeotiff::write/write_all, such as tool outputs and the rasters a project keeps) is now written by the in-house TIFF writer the COG export uses, instead of thetiffcrate's encoder. Thetiffcrate's encoder can't write the floating-point predictor. Its Deflate speed also depended on whichflate2backend another crate happened to turn on.What changes in the file:
In the code:
cogwrite::write_stripswrites one image in strips. It reuses the COG writer's directory layout, table patching and predictors (predict_rows,fill_tables,predictor_of). The georeferencing tags are built once for both writers (geo_entries).geotiff::encodekeeps its choice of samples and hands each branch's samples towrite_strips. The strips count as progress, and Cancel is checked before each strip and once after the last.Measured on a 9667 × 11947 Float32 elevation model, exporting it untiled with the release CLI. The base is main's untiled writer, compared with this branch, run alternately three times. Other jobs were loading the machine, so the table gives CPU time (user + system):
share.exportRaster(read and write), CPU sNot in this pull request: the untiled file is still built in memory before it is written (
geotiff::writereturns the bytes), and strips are compressed on one thread (step 6).Testing
cogwrite::tests::a_cancel_during_the_last_strip_stops_the_untiled_write: a cancel that comes while the last strip is made stops the write.cogwrite::tests::untiled_strips_read_back_exactly_through_their_predictorchecks four cases, each over several strips:write_all(RGB, alpha and one more) get Predictor 3;Every value of every band reads back exactly.
cargo test -p rustgis-data raster::, 224 tests). They cover copyright, no-data, alpha, RGB with near-infrared, multibandwrite_all, band names and classes.gdalinfodiffers only inPREDICTOR=3, 27 rows to a strip instead of 26, and the resolution tags left out.-D warnings, the workspace tests andlayers, wasm, licences) on the fork at 51aac9c (merged with main, after perf(analysis): hillshade is made and written as bytes (#1111) #1887): pass (run)UI evidence
No visible UI change.
Related issue
Part of #1111
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