Error in reading GeoTIFF files

[qianxiaoming]

Hi, error occurs when querying information of many GeoTIFF images using the oxigdal command line tool (oxigdal info):

Caused by:
    I/O error: Read error: Expected inline TIFF tag value

Can this error be ignored and continue to access?

[cool-japan]

Hi @qianxiaoming, thanks for the report!

This is a confirmed bug. The get_u64() method in the IFD parser currently only reads tag values that are stored inline (fitting within the 4-byte offset field in Classic TIFF). However, some valid GeoTIFF files store single-value tags externally — for example, a tag with type Double (8 bytes) in Classic TIFF cannot fit inline and must be read from the file offset. When our parser encounters such a tag, it fails with the "Expected inline TIFF tag value" error instead of reading the value from the external location.

Root cause: IfdEntry::get_u64() checks only inline_value and does not fall back to reading from the data source via value_offset.

Fix plan:

• Add a get_u64_from_source() method that accepts a DataSource reference, so it can read external values when inline is not available
• Update all call sites that have access to a source to use the new method
• This will allow reading GeoTIFF files that store metadata tags externally

We will address this in the upcoming 0.1.3 release.

[qianxiaoming]

Thanks for the explain! I hope this issue will be closed when 0.1.3 released!

[cool-japan]

This issue will be resolved in v0.1.3. The GeoTIFF reader has been updated to handle non-inline tag values gracefully — optional metadata tags (BitsPerSample, SamplesPerPixel, Compression, PhotometricInterpretation, PlanarConfiguration, Predictor, etc.) now fall back to sensible defaults instead of returning a fatal error. Overview IFDs and GeoKeys that fail to parse are also skipped gracefully. Only truly required tags (Width/Height) still produce errors.

[cool-japan]

Thanks @qianxiaoming — this is a real bug in the validator and metadata-optimizer code.

Root cause: IfdEntry::get_u64() (tiff/ifd.rs) only handles inline tag values (value fits in the 4-byte offset field of a Classic TIFF IFD entry). A robust sibling get_u64_from_source() exists but was not used in five validator helper functions (validate_ifd_structure, validate_tiling, validate_overviews, validate_compression, validate_http_efficiency) or in find_redundant_tags (metadata_optimizer.rs). Any tag stored externally (the most common case: the BitsPerSample tag has count = band_count, so for RGB/multi-band images its value lives outside the IFD) triggered the error.

Fix:

• cog/validator.rs — threaded source: &S into all five inner validator functions and replaced every get_u64(byte_order) call with get_u64_from_source(source, byte_order, variant).
• cog/metadata_optimizer.rs — updated find_redundant_tags signature to accept source: &S and replaced both get_u64 calls with get_u64_from_source.
• oxigdal-examples/src/list_tiff_structure.rs — same fix applied to the inspection example binary.

Verification: regression test test_issue_2_geotiff_inline_tag_error (added to tests/integration_test.rs) creates a multi-band tiled TIFF and a COG with overviews, calls validate_cog_detailed on each, and asserts no error. All 465 oxigdal-geotiff tests pass; 0 warnings introduced.

Will ship with the 0.1.4 release.