Nv Header Structure Interpretation

nv-header-structure-interpretation

Summary

Parse and validate the binary header structure of NV (NMRViewJ) format files, extracting magic number, version, dimensionality, and per-dimension metadata (size, blockSize, frequency, phase, labels). This skill is essential for correctly reading NMR spectroscopy data files and detecting endianness mismatches early in the pipeline.

When to use

You have a raw NV file from NMRViewJ or compatible NMR acquisition software and need to extract header metadata before processing spectroscopic data. Specifically: the file is binary (not text), you do not yet know the endianness or dimensionality, or you need to validate file integrity before attempting block-level data extraction.

When NOT to use

• Input is already a text-based format (e.g., ASCII NMR data, CSV export) — use direct text parsing instead.
• Header has already been extracted and validated in a prior pipeline stage — reuse the cached JSON header.
• File is corrupted or truncated below 2048 bytes — early failure is appropriate; do not attempt recovery here.

Inputs

• binary NV file (first 2048 bytes minimum)
• file path or file handle to NV-format spectroscopy data

Outputs

• parsed header object (JSON-serializable dictionary or file)
• endianness flag (big-endian or little-endian)
• dimension metadata array (size, blockSize, nBlocks, frequency, phase, labels per dimension)
• validation status (pass/fail with diagnostic message)

How to apply

Read the first 2048 bytes of the input NV file using a binary reader (RandomAccessFile or equivalent). Extract bytes 0–3 and validate the magic integer against the expected value 874032077; if validation fails, test little-endian encoding and set an endianness flag. Parse file-level header fields (bytes 4–28) as integers: version, fileHeaderSize, blockHeaderSize, blockElements, and nDim. For each dimension (0 to nDim−1), read the 128-byte dimension section starting at offset 1024 + dim×128, extracting size, blockSize, nBlocks, spectrometer frequency (sf), sweep width (sw), reference point (refpt), reference value (refval), reference units (refunits), a 16-character label string, and phase and domain flags (complex, freqdomain, ph0, ph1, vsize). Validate consistency: confirm that fileHeaderSize matches the declared header size and that blockElements aligns with the product of per-dimension blockSizes. Serialize the complete parsed header object (magic, version, nDim, all dimension metadata, detected endianness) to a JSON output file for downstream stages.

Related tools

• NMRFx (NMR data processing suite that defines and uses the NV file format; provides reference implementation for header parsing and block-level data I/O) — https://github.com/nanalysis/nmrfx

Evaluation signals

• Magic integer matches 874032077 (or correct byte-swapped value after endianness detection)
• fileHeaderSize field equals 2048 (or stated alternative); blockHeaderSize and blockElements are positive integers consistent with dimension declarations
• All nDim dimension sections (0 to nDim−1) parse without out-of-bounds reads; each label is ≤16 characters; size, blockSize, nBlocks are positive
• Consistency check passes: product of per-dimension blockSizes equals declared blockElements
• JSON output is schema-valid and round-trips (re-parsing the JSON yields identical field values)
• Endianness detection is unambiguous: either big-endian OR little-endian yields a valid magic number; conflicts indicate corruption

Limitations

• Magic integer validation assumes the file conforms to NMRViewJ spec; non-standard or corrupted headers will fail early with no recovery path.
• Endianness is detected heuristically via magic-number byte-swap; ambiguous endianness (neither order yields a recognized magic) will cause parsing to halt.
• Dimension metadata is assumed to fit exactly in 128-byte sections at offset 1024 + dim×128; files with non-standard padding or layout will misparse.
• No support for NV format extensions or vendor-specific variants; only the documented fixed-size 2048-byte header and standard dimension fields are parsed.

Evidence

• [other] Extract and validate the magic integer (bytes 0–3) against the expected value 874032077; if mismatch, test little-endian encoding and set endianness flag accordingly.: "Extract and validate the magic integer (bytes 0–3) against the expected value 874032077; if mismatch, test little-endian encoding"
• [other] Read the first 2048 bytes from the input NV file using RandomAccessFile or equivalent binary reader.: "Read the first 2048 bytes from the input NV file using RandomAccessFile or equivalent binary reader"
• [other] For each of nDim dimensions (0 to 7), read the 128-byte dimension section starting at offset 1024 + dim128, extracting: size, blockSize, nBlocks, spectrometer frequency (sf), sweep width (sw), reference point (refpt), reference value (refval), reference units (refunits), label (16-char string), complex flag, freqdomain flag, zero-order phase (ph0), first-order phase (ph1), and vsize.: "For each of nDim dimensions (0 to 7), read the 128-byte dimension section starting at offset 1024 + dim128"
• [other] Validate consistency: confirm fileHeaderSize matches declared size and blockElements aligns with product of per-dimension blockSizes.: "Validate consistency: confirm fileHeaderSize matches declared size and blockElements aligns with product of per-dimension blockSizes"
• [abstract] NMRFx is referenced as the tool for NMR processing and NV file format handling.: "github.com/nanalysis/nmrfx"