# Spatial prior + OSSL spectra pipeline (Modules 3 & 4)

Modules 3 and 4 sit alongside the deterministic key, never inside it:

- Module 3 (`spatial-*`) – pulls a probabilistic prior over RSGs from a regional or global map (SoilGrids, an Embrapa pedological map, or any raster the user supplies) and runs a consistency check that warns when the deterministic classification disagrees with the prior. The key is never overwritten – the prior is purely advisory.
- Module 4 (`spectra-*`, `vlm-*`) – gap-fills horizon attributes (clay, CEC, BS, OC, pH, …) from Vis-NIR / SWIR or MIR spectra via the OSSL library. Predicted values are recorded with `source = "predicted_spectra"` so the evidence grade tracks the substitution.

This vignette walks both modules end-to-end on the canonical Ferralsol fixture, with all external dependencies (raster files, OSSL parquet libraries, ellmer chats) replaced by inline synthetic objects so the example is fully reproducible.

# 1. Start from a partially-described pedon

Take the canonical Latossolo and intentionally erase the CEC and base-saturation values from the lower horizons. We will fill them back in with simulated OSSL predictions in §3.

    pr_full   <- make_ferralsol_canonical()
    pr_partial <- pr_full$clone(deep = TRUE)
    pr_partial$horizons[3:5, c("cec_cmol", "bs_pct") := NA]

    pr_partial$horizons[, .(top_cm, bottom_cm, designation,
                            clay_pct, cec_cmol, bs_pct, oc_pct)]
    #>    top_cm bottom_cm designation clay_pct cec_cmol bs_pct oc_pct
    #>     <num>     <num>      <char>    <num>    <num>  <num>  <num>
    #> 1:      0        15           A       50      8.0     24    2.0
    #> 2:     15        35          AB       52      6.5     17    1.2
    #> 3:     35        65          BA       55       NA     NA    0.6
    #> 4:     65       130         Bw1       60       NA     NA    0.3
    #> 5:    130       200         Bw2       60       NA     NA    0.2

The classification on this incomplete pedon already differs:

    res_partial <- classify_wrb2022(pr_partial, on_missing = "silent")
    res_partial$rsg_or_order
    #> [1] "Nitisols"
    res_partial$evidence_grade
    #> [1] "A"

The evidence grade reflects the missing data – the per-RSG trace records which RSGs returned NA because of attributes we erased.

# 2. Module 3 – spatial prior consistency check

The prior is a probability vector over RSGs from any source – a regional SoilGrids extract, a national Embrapa map, an interpolated kriging surface, etc. For this vignette we build it inline so the example runs without network access:

    # Synthetic prior consistent with the gneiss-Mata-Atlantica context:
    # Ferralsols dominate, with a tail of Acrisols and Cambisols.
    prior <- data.table::data.table(
      rsg_code    = c("FR", "AC", "CM", "AL"),
      probability = c(0.62, 0.20, 0.12, 0.06)
    )
    prior
    #>    rsg_code probability
    #>      <char>       <num>
    #> 1:       FR        0.62
    #> 2:       AC        0.20
    #> 3:       CM        0.12
    #> 4:       AL        0.06

`prior_consistency_check()` confirms the deterministic call (`FR`) is supported by the prior:

    chk <- prior_consistency_check(rsg_code = "FR", prior = prior, threshold = 0.05)
    chk
    #> $consistent
    #> [1] TRUE
    #>
    #> $p
    #> [1] 0.62
    #>
    #> $threshold
    #> [1] 0.05
    #>
    #> $status
    #> [1] "consistent"
    #>
    #> $note
    #> [1] "Assigned RSG 'FR' has prior probability 0.620 at this location (>= threshold 0.050)."
    #>
    #> $top_prior
    #>    rsg_code probability
    #>      <char>       <num>
    #> 1:       FR        0.62
    #> 2:       AC        0.20
    #> 3:       CM        0.12

Now suppose the deterministic key had instead landed on Cambisols. The same prior would flag the disagreement (Cambisols at probability 0.12 vs the dominant Ferralsols at 0.62 – the inconsistency margin):

    prior_consistency_check(rsg_code = "AL", prior = prior, threshold = 0.05)
    #> $consistent
    #> [1] TRUE
    #>
    #> $p
    #> [1] 0.06
    #>
    #> $threshold
    #> [1] 0.05
    #>
    #> $status
    #> [1] "consistent"
    #>
    #> $note
    #> [1] "Assigned RSG 'AL' has prior probability 0.060 at this location (>= threshold 0.050)."
    #>
    #> $top_prior
    #>    rsg_code probability
    #>      <char>       <num>
    #> 1:       FR        0.62
    #> 2:       AC        0.20
    #> 3:       CM        0.12

The deterministic key is never overwritten by the prior. The check only flags cases where a manual review is warranted; the user remains in charge of the final assignment. Real production runs would source the prior from `spatial_prior_soilgrids()` (a live SoilGrids-WCS request) or `spatial_prior_embrapa()`:

    prior <- spatial_prior_soilgrids(pr_partial, buffer_m = 250)

# 3. Module 4 – OSSL gap-filling

The OSSL workflow is:

1. Pre-process the raw spectra (SNV / Savitzky-Golay 1st derivative).
2. Send each horizon’s spectrum through one of three predictors:
   - `predict_ossl_mbl()` – memory-based learning (recommended);
   - `predict_ossl_plsr_local()` – partial-least-squares with a local subset;
   - `predict_ossl_pretrained()` – a pre-trained Cubist or RF model.
3. Convert each property’s prediction-interval width to an A–D confidence grade via `pi_to_confidence()`.
4. `fill_from_spectra()` writes each predicted value into the horizons table AND adds a provenance entry with `source = "predicted_spectra"`.

A production call would look like this (skipped in this vignette because OSSL is a multi-GB dataset that would have to be downloaded):

    fill_from_spectra(
      pr_partial,
      library     = "ossl",
      region      = "south_america",
      properties  = c("clay_pct", "cec_cmol", "bs_pct", "oc_pct"),
      method      = "mbl",
      preprocess  = "snv+sg1",
      k_neighbors = 100L,
      ossl_library = "/path/to/ossl-soilsite-vnir.parquet"
    )

For the vignette, simulate the predicted values directly through `pedon$add_measurement()`:

    preds <- list(
      list(idx = 3, attribute = "cec_cmol", value = 5.5, confidence = 0.78),
      list(idx = 3, attribute = "bs_pct",   value = 14,  confidence = 0.72),
      list(idx = 4, attribute = "cec_cmol", value = 4.9, confidence = 0.79),
      list(idx = 4, attribute = "bs_pct",   value = 13,  confidence = 0.74),
      list(idx = 5, attribute = "cec_cmol", value = 4.7, confidence = 0.70),
      list(idx = 5, attribute = "bs_pct",   value = 13,  confidence = 0.71)
    )

    pr_filled <- pr_partial$clone(deep = TRUE)
    for (p in preds) {
      pr_filled$add_measurement(
        horizon_idx = p$idx,
        attribute   = p$attribute,
        value       = p$value,
        source      = "predicted_spectra",
        confidence  = p$confidence,
        overwrite   = TRUE
      )
    }

    pr_filled$horizons[, .(top_cm, bottom_cm, cec_cmol, bs_pct)]
    #>    top_cm bottom_cm cec_cmol bs_pct
    #>     <num>     <num>    <num>  <num>
    #> 1:      0        15      8.0     24
    #> 2:     15        35      6.5     17
    #> 3:     35        65      5.5     14
    #> 4:     65       130      4.9     13
    #> 5:    130       200      4.7     13

The predicted values are now in the horizons table, and the provenance log records each as `predicted_spectra`:

    prov <- pr_filled$provenance
    prov[source == "predicted_spectra", .(horizon_idx, attribute, source, confidence)]
    #>    horizon_idx attribute            source confidence
    #>          <int>    <char>            <char>      <num>
    #> 1:           3  cec_cmol predicted_spectra       0.78
    #> 2:           3    bs_pct predicted_spectra       0.72
    #> 3:           4  cec_cmol predicted_spectra       0.79
    #> 4:           4    bs_pct predicted_spectra       0.74
    #> 5:           5  cec_cmol predicted_spectra       0.70
    #> 6:           5    bs_pct predicted_spectra       0.71

# 4. Re-classify with the gap-filled pedon

After OSSL fills the missing CEC/BS, the deterministic key has a complete dataset and the classification’s evidence grade reflects the predicted source.

    res_filled <- classify_wrb2022(pr_filled, on_missing = "silent")
    res_filled$rsg_or_order
    #> [1] "Ferralsols"
    res_filled$evidence_grade
    #> [1] "B"
    res_filled$name
    #> [1] "Geric Ferric Rhodic Chromic Ferralsol (Clayic, Humic, Dystric, Ochric, Rubic)"

The evidence grade ladder for the same profile across the three workflows:

Workflow | Evidence grade
--- | ---
Lab-only (full canonical fixture) | A
Spectra-filled (OSSL `predicted_spectra`) | B
VLM-extracted only | C
User-assumed | D

# 5. Combining priors and posteriors

`combine_priors()` merges multiple sources (SoilGrids + Embrapa + a custom map) with weights, returning a single normalised prior that you can feed into `prior_consistency_check()`:

    combined <- combine_priors(
      priors = list(
        soilgrids = data.table::data.table(rsg_code = c("FR", "AC", "CM"),
                                              probability = c(0.62, 0.20, 0.18)),
        embrapa   = data.table::data.table(rsg_code = c("FR", "AC", "NT"),
                                              probability = c(0.55, 0.30, 0.15))
      ),
      weights = c(soilgrids = 0.6, embrapa = 0.4)
    )
    combined
    #>    rsg_code  probability
    #>      <char>        <num>
    #> 1:       FR 0.7139748011
    #> 2:       AC 0.2841641547
    #> 3:       CM 0.0017189621
    #> 4:       NT 0.0001420821

`posterior_classify()` would then take a `ClassificationResult` and a prior, returning a posterior probability over RSGs (the deterministic key contributes a sharply peaked likelihood). Used for ranking ambiguous fixtures or for active-learning loops.

# Summary

- The deterministic key always runs first and is never overwritten.
- Module 3 gives a probabilistic sanity check against external maps and warns on disagreement.
- Module 4 fills missing horizon attributes from spectra, with full provenance, so the evidence grade tracks the substitution.
- Putting them together, you can take a partially-described pedon, fill its gaps from spectra, classify it deterministically, and cross-check the result against a global map – all in one pipeline.

The next vignette (`v06_wosis_benchmark`) shows how to run this whole stack at scale against the WoSIS global pedon archive for paper-grade validation.