Octo for cartographic quality

The class comes from the math. The signature belongs to whoever is accountable.

Assessing a product by the PEC means comparing it with more accurate points: 90% of errors below the maximum error and the RMSE below the standard error. The hard part is everything else: building the sample the way ET-CQDG requires, not mixing reference frames, checking point by point and reporting the way the contract asks. Octo draws the sample, does the math, flags what looks wrong and generates the report and the metadata. Classifying the product and signing stay with the technical lead.

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Decree 89.8171984PEC at 90%: 1.6449 × SE

ET-CQDG (DSG)20161st edition, Ordinance 009-DCT

PEC-PCD class A0.28 mmat map scale, versus 0.5 mm in the decree

Sources14listed at the end of the page

What Octo does in quality assessment.

Six possible deliverables, drawn from the research. All work on the delivered product in read-only mode, and all become drafts for the technical lead to check and sign.

Sampling by the standard

Cells, one point per valid cell, sample size from Tables 46 and 47 of ET-CQDG and a draw with a recorded seed, so any auditor can redo it.

Deliverable: list of points to measure in the field

PEC-PCD classification

Errors, RMSE and the two ET-CQDG tests: 90% below the maximum error and RMSE below the standard error, with the class moving down the table when the second one fails.

Deliverable: proposed class, step by step

Batch DEM altimetry

Samples the DEM at the field points with gdallocationinfo, assesses sheet by sheet and flags constant-sign errors, which usually mean a swapped vertical reference.

Deliverable: per-sheet summary with alerts

Logical consistency in SQL

Invalid polygons, overlaps above tolerance and empty mandatory attributes, in a read-only transaction in PostGIS, using the ET-CQDG measures.

Deliverable: percentages and a spreadsheet of cases

Independent report

The four ET-CQDG sections (introduction, products, assessment, summary), with an error map, a per-point table and the date of each procedure, in ODT or PDF.

Deliverable: report ready for review

Metadata with the quality results

ISO 19139 record for each sheet from YAML with pygeometa, with the assessment result in the lineage and the profile chosen by the contracting party.

Deliverable: well-formed XML per sheet

Eight arms, one quality assessment.

The same Octo cycle, applied to cartographic quality control. Each arm has a narrow role; the ones who measure in the field, classify, accept and sign are people.

Discovery
Surveys what was delivered

Scale, product type (CDGV, map sheet, DEM, orthoimage), system, vertical reference, metadata and what the terms of reference require.
Data
Pins down the references

Which table applies (31, 32 or 35), the scale, the ET-EDGV schema, the reference file and the separation between the delivered product and the working copy.
Security
Takes care of access and data

Read access to the delivered dataset, no password in scripts. Cadastral data may contain personal data and products may be restricted: assessed with the client (LGPD) before anything leaves the environment.
Architecture
Picks the path

Isolated lot or lot-by-lot; proposed cell size; script, QGIS plugin or SQL in PostGIS; report format and metadata profile.
Development
Writes the routines

Seeded draw, PAP-PCD calculation, consistency SQL, DEM sampling, report and metadata, with the table and section of the standard noted in each file.
Review
Checks against known cases

Redoes the example from ET-CQDG itself (lot of 190, n = 20) and a case computed by hand. Checks by the numbers and the error map, not by the absence of errors.
Release
Delivers as a draft

Report and metadata go to the technical lead. Nothing is published in an official catalog or sent to the supplier without a person's decision.
Documentation
Records what applies to your project

Tool versions, draw seed, tables used, points checked and each decision by the accountable professional. The assessment of one lot does not apply to another.

Octo works with read access and as support. It does not measure in the field, does not discard points, does not make the final classification and does not sign reports: that belongs to licensed professionals, with an ART when the contract and the professional council require it.

Each task, its own path.

The criteria Octo uses to choose. Always with the version of the standard and of the tools recorded in the report.

Task	Path	Note
PEC-PCD class of a vector dataset	`avalia_pec_pcd.py` with Table 31 or 32	The RMSE-versus-SE step often changes the class
Topographic map class	Same calculation with Table 35	Decree values, classes A to C
Sample size	Tables 46 and 47 (isolated lot) or 44 and 45 (lot-by-lot)	For positional accuracy, as if the LQL were 4%
Sample the DEM at the points	`gdallocationinfo -geoloc -valonly -E -r bilinear`	`-r` requires GDAL 3.10 or newer
Pair product and reference	`qgis_process run native:joinbynearest`	Check only; the matching point is marked by a person
Invalid geometry and overlap	`ST_IsValid` and `ST_Overlaps` in PostGIS	Read-only transaction; fixes on a copy
Interactive assessment	GeoPEC or QPEC plugins in QGIS	Check compatibility with the installed QGIS
ISO 19139 metadata	`pygeometa metadata generate ... --schema=iso19139`	MGB 2009 or 2.0 profile, as the contracting party requires
Independent report	ODT or PDF in the four ET-CQDG sections (5.2)	Signed by the technical lead

From a one-off spreadsheet to acceptance with a trail.

Three steps. Each one only makes sense after the previous one has shown results on your quality control team.

A proposal, not a promise

1 Today

Verifiable calculation

Octo redoes the classification of an assessment the team has already done, with the ET-CQDG steps in plain view.

Horizontal and vertical PAP-PCD with the right table
List of points above the maximum error for checking
Comparison with the team's spreadsheet

Benefit: the same rule in every assessment

2 Next

Sample and lot

Sampling now comes from the script, with a recorded seed, and the DEM and logical consistency checks run in batch.

Draw from Tables 46 and 47
Altimetry per sheet with a reference alert
Logical consistency SQL per class

Benefit: the team reviews one summary, not twelve spreadsheets

3 Later

Acceptance with report and metadata

Each lot closes with an independent report, metadata per sheet and a trail of the accountable professional's decisions.

Report in the four ET-CQDG sections
ISO 19139 XML per sheet
Log of version, seed, tables and decisions

Benefit: the acceptance can be audited later

Confirmed by sources.

Every point below has a source published by the responsible body (Planalto, IBGE, the Brazilian Army, CONCAR), by the project or by the standards organization. The sources are in the next section.

points with a published source, each with its reference alongside.

ConfirmedPEC is 1.6449 × SE, at 90%: Article 8 of Decree 89.817/1984 defines the PEC at 90% probability, with PEC = 1.6449 × SE and standard error, standard deviation and RMSE treated as equivalent; article 9 gives classes A (0.5 mm), B (0.8 mm) and C (1.0 mm).Source: Decree 89.817/1984 (planalto.gov.br)
ConfirmedThe two PAP-PCD tests: ET-CQDG places the product in the class where at least 90% of the points fall below the maximum error and then requires the RMSE to be below the standard error, moving down the table if needed. Control points must be at least three times more accurate than the product.Source: ET-CQDG, 1st ed., Tables 21 and 22 (geoportal.eb.mil.br)
ConfirmedPEC-PCD class A is new: In the ET-CQDG tables, CDGV class A (0.28 mm at map scale) is stricter than the decree's, and the decree's class A value at 1:25,000 (12.5 m) appears as CDGV class B.Source: ET-CQDG, Tables 31 and 35
ConfirmedSample: one point per valid cell: One point per cell with an identifiable feature, ISO 2859 plans and, for positional accuracy, a sample "as if the LQL were 4%". Example from the standard: isolated lot of 190, n = 20.Source: ET-CQDG, sections 4.2 to 4.7 and Annex A

What Octo does and what stays with you.

Octo prepares everything, but does not sign. The document of record stays with whoever is accountable for it.

Octo prepares

Surveys, calculates, organizes and produces the documents: spreadsheets, reports, sheets, maps and drafts.

Deliverable: material ready to check

Your team checks

The licensed professional checks what Octo delivered before signing. If something doesn't add up, it goes back to Octo with the correction.

Step: review by the signer

Who signs

Octo does not sign. Designs, technical reports, ART/RRT (Brazil's professional responsibility records), accountability reports and any official document are still signed by the company's or agency's licensed professional: here, the cartographic engineer or another licensed professional, with an ART; official data goes into the INDE only after approval by the competent authority.

Sign-off: licensed professional, with ART

Sources.

Legislation, standards and documentation used in the research, accessed on October 31, 2026. Paid standards (ISO, ABNT) are only cited, with a link to the official catalog.

Decree 89.817/1984PEC and map classes
ET-CQDG, 1st edition (DSG, 2016)Measures, sampling, PEC-PCD and report
ISO 19157-1:2023Geographic data quality (catalog)
ISO 19157-3Register of data quality measures (draft)
IBGE: MGB profileBrazilian geospatial metadata
FGDC-STD-007.3-1998 (NSSDA)For comparison: 20 points, 95%
QGIS: qgis_processProcessing without the interface
QGIS: Join attributes by nearestnative:joinbynearest
QGIS: release calendar4.2.3 and LTR 3.44.15
GDAL: gdallocationinfoSample a raster at points
GeoPEC pluginPositional accuracy in QGIS
QPEC pluginPAP of point features
pygeometaISO 19139 metadata from YAML
PostGIS: referenceST_IsValid, ST_Overlaps

Your next acceptance, with the math in plain view.

The assessment starts with an evaluation your team has already done, without touching the delivered product. You get the same classification redone step by step, what would change with the ET-CQDG sample and a proposal for what can be automated, and decide with it in hand.

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