Octo for projections and geodesy
Since February 25, 2015, only SIRGAS 2000 is valid in Brazil, and converting legacy data, GNSS point heights and projection choice can all run in batch with PROJ, GDAL, QGIS and pyproj. Octo inventories the collection, lists the possible operations, forces the best one, checks against checkpoints and measures area and scale instead of assuming. Source realization, tolerance and the signed product stay with licensed professionals.
Six possible deliverables, drawn from the research. All work on a copy, with the PROJ and EPSG database versions recorded, and all go to review by whoever is accountable for the product.
Reads the declared system of each layer with ogrinfo -json and gdalinfo -json, identifies the EPSG code and separates what is already SIRGAS 2000, what is SAD69 or Córrego Alegre, what is WGS 84 and what has no CRS.
Converts SAD69, SAD69(96) and Córrego Alegre with IBGE's grids distributed on the PROJ CDN, forcing the best operation and failing when the grid is missing, instead of falling back to an approximation.
Deliverable: converted copy + log + checkWhen the accountable professional pins the method, it carries the same operation to ogr2ogr -ct, to the OPERATION parameter of qgis_process, to ST_TransformPipeline in PostGIS and to pyproj's Transformer.
Computes HN = h − η with the hgeoHNOR2020 grids, choosing the grid by polygon (Imbituba, Santana, western strip), and compares with IBGE's official service and nearby benchmarks (RN).
Deliverable: table per point with uncertainty and differenceMeasures area, scale and convergence in UTM, Albers (EPSG:10857) and Polyconic with Proj.get_factors and compares with the geodesic area, so whoever decides can see the effect of each option in numbers.
Compares PROJ, EPSG database and grid versions across workstations and the server, because 9.8.1 rolled the EPSG database back from v12.049 to v12.029 and two machines may convert differently.
Deliverable: version and difference chartThe same Octo cycle, applied to reference systems. Each arm has a narrow role; the ones who decide the realization, accept the tolerance and sign the product are people.
PROJ, GDAL, QGIS, PostGIS and EPSG database versions on each machine, installed grids and the declared CRS of each file in the collection.
CRS of each layer, source realization, height type (ellipsoidal, normal, inherited) and the field where the height lives.
Official collection read-only; separate working copies. Cadastral data with personal information stays in the client's environment and is assessed (LGPD) before going to any external service.
ogr2ogr or qgis_process; automatic operation with ONLY_BEST or a pinned pipeline; local grid or CDN; local computation checked against the IBGE service.
Python and shell with a log, a trial mode, an explicit failure when the grid is missing and the source of each syntax noted in the file.
Independent checkpoints, IBGE's official service and nearby benchmarks. No errors is not the same as checked.
Only with your OK, it delivers the converted copy and the report. Replacing the official collection is done by a person.
PROJ and EPSG database versions, operation used, grid and SHA-256, accepted tolerance and who accepted it. A choice made for one project does not automatically apply to another.
Octo works with read access and as support. It does not decide the realization, does not set tolerances, does not sign products and does not replace ProGriD or the IBGE service as the official reference.
The criteria Octo uses to choose, with the documentation for the installed version.
| Task | Path | Note |
|---|---|---|
| Know what's in the collection | ogrinfo -json -so, gdalinfo -json, projinfo --identify | Nothing is changed |
| List operations and accuracy | projinfo -s A -t B --summary | --spatial-test intersects and --area change the list |
| Download only the grid you need | projsync --file br_ibge_SAD69_003.tif | Or PROJ_NETWORK=ON; on a closed network, copy the grid |
| Transform points | cs2cs --only-best --no-ballpark | Error if the grid for the best operation is missing |
| Transform vectors | ogr2ogr -ct_opt ONLY_BEST=YES or -ct with a pipeline | -ct_opt since GDAL 3.11 |
| Reproject in QGIS in batch | qgis_process run native:reprojectlayer with OPERATION | Overrides the project setting for that layer |
| Reproject in the database | ST_Transform; ST_TransformPipeline to pin the method | Check the PROJ version linked to PostGIS |
| Normal height | hgeoHNOR2020 grids + IBGE service | Not on the PROJ CDN |
| Height included in the transformation | 3D CRS on both sides (cs2cs --3d) | Since PROJ 9.1, without 3D on both sides the height doesn't change |
| Measure distortion | pyproj.Proj.get_factors + Geod | Geodesic area as the reference |
Three steps. Each one only makes sense after the previous one has shown results on your team.
A proposal, not a promise
Octo shows what's in the collection and how each machine converts, without changing anything.
Conversions with the best operation, checked against checkpoints, and normal heights checked against the official service.
Approved operations become pinned pipelines, the same in QGIS, the database and the scripts.
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.
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points with a published source, each with its reference alongside.
Octo prepares everything, but does not sign. The document of record stays with whoever is accountable for it.
Surveys, calculates, organizes and produces the documents: spreadsheets, reports, sheets, maps and drafts.
Deliverable: material ready to checkThe 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 signerOcto 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 ARTDocuments from IBGE, SIRGAS and the PROJ, GDAL, QGIS, pyproj, geopandas and PostGIS projects used in the research, accessed on October 31, 2026.
The assessment starts with an inventory of the collection and a chart of the versions each machine uses, without changing anything. You get the list of what to convert, of the questions only your team can answer and of how to check, and decide with it in hand.
