OS Pillar Trigpoint Import
OS Pillar Trigpoint Import is an import of a subset of the Ordnace Survey (OS) triangulation station dataset. The original data is supplied as a CSV file covering Great Britain. The import focusses on all the (valid, non-destroyed) pillars in the OS dataset that are currently not in the OSM dataset.
Goals
Currently OSM has upto 1/3rd of the UK pillars present as nodes, but in reality this appears to be significantly less, as the nodes under the grouping man_made=survey_point are myriad and inconsistent.
The goal is to take the best available open data source (from the OS), and import as many pillars into OSM that is practicable whilst handling any conflation.
Schedule
The first evaluation happened back in 2016.
A new evaluation was started around the end of May 2026.
The topic was raised on the Talk-GB mailing list 2026-06-09.
Discussion is on-going. Ideally the import will conclude during 2026.
Import Data
Background
The following data sources are used:
- Ordnance Survey triangulation stations CSV: https://www.ordnancesurvey.co.uk/geodesy-positioning/legacy-data/trig-search
- Data license: https://www.nationalarchives.gov.uk/information-management/re-using-public-sector-information/uk-government-licensing-framework/open-government-licence/
- Type of license: OGL-UK-3.0
- Link to permission From 2016: https://www.nationalarchives.gov.uk/information-management/re-using-public-sector-information/uk-government-licensing-framework/open-government-licence/
- OSM attribution (if required): From the OGL license page:
- The OGL requires you to attribute the information provider and source of the information. This is already handled on the generic OSM copyright page
- ODbL Compliance verified: Confirmed with OSM LWG via email on 2026-07-13, Ticket#2026062410000538
- Ordnance Survey benchmarks CSV: https://www.ordnancesurvey.co.uk/geodesy-positioning/legacy-data/benchmark-search
- Data license: https://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/
- Type of license: OGL-UK-3.0
- Link to permission: Implicit from OGL-UK-3.0
- OSM attribution: Yes
- The OGL requires you to attribute the information provider and source of the information. This is already handled on the generic OSM copyright page
- ODbL Compliance verified: Confirmed with OSM LWG via email on 2026-07-13, Ticket#2026062410000538
OSM Data Files
OSM datafiles, in the form of OSC XML change files, are provided on the github repository.
Import Type
The primary import of all missing pillars that have no conflation should be a one time import. The UK trigpoints are no longer built or maintained, and the databases being used are no longer maintained. Thus the source data should not change. Apart from any pillars that are destroyed in the future, the data should be static.
This import is planned to be performed either using JOSM or the bulk_upload/upload Python scripts.
Additionally, a Leaflet based slippy map is provided showing the current state of all OSM pillar points and related OSM man_made=survey_point nodes for aid in pre/post import review, tracking progress and viewing and comparing data for any hand applied fixes.
Data Preparation
The Data is loaded, parsed and processed with R. The code is available on github, along with details of the algorithms used.
The OS triangulation data coordinates are supplied in OSGB36 Northing/Easting format with ODN heights. The R sf library, and the underlying PROJ library, are used to convert the OSGB36+ODN coordinates into ETRS89+EGM96 utilising OSTN15 NTv2 data.
The OS benchmark data coordinates are supplied in British National Grid format, including grid squares. The R osbng library supplied by the OS along with sf/PROJ is used to convert these to ETRS89.
The OSM man_made=survey_point nodes are extracted from geofabrik data using osmosis.
All further workings are done in ETRS89.
The code uses the OS triangulation station data to collate and locate the pillars. It then correlates the OS benchmark data against those pillars to extract flush bracket numbers associated with those pillars. Sadly the benchmark flush bracket data is both inconsistent and incomplete, but does provide a large quantity of useful additional data (flush bracket numbers) that can be added as ref:os tags to the OSM nodes.
Data Reduction & Simplification
The resulting pillar data is then correlated against the UK OSM data for type man_made=survey_point, for any OSM point that is either marked as a pillar or of unknown type (that is, anything explicitly not a pillar is removed from the processing).
Only OS pillars that do not have an OSM survey_point node within 15m are thus classified as a 'new' trigpoint, and will be considered part of the automated bulk import.
N.B.: Other resulting categories of node the code generates OSC files for, but are not intended to be part of this import are:
- 'good' for pillars that already align well with OSM nodes, and thus need no further work.
- If we consider all tags we would like applied to nodes, there are presently no 'good' nodes in OSM, as we are introducing some new tags - but there are approx. 307 nodes that are 'very close'.
- 'review' for any pillars that look similar to an OSM node, but are inconsistent, and thus could do with human review
- 'edit' for any OSM nodes that could potentially be automatically updated to align their positions and tags with the OS data - but are not planned as part of this import.
Tagging Plans
All new nodes will be created as man_made=survey_point nodes, placed at the coordinates derived from the OS triangulation data Easting/Northing. The following tags will be included in all new nodes:
| Source Attribute | Tag | Notes |
|---|---|---|
| Trig Name | name | The common name |
| New Name | ref:os | The unique OS new style identifier |
| TYPE OF MARK | survey_point:structure | 'pillar' in this instance |
| HEIGHT | ele | EGM96 elevation in metres |
| " | ele:EGM96 | EGM96 elevation in metres |
| " | ele:ODN | ODN elevation in metres |
| " | ele:WGS84 | WGS84 elevation in metres |
| - | note | Do not move this node, see -
https://wiki.openstreetmap.org/wiki/OS_pillar_trigpoint_import |
- Note: the ref:os is in effect a new tag for man_made=survey_point / survey_point:structure=pillar nodes. Not only will it hold the unique OS triangulation data 'New Name' for the node, but can also later be used for verification and conflation to determine which OSM nodes have already been imported, ammended or reviewed, and which have not. There are presently only 5 existing survey_point=man_made nodes that contain a ref:os tag, and all of these currently contain the old-style unique OS reference, so at present, in effect, already contain the unique identifier, and can be easily updated to contain the new style reference.
- Note: the ele tags variety are intended to satisfy the OSM ele tag requirement to be stored in EGM96, whilst also providing other data conversions (such as ODN) for ease of future application usage.
- Note: the note tag is inspired by the similar trigpoint import for France. If we presume that the OS data is as accurate as any other data we will get for a trigpoint position, then requesting that this data is not updated in the future (without good cause and justification) does not feel overly onerous.
The following tags are optional, depending on the completeness of the data available for each node.
| Source Attribute | Tag | Notes |
|---|---|---|
| DESCRIPTION (bm) | ref | The flush bracket number derived from the benchmark data, if available |
Many exsiting OSM nodes already contain this ref containing flush bracket information.
Changeset Tags
The following tags will be applied to the changeset:
| Key | Value |
|---|---|
| comment | Add all missing UK triangulation pillars from the OS dataset |
| created_by | https://github.com/grahamwhaley/OSM_UK_trigpoints |
| import | yes |
| source:url | https://www.ordnancesurvey.co.uk/geodesy-positioning/legacy-data/trig-search |
| source:date | 2026-05-20 (to be set at actual import date) |
| import:page | https://wiki.openstreetmap.org/wiki/OS_pillar_trigpoint_import |
| source:license | OGL-UK-3.0 |
Data Transformation
All processing is done with R. The code can be found on github.
The OS data is imported from CSV files and converted from the UK grid co-ordinates to ETRS89. It is then filtered and correlated and sets of nodes for import or potential conflation or human review are generated as OSC XML change files. Only new nodes will be considered for this import.
Data Transformation Results
OSC XML files are posted on the github repository.
Data Merge Workflow
The plan is to merge the data with OSM via JOSM or the Python upload scripts. Before the full import it is planned to:
- Do dry runs on the dev server API
- Do one or more initial small imports to verify correct results and reduce any necessary rollback, for instance we could start by importing for small UK counties (Isle of Wight, Rutland etc.).
Team Approach
Presently this is a solo effort, but input, review and help is more than welcome.
Workflow
The workflow will be:
- Normalise the current 5 ref:os tags in OSM to match this import scheme
- Check these 5 tags are then correctly identified by the tools and appear correctly on the slippy map.
- Enable 'full goodness' checking in the tools, now we have some 'good' nodes to reference.
- Re-generate the OSC files to take into account the 5 new 'good' nodes and review for correctness
- Review performed by manual inspection of the XML and visual inspection both on the slippy map and by loading the OSC files into JOSM.
- Perform test imports of small datasets (subsets) onto the dev server.
- Review
- Inform community of pending import
- Perform a small import to the main server.
- Review
- Re-process fresh OSM data and check for correct import and expected changes in OSC files and slippy map.
- Update github and OSM wiki page.
- Inform community of import
- Perform test import of remaining nodes to dev server
- Perform import of remaining nodes to main server.
- Review
- Re-process fresh OSM data and check for correct import and expected changes in OSC files and slippy map.
- Update github and OSM wiki page.
If any revert is necessary then help will be asked for. Given the imports should only be making new nodes and all those nodes should be identifiable from the ref:os tag (apart from the 5 existing nodes), there should not be any major challenges reverting the changeset using scripts such as revert.pl for instance.
The current analysis of the data shows the import will add something in the region of 4437 new nodes.
Conflation
This import is intended to avoid all conflation with exsting nodes. The code tries to identify OS pillars that have no current representation in OSM.
There are 5 current OSM nodes that will be manually edited to change their existing ref:os tags from containing old style OS pillar references (STATION NAME) to new style OS pillar references (New Name).
The code does generate a list of edit nodes which are suitable candidates for automatic import with conflation (merging), but this import plan does not cover those nodes. If this import is successful then a second import plan may be constructed to cover the mergeable nodes - presently around 772 nodes.
There are around 307 nearly 'good' nodes, and a hand driven effort may be undertaken to bring those nodes into line with the imported nodes after the import has taken place.
QA
Notification of this project was discussed on the talk-GB mailing list. Further notifications and discussion will happen via that list.
Discussion
The preliminary post to the community forum was sent on 2026-06-09 and can be found here.