fieldGRID shows a position as latitude/longitude, Irish Grid, British National Grid, UTM and Plus Code. This page records the third-party material behind those conversions and the notices we owe. The mobile apps show the same notices in-app; this page is in addition to that.
1. What this covers
The fieldGRID web portal converts coordinates in your browser for display only. WGS84 latitude/longitude stays the stored, authoritative position; grid references are never written back. The portal does not include or send you the OSTN15 grid or any other datum-shift grid file. The Android and iOS apps do include OSTN15 (section 4).
| Output | Web portal | Android and iOS apps |
|---|---|---|
| British National Grid | Seven-parameter Helmert transform from WGS84 to OSGB36, then Airy 1830 transverse Mercator | OSTN15 grid transformation, then Airy 1830 transverse Mercator |
| Irish Grid (TM75) | Seven-parameter Helmert transform, then Airy Modified transverse Mercator | Inverse of the published EPSG:1953 seven-parameter operation, then Airy Modified transverse Mercator |
| UTM | WGS84 transverse Mercator, with the Norway and Svalbard zone exceptions | Same |
| Plus Code | Open Location Code library | Open Location Code library |
2. Accuracy
fieldGRID is a field-reference tool. Grid references are not survey-grade, cadastral or legal-boundary accurate, and must not be used where official coordinates are required. Four different things limit accuracy, and they should not be confused:
- Transformation method. A single seven-parameter Helmert transform, as used on the web, is approximate and can differ from the official transformation by several metres or more. OSTN15 (Great Britain) and the official Irish transformations are more accurate; the web portal does not use them.
- Operation accuracy. Even the published EPSG:1953 operation used by the mobile apps for the Irish Grid states an accuracy of 1 m.
- Device GNSS accuracy. Phone GNSS is commonly several metres horizontally, regardless of how exactly the conversion is calculated.
- WGS84 and ETRS89. The mobile conversions treat WGS84 GNSS coordinates as ETRS89. The difference depends on the date and is roughly a metre in Great Britain and Ireland. It is not corrected.
Agreement between our code and an independent implementation such as PROJ says nothing about real-world accuracy and is not a survey-grade claim.
3. EPSG Geodetic Parameter Dataset
The projection and datum parameters for the Irish Grid (EPSG:29903, and EPSG:1953 in the mobile apps) and British National Grid (EPSG:27700) come from the EPSG Geodetic Parameter Dataset. The EPSG Dataset is owned by the International Association of Oil and Gas Producers (IOGP). See the EPSG Terms of Use.
The EPSG Dataset is provided “as is”, without warranty of any kind, and IOGP accepts no liability for its use. If you pass on EPSG-derived data, you must pass on those terms. fieldGRID is not endorsed by or affiliated with IOGP.
4. Ordnance Survey OSTN15 (mobile apps only)
The Android and iOS apps ship a data file derived from the OSTN15 NTv2 transformation grid, obtained through the PROJ-data distribution (copyright holder listed there as Ordnance Survey UK, licence BSD-2-Clause). fieldGRID converted it into its own compact binary format. The web portal does not ship or send this file.
© Copyright and database rights Ordnance Survey Limited 2016. All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: (1) redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer; (2) redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
fieldGRID is not endorsed by or affiliated with Ordnance Survey.
5. Plus Codes (Open Location Code)
Plus Codes are produced with the open-location-code JavaScript library (version 1.0.3 on the web), which is licensed under the Apache License, Version 2.0. Copyright 2014 Google Inc. The licence text is at apache.org/licenses/LICENSE-2.0. The mobile apps use their own Open Location Code implementations under the same licence terms.
6. proj4js
The web portal uses proj4js (version 2.22.0) for map projections, licensed under the MIT licence. Copyright © proj4js authors (Mike Adair, Richard Greenwood and contributors). The software is provided “as is”, without warranty of any kind.
7. Development tools not distributed
PROJ and pyproj were used on development machines only, to generate and cross-check test results. They are not part of the fieldGRID web portal or apps, so their licences are not runtime obligations here.
8. Contact
Questions about these notices: contact@fieldgrid.cloud. For how we handle personal data, see the Privacy notice.