Coordinate Converter

A production-ready Python/Flet desktop application that converts coordinates between Swedish and global reference systems, including a bespoke RR92 (RFN) Helmert transformation, SWEN17_RH2000 height support, and a CSV batch CLI.

Status: reference implementation targeting Python 3.11+ on macOS. Most features run cross-platform, but packaging/signing is not included.

Features

• Flet desktop UI with coordinate source/height selectors, precision controls, and a live OpenStreetMap preview via Leaflet.
• Robust free-text parser for DD, DMS, DDM, RT90 2.5 gon V, MGRS, and geocentric XYZ (WGS84 + RR92).
• Canonical transformation engine using PyProj with cached Transformer pipelines and a custom exact-rotation 7-parameter Helmert implementation for RR92.
• Ellipsoidal vs orthometric height handling with SWEN17_RH2000 geoid support.
• CSV batch CLI supporting multiple target CRS outputs in a single run.

Quick Start

./start_app.sh

The helper script creates (or reuses) a local .venv, installs dependencies via uv, and launches the desktop UI. Pass additional arguments to forward them to the application entry point.

The first run downloads the SWEN17 geoid grid if PROJ is configured to fetch remote resources. If the grid is missing a warning banner is shown.

Usage

Desktop UI

make run

Choose the Input coordinate source and Input height reference selectors to spawn the relevant fields (e.g., WGS84 lat/lon, RT90 northing/easting, XYZ, MGRS). After entering values, click Convert or press Enter. The Output coordinate and Output height system selectors mirror the same options and render the chosen representation only. Geographic outputs can be displayed as DD, DDM, or DMS via the format dropdown.

Keyboard shortcuts (numeric input fields):

• ↑/↓: ±1 in the focused box
• Shift + ↑/↓: ±10 in the focused box
• Enter / focus-out: commit edits and refresh map

CSV CLI

python -m cli.csv_convert --in samples/input.csv --out output.csv \
  --from SWEREF99_GEO --to WGS84_GEO,RR92_XYZ,RT90_3021 --height RH2000

• --from supplies the default CRS when a row cannot be inferred.
• --to may contain multiple comma-separated targets.
• Height selection currently accepts ELLIPSOIDAL and RH2000. RFN heights are stubbed until authoritative parameters are published.

Unknown columns are preserved, and row-level errors are appended to a summary written to stderr.

Coordinate Reference Systems

Code	Description
WGS84_GEO	EPSG:4326 latitude/longitude (degrees).
SWEREF99_GEO	EPSG:4619 latitude/longitude.
RT90_3021	EPSG:3021 RT90 2.5 gon V (northing/easting).
WGS84_XYZ	EPSG:4978 Earth-Centered Earth-Fixed cartesian.
RR92_XYZ	Rikets referenssystem 1992 geocentric cartesian.
MGRS	WGS84 Military Grid Reference System strings.

Height Systems

• Ellipsoidal: h above GRS80/WGS84 ellipsoid.
• RH2000: H = h − N using the SWEN17_RH2000 geoid grid.
• RFN: Placeholder module pending publication of official transformation parameters; see core/height_rfn.py.

Development

make fmt   # black
make lint  # ruff
make test  # pytest

Project layout:

src/
  app/main.py              # Flet desktop app entry
  app/map_view/leaflet.html# Leaflet map scaffold
  core/                    # Parser, CRS registry, transforms, heights
  cli/csv_convert.py       # CSV batch tool

Tests & Samples

• Parser: tests/test_parser.py
• Helmert: tests/test_helmert_rr92.py
• Height placeholder: tests/test_height_rfn.py
• CLI: tests/test_csv_cli.py

Sample CSVs live under tests/data (created during tests).

Screenshots

Add screenshots of the UI in docs/ once the visual design is finalised.

License

Released under the MIT License. See LICENSE.