wgs84

# WGS84 Use this skill for practical work with WGS 84 longitude/latitude coordinates. WGS 84 usually refers to the global geographic reference system commonly exposed as `EPSG:4326` in GIS software. It is the right default for GPS-style coordinate exchange, but it is not the right answer for every display or measurement workflow. ## What This Skill Does - Explain what WGS 84 is and when to use it. - Validate longitude/latitude numeric ranges. - Check whether a coordinate pair is likely `lon,lat` or `lat,lon`. - Recommend a UTM zone and EPSG code for projected analysis. - Flag when a coordinate falls inside mainland-China extents where `GCJ-02` / `BD-09` confusion is common. - Recommend whether to keep WGS84, use Web Mercator for display, or switch to a projected CRS for analysis. - Explain when to keep data in `EPSG:4326` and when to reproject. - Hand off file-based reprojection steps to `qgis` when execution is required. ## Standard Workflow 1. Confirm whether the input is WGS 84 already, or just "GPS coordinates" by assumption. 2. State the expected tuple order explicitly: `lon,lat` or `lat,lon`. 3. Validate numeric ranges before discussing conversion. 4. Decide the task type: - storage or API exchange - web map display - distance/area/buffer analysis - regional engineering or survey workflow 5. Keep `EPSG:4326` for exchange/storage unless the task needs projected units. 6. If analysis needs meters, recommend a suitable projected CRS such as a local CRS or UTM zone. ## Practical Commands ### Validate a WGS84 coordinate pair ```bash python3 {baseDir}/scripts/wgs84_tool.py validate --lon 116.4074 --lat 39.9042 ``` ### Check whether a pair is probably `lon,lat` or `lat,lon` ```bash python3 {baseDir}/scripts/wgs84_tool.py guess-order --a 116.4074 --b 39.9042 python3 {baseDir}/scripts/wgs84_tool.py guess-order --a 39.9042 --b 116.4074 ``` ### Recommend a UTM zone and EPSG code from WGS84 coordinates ```bash python3 {baseDir}/scripts/wgs84_tool.py utm --lon 116.4074 --lat 39.9042 python3 {baseDir}/scripts/wgs84_tool.py utm --lon -122.478255 --lat 37.819929 ``` ### Flag China mapping offset risk ```bash python3 {baseDir}/scripts/wgs84_tool.py china-check --lon 116.4074 --lat 39.9042 ``` ### Recommend the right CRS for a concrete task ```bash python3 {baseDir}/scripts/wgs84_tool.py recommend --lon 116.4074 --lat 39.9042 --task exchange python3 {baseDir}/scripts/wgs84_tool.py recommend --lon 116.4074 --lat 39.9042 --task analysis python3 {baseDir}/scripts/wgs84_tool.py recommend --lon 116.4074 --lat 39.9042 --task web-map ``` ## Decision Rules - Prefer `EPSG:4326` for interoperable storage, APIs, logs, and exchange. - Prefer a projected CRS in meters for buffering, area, distance, and nearest-neighbor analysis. - Prefer `EPSG:3857` only for web-map display compatibility, not for accurate measurement. - Do not assume a pair is WGS 84 just because it contains two decimals; confirm source system when accuracy matters. - Do not assume all systems interpret `EPSG:4326` axis order the same way; many practical APIs use `lon,lat` even when standards prose differs. - In mainland China workflows, explicitly check whether the source is raw WGS84 or app-level `GCJ-02` / `BD-09`. - Treat `GCJ-02` and `BD-09` as mapping offset systems, not simple aliases for `EPSG:4326`. ## What To Return - The interpreted coordinate order. - Whether the values are valid WGS84 longitude/latitude ranges. - Whether keeping `EPSG:4326` is appropriate for the task. - If not, recommend the target CRS and explain why. - If using UTM, provide zone number, hemisphere, and EPSG code. - If the point is in mainland China, include a short warning about `GCJ-02` / `BD-09` ambiguity when relevant. ## When Not To Use - Reverse geocoding or coordinates to address lookup: use `geocode`. - File-based GIS conversion or batch reprojection: use `qgis`. - General CRS comparison beyond WGS84-centered guidance: use `project`. - Navigation routing, POI search, or map reviews. ## OpenClaw + ClawHub Notes - Keep examples generic and reproducible. - Do not hardcode private paths, real device traces, or private datasets. - For clawhub.ai publication, keep versioning/changelog semver-driven and examples standards-based. ## Reference Docs In This Skill - Read `{baseDir}/references/wgs84-reference.md` for concise CRS comparison and common failure cases.