CGCS2000

Use this skill for practical reasoning about the China Geodetic Coordinate System 2000.

CGCS2000 is a China-centered geodetic reference framework used widely in surveying, mapping, and domestic GIS workflows. In many GIS tools, the geographic form is commonly represented as EPSG:4490, but real work often also involves projected CGCS2000 variants, especially Gauss-Kruger zone systems.

What This Skill Does

• Explain what CGCS2000 is and when it is the right source or target CRS.
• Distinguish geographic CGCS2000 from projected CGCS2000 variants.
• Identify whether the user likely means EPSG:4490 or a projected China CRS in meters.
• Check for common mistakes involving axis order, units, and false assumptions about "same as WGS84".
• Compare CGCS2000 with WGS84, GCJ-02, and BD-09.
• Recommend whether to keep the data in geographic coordinates or move to a projected CRS for analysis.
• Hand off file-based conversion and batch reprojection steps to qgis when execution is needed.

Standard Workflow

1. Confirm the actual input form:
   • longitude/latitude in degrees
   • projected easting/northing in meters
   • map-app coordinates that may actually be GCJ-02 or BD-09
2. Ask whether the user needs:
   • storage or exchange
   • web display
   • engineering, surveying, or measurement
   • file-based reprojection
3. State the exact CRS level being discussed:
   • CGCS2000 datum/reference frame
   • EPSG:4490 geographic CRS
   • projected CGCS2000 CRS with zone/projection details
4. Validate units and order before recommending conversion.
5. If the task needs meters, recommend the exact projected CRS rather than only saying "CGCS2000".

Decision Rules

• Use EPSG:4490 when the data is truly geographic CGCS2000 longitude/latitude in degrees.
• For engineering, cadastral, measurement, or local analysis work, prefer the correct projected CGCS2000 CRS in meters.
• Do not say "CGCS2000" alone when the task requires a projected CRS; include zone/projection details.
• Do not treat GCJ-02 or BD-09 as standard CGCS2000 coordinates.
• Do not assume consumer-map coordinates in China are raw CGCS2000 or raw WGS84.
• If the source is unknown, explicitly call out datum/projection uncertainty before suggesting a transformation.

Common Cases

The user says "CGCS2000 coordinates"

Interpret carefully:

• It may mean EPSG:4490 longitude/latitude in degrees.
• It may mean a projected CGCS2000 coordinate system in meters.
• It may be shorthand from a local data specification that still requires the exact EPSG or projection name.

The user wants to compare CGCS2000 and WGS84

• They are close for many practical GIS use cases, but they are not interchangeable by definition in every precise workflow.
• If regulatory, survey, or engineering accuracy matters, keep the stated source datum and use the required official CRS.
• If the task is generic storage or API exchange, explain whether the downstream system expects CGCS2000 or WGS84 explicitly.

The user has China map coordinates from an app

• First check whether the source is actually GCJ-02 or BD-09.
• Do not label app-map coordinates as CGCS2000 without evidence.
• If the request is about web maps or app SDKs, mention offset-system ambiguity early.

The user wants projected analysis

• Ask for the area of use and the current CRS.
• Recommend the exact projected CGCS2000 CRS with units in meters.
• If the user only has files and wants execution, use qgis.

What To Return

• The interpreted source CRS, with exact name or EPSG when possible.
• Whether the coordinates are likely geographic degrees or projected meters.
• Whether EPSG:4490 is appropriate, or whether a projected CGCS2000 CRS is needed instead.
• Any risk that the data is actually GCJ-02 or BD-09.
• A concrete next step for reprojection, exchange, or validation.

When Not To Use

• Reverse geocoding or address lookup: use geocode.
• QGIS file-based processing or batch reprojection: use qgis.
• General CRS comparison across many systems when CGCS2000 is not the focus: use project.
• GPS-only WGS84 validation with no China-specific CRS question: use wgs84.

OpenClaw + ClawHub Notes

• Keep examples generic and standards-based.
• Do not hardcode private datasets, machine paths, credentials, or proprietary basemap assumptions.
• For clawhub.ai publication, keep examples reproducible and version/changelog updates semver-driven.

Reference Docs In This Skill

• Read {baseDir}/references/cgcs2000-reference.md for quick comparison points, projected-workflow guidance, and common failure cases.