Description
Return firstX × secondY-secondX × firstY as twiceAreaTerm.
Planar coordinate arithmetic treats values as points on a flat axis system. Applying a determinant or shoelace expression directly to longitude and latitude yields angular-coordinate quantities, not automatically physical area on Earth.
Return firstX × secondY-secondX × firstY as twiceAreaTerm.
When to use this tool
Use Polygon Ring Signed Area Contribution when you need an explicit planar contribution from supplied GeoJSON-style coordinates.
How to use the tool and how it works
- Enter first, second. Keep parallel arrays aligned. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read twiceAreaTerm. Use the output convention below.
Require first and second positions with at least two entries. Return firstX × secondY-secondX × firstY as twiceAreaTerm.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| first | First | Required. Array of finite number; maximum items 256. |
| second | Second | Required. Array of finite number; maximum items 256. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| twiceAreaTerm | One planar determinant contribution, twice its signed shoelace area contribution; not a geodesic area. | Required. Finite number. |
{
"input": {
"first": [
2,
0
],
"second": [
0,
3
]
},
"output": {
"twiceAreaTerm": 6
}
}Limitations and assumptions
- This is one planar shoelace term, twice its signed area contribution; geographic longitude/latitude products are angular-coordinate area terms rather than geodesic area in square meters.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use an appropriate projected or geodesic area method for physical surface area. Sum the complete boundary and validate its geometry when a single local contribution is insufficient.
References
Similar or alternative tools
- Polygon Signed Area Edge Term
Return (firstX × secondY-secondX × firstY)/2 as signedAreaContribution.
- GeoJSON: Ring Distinct Vertex Minimum Check
Compare first and last, count distinct serialized positions, and mark minimumSatisfied only for closure, at least four records, and at least three distinct vertices inside result.