Description
Flag crossing only for strictly opposite signs whose difference is less than 180, and touching when either endpoint is zero.
Longitude is an angular coordinate with a seam and equivalent values separated by full turns. Interval direction, endpoint inclusion, and half-turn policy must be fixed before comparing or averaging longitudes.
Flag crossing only for strictly opposite signs whose difference is less than 180, and touching when either endpoint is zero.
When to use this tool
Use Geography: Prime Meridian Crossing Flag when you need a longitude normalization, interval, or seam-policy calculation.
How to use the tool and how it works
- Enter fromDegrees, toDegrees. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read result. Expand result to inspect the returned fields.
Require bounded longitudes in degrees and reject an exact 180-degree difference as ambiguous. Flag crossing only for strictly opposite signs whose difference is less than 180, and touching when either endpoint is zero.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| fromDegrees | From Degrees Unit: deg. | Required. Finite number. |
| toDegrees | To Degrees Unit: deg. | Required. Finite number. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| result | Object containing the calculated members; expand to inspect the fields below. | Required. Object. |
| result.crossesPrimeMeridian | Crosses Prime Meridian | Calculated result member: boolean. |
| result.touchesPrimeMeridian | Touches Prime Meridian | Calculated result member: boolean. |
{
"input": {
"fromDegrees": -10,
"toDegrees": 10
},
"output": {
"result": {
"crossesPrimeMeridian": true,
"touchesPrimeMeridian": false
}
}
}Limitations and assumptions
- This is a longitude-only short-arc convention. It does not inspect latitude, actual routes, pole crossings, or whether a geodesic reaches the prime meridian elsewhere.
- Outputs are nested inside result. 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 a full spherical or ellipsoidal geometry method for routes and areas. Retain an explicit seam and endpoint policy when splitting, sorting, or averaging geographic data.
References
Similar or alternative tools
- Geography: Longitude Interval Span With Wrap
Use that policy for identical values, preserve a +360 difference as full width, and otherwise wrap the difference modulo 360.
- Longitude Halfturn Tie Direction Label
Wrap to minus from modulo 360.