Longitude Halfturn Tie Direction Label Tool

Description

Wrap to minus from modulo 360.

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.

Wrap to minus from modulo 360.

When to use this tool

Use Longitude Halfturn Tie Direction Label when you need a longitude normalization, interval, or seam-policy calculation.

How to use the tool and how it works

Enter from, to, preferEast. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read difference, tied. Inspect tied before interpreting the associated values.

Wrap to minus from modulo 360. At exactly 180 return +180 when preferEast is true or -180 otherwise; elsewhere return the representative below 180 and above -180, plus the tied flag.^[1]

Input field	Meaning and units	Accepted input
from	From	Required. Finite number.
to	To	Required. Finite number.
preferEast	Prefer East	Required. Boolean.

Output field	Interpretation	Returned shape
difference	Difference	Required. Finite number.
tied	Tied	Required. Boolean.

json

{
  "input": {
    "from": 0,
    "to": 180,
    "preferEast": false
  },
  "output": {
    "difference": -180,
    "tied": true
  }
}

Limitations and assumptions

Angles are degrees, with positive differences interpreted eastward. Tie handling is exact floating-point equality; no geographic path or coordinate bounds are checked.
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

Calculation and input contract: geography/longitude-halfturn-tie-direction-label — tool.io

Similar or alternative tools

Longitude Signed Unwrapped Representative
Compute turn as floor((reference-longitude+180)/360), add 360 times turn to longitude, and return that unwrapped representative.
Longitude Arc Complement
Return the smaller of their absolute difference and its 360-degree complement as shortArcDegrees, and 360 minus that result as longArcDegrees.