---
name: "GIS::Distance::GreatCircle"
section: "3pm"
platform: "linux"
package: "libgis-distance-perl"
version: "0.20-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/GIS::Distance::GreatCircle"
---

# GIS::Distance::GreatCircle(3pm)

Great circle distance calculations.

## NAME

GIS::Distance::GreatCircle - Great circle distance calculations.

## DESCRIPTION

A true Great Circle Distance calculation.  This was created because the GIS::Distance::MathTrig formula uses Math::Trig's `"great_circle_distance()"` which doesn't actually appear to use the actual Great Circle Distance formula (more likely Cosine).

A faster (XS) version of this formula is available as GIS::Distance::Fast::GreatCircle.

Normally this module is not used directly.  Instead GIS::Distance is used which in turn interfaces with the various formula classes.

## FORMULA

```
    c = 2 * asin( sqrt(
        ( sin(( lat1 - lat2 )/2) )**2 +
        cos( lat1 ) * cos( lat2 ) *
        ( sin(( lon1 - lon2 )/2) )**2
    ) )
```

## SUPPORT

See "SUPPORT" in GIS::Distance.

## AUTHORS

See "AUTHORS" in GIS::Distance.

## LICENSE

See "LICENSE" in GIS::Distance.