# globals

Model was written in NetLogo 3D 6.3.0
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## WHAT IS IT?

This shows how to make turtles move along a perfect sphere. The first procedure moves turtles based a user-defined distance to be travelled; the second moves then based on a user-defined degree measure.

## HOW IT WORKS

We use trigonometry to calculate the turtle's successive positions on the circle.

## RELATED MODELS

Turtles Circling, Circular Path Example

## Comments and Questions

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globals [ radius ] to setup clear-all set radius ( world-width - 2 ) / 2 create-turtles 12 [ ;; move to a random point on the sphere tilt-up ( random 180 ) - 90 fd radius ;; lie tangent to the sphere tilt-down 90 ;; turn again so that not all turtles are moving ;; to north and south poles rt random 360 pen-down ] reset-ticks end to go-distance ask turtles [ arc-forward-by-distance step-size lt random wiggle-range rt random wiggle-range ] tick end to go-angle ask turtles [ arc-forward-by-angle arc-angle lt random wiggle-range rt random wiggle-range ] tick end ;; This procedure moves the turtle to the next point ;; on the sphere the given distance along the curve. to arc-forward-by-distance [dist] ;; turtle procedure ;; calculate how much of an angle we'll be turning through ;; (essentially converting radians to degrees) let theta dist * 180 / ( pi * radius ) ;; turn to face the next point we're going to tilt-down theta / 2 ;; go there fd dist ;; turn to face tangent to the circle tilt-down theta / 2 end ;; This procedure moves the turtle to the next point ;; on the sphere the given angle measure along the curve. to arc-forward-by-angle [angle] ;; turtle procedure ;; turn to face the next point we're going to tilt-down angle / 2 ;; calculate the distance we'll have to move forward ;; in order to stay on the circle. Go there. fd 2 * radius * sin (angle / 2) ;; turn to face tangent to the circle tilt-down angle / 2 end ; Public Domain: ; To the extent possible under law, Uri Wilensky has waived all ; copyright and related or neighboring rights to this model.

There is only one version of this model, created 7 months ago by Peter Nikolyuk.

## Attached files

File | Type | Description | Last updated | |
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globals.png | preview | Preview for 'globals' | 7 months ago, by Peter Nikolyuk | Download |

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