Computing heading

Colin Putney cputney at
Sun Jan 4 17:54:03 UTC 2004

On Jan 4, 2004, at 9:34 AM, David T. Lewis wrote:

> On Sun, Jan 04, 2004 at 12:41:19AM -0800, Jack Johnson wrote:
>> I was messing around with EToys and grabbed an arrow morph and a 
>> couple
>> of ellipses and wanted to have the arrow morph automatically place
>> itself between the two ellipses and point from one to the other.
>> The placement was easy, but I had trouble computing the heading.  I 
>> did
>> come across a formula used for computing a bearing based on two map
>> coordinates:
>> tc1=mod(atan2(sin(lon1-lon2)*cos(lat2),cos(lat1)*sin(lat2)-
>> sin(lat1)*cos(lat2)*cos(lon1-lon2)),2*pi)
>> which would work just fine, but being relatively new to Squeak I'm at 
>> a
>> loss for how to implement it, or how to even find out if/how Squeak
>> implements the atan2 function.
>> Any pointers or suggestions?
>> -Jack
> Hi Jack, welcome to Squeak.
> Bert gave you a good answer for the problem you are trying to solve, 
> but as a
> newcomer to Squeak you may also be interested in knowing "how do I 
> write
> this math formula in Squeak?". To answer that, I'm going to drop down 
> a level
> into the Smalltalk language that is working underneath the EToys 
> envinroment.

Hi Jack,

Just in case you're more interested in the diagram than the math, I'd 
also suggest having a look at Ned Konz' Connectors package. It's very 
good at dealing with ellipses connected by arrows.

The Connectors page is here: <>.

You can install Connectors via SqueakMap, which is explained here:

Have fun!


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