[Loadstone] West bound inconsistency in exploration mode.

Shawn Kirkpatrick shawn at odyssey.cm.nu
Mon Feb 12 09:37:31 GMT 2007

This problem is somewhat common. It happens when points are off at an angle 
from each other. The points you're talking about can probably be found if 
you use north west or south west. What loadstone does is calculate the 
distance and angle from one point to another. It breaks the circle up in to 
8 sections and tries to find a point in the section you want. Sometimes a 
point will be close but just outside the calculated section. The 
calculations should be the same for the opposite direction but doesn't 
always seem to be the case. The only reason I can think of for this is that 
maybe we're getting rounding errors with the floating point number 
calculations. The phone isn't very good at these so that's very possible.

On Mon, 12 Feb 2007, Geoff Waaler wrote:

> Hi y'all (and since I live 35 degrees and change North I get to say this!!),
> I finally put together a test case documenting what I believe to be a bug in
> loadstone when it calculates the nearest point to the West in exploration
> mode.  I am running the "all other phone models" 0.66 version of loadstone
> dated 2/1/07 on a Nokia 6682.  In case it matters my 6682 is locked to
> Cingular with the latest available firmware (4.65).
> I obtained pointshare data for a five mile area around latitude 41.9709,
> longitude -87.7018.  My last_position file points to: 41.99152,-87.655756
> which in English translates to a hundred yards North of Sheridan Rd. and
> Thorndale in Chicago, IL.
> When I begin exploration mode and press the 8 key I am taken to Thorndale
> and Sheridan as expected.  When I press the four key two blocks are skipped
> which will be found on the way back east.  Here are the relevant
> coordinances:
> Eastern point is Sheridan Rd. and Thorndale = 41.990431, -87.655756
> First block West is Kenmore and Thorndale = 41.990431,-87.657156
> Second block West is Winthrop and Thorndale= 41.990431,-87.658556
> Third block West is Broadway and Thorndale = 41.990231,-87.660656
> As you can see Thorndale avenue follows a direct latitudinal line for those
> two blocks where the points are missed during west bound exploration.
> Thorndale avenue drifts a little South when intersecting with Broadway.  Of
> course we are relying on the accuracy of data pointshare managed to obtain,
> but for our purposes it serves to illustrate the problem.  I believe that
> since the six key locates those two points during the virtual East bound
> trip from Broadway it would be reasonable to expect the West bound trip from
> Sheridan to land on those points also.
> Thanks for putting together a great software app!!
> Geoff
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