[Loadstone] West bound inconsistency in exploration mode.

Geoff Waaler gwaaler at mindspring.com
Mon Feb 12 15:47:10 GMT 2007


Hi Shawn,

Thanks much for the reply.  My purpose in including the coordinences of the 
points in question was to show that they were not at an angle.  Even if they 
were I do not believe its unreasonable to expect consistency between east 
and west bound traversals.  If I'm experiencing rounding errors because of 
my phone's limited computational skills why do they not occur during East 
bound calculations?  If this is do to the points being at an angle, please 
take a look at the data I provided and let me know how/why the points in 
question are not considered due East/West from one another?

Thanks again.
Geoff

----- Original Message ----- 
From: "Shawn Kirkpatrick" <shawn at odyssey.cm.nu>
To: "General discussion pertaining to the Loadstone GPS program" 
<loadstone at loadstone-gps.com>
Sent: Monday, February 12, 2007 4:37 AM
Subject: Re: [Loadstone] West bound inconsistency in exploration mode.


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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