[Xastir] Xastir Digest, Vol 54, Issue 28

[Guy Story KC5GOI]

Curt, I tried it with the online maps this evening and had the same issue.
If the error was within 50 meters I would not sweat it but it is off by a
mile in some cases.  I still think I am not getting the tie points close
enough.  Based on what I learned on WinAPRS if you take the tie points and
use them to draw a box, if it was more rectangular than square, the image
would be altered and cause posits to not place correctly on the image file
but are on the money with the Tiger files.  I could probably do better on
the distance of the tie points too.  I am not completely to the upper left
and lower right as I probably could be.  I am trying to use road
intersections as reference points to find tie points.

That said, you theory on datums could be right too.  I have no idea what
Google is using for their datum format on their maps.  I know from
Geocaching that if the datums differ then the locations are not going to
match.

I will play with this more this week.  Time for shutting down tonight.

Message: 2
> Date: Sun, 23 May 2010 09:58:12 -0700 (PDT)
> From: "Curt, WE7U" <curt.we7u at gmail.com>
> To: Xastir - APRS client software discussion <xastir at lists.xastir.org>
> Subject: Re: [Xastir] Xastir Digest, Vol 54, Issue 27
> Message-ID: <alpine.LNX.2.00.1005230956190.960 at wapiti.we7u.net>
> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
>
> On Sun, 23 May 2010, Guy Story KC5GOI wrote:
>
> > I got my maps working yesterday evening.  There was not much of a
> learning
> > curve for me on this one since WinAPRS uses the same format with the
> > exception of the image size field and that was easy.  I am currently
> having
> > tie point accuracy issues but I can get that taken care of.  My maps are
> not
> > lining up to the Tiger maps, sometimes off by close to a half mile and
> > distorted image.
>
> Which Tiger maps?  The online ones?  Be aware they use an odd
> projection (sine) so they are more accurate at the middle of the
> image as far as Xastir is concerned than the edges.
>
> If you're talking about Tiger Shapefile downloaded maps, it's
> possible you're dealing with a datum difference between the two
> types of maps.
>
> --
> Curt, WE7U.                         <http://www.eskimo.com/~archer<http://www.eskimo.com/%7Earcher>
> >
>    APRS:  Where it's at!                    <http://www.xastir.org>
>   Lotto:  A tax on people who are bad at math. - unknown
> Windows:  Microsoft's tax on computer illiterates. - WE7U.
> The world DOES revolve around me:  I picked the coordinate system!"
>
>

-- 
73

Guy Story KC5GOI
kc5goi at gmail.com