Re: [NTLK] Help with GPS MAP process (VERY,VERY LONG POST)

From: Edward Johnson (radar9999_at_aol.com)
Date: Mon Apr 11 2005 - 16:03:15 PDT


Hey Mike!
Outstanding work, my friend. Maptech does not display Lat/Long to that
additional level of precision. That could have been my problem (with
the NaN's) all along. What website are you using for maps? Are they
free or are you paying a subscription? One of my trials included using
the decimal versions of the Lat Longs, but I'm guessing that even they
did not have enough precision. FYI my test map is very small, only
about 480 x 480 pixels for simplicity's sake.

Another funny thing I noticed with the Maptech maps was that the start
point matters with respect to what the actual map I used ends up
looking like. My map starts out at the Ojai Valley Estates Mobile Home
Park, and then I navigate the map SW>S>S to get the map I used for my
data. If I start in downtown Ojai & navigate the map S>S>W>W>W>W>W>W
the map ends up different. So, with Maptech, your start point
determines the final picture of your map, hmmmm.

What I need in order to get a replicate-able map is a way to anchor the
vertex of the map at a particular location, that way when I transfer
the map to Graphic Converter I have a way to go back and verify the
coordinates. What is your source? Did you buy the Nat'l Geographic
software?

Semper Fi!

Ed Johnson

A Smart man learns from his mistakes. A Wise man learns from other
peoples mistakes. Be Wise!
On Apr 10, 2005, at 6:23 PM, newtontalk_at_newtontalk.net wrote:

> From: Michael Briley <mike_at_maxwell.phys.uwosh.edu>
> Subject: Re: [NTLK] Help with GPS MAP process (VERY,VERY LONG POST)
> Date: Sun, 10 Apr 2005 11:25:52 -0400
>
> Hi Ed,
>
> You have to have better coordinates as inputs. One second of latitude
> is about 100 feet! Also, going by your descriptions, I'm not sure the
> input lat/long values were spot on. I've taken the liberty of looking
> them up myself and the values below lead to a useable solution.
> Whether it's the correct solution depends on my getting the streets
> right and your measurements of the corresponding pixel locations.
>
>> Calibration Point 3 (Upper Lft ref pt) --La Luna Dr & Unk dead end
> road
>> Lat 34 26 17 (North)
>> Long -119 17 17 (West)
>> Pixel coordinates (r/d) 90/29
>
> lat: 34 26 16.47
> log: -119 17 20.57
>
> The dead end road is Oakwood. Your point is about 90 feet northeast
> of Oakwood & Cottonwood.
>
>> Calibration Point 1 (Lft ref pt) -rte 33 & villanova rd
>> Lat 34 25 33 (North)
>> Long -119 17 17 (West)
>> Pixel coordinates (r/d) 91/387
>
> (assuming west Intersection of 33 & Villanova:)
> lat: 34 25 32.70
> log: -119 17 20.42
>
> Your coords are nearer the intersection of Old Grade Rd. & Villanova.
>
>> Calibration Point 2 (Lower Rt ref point) villanova rd & unk rd
>> Lat 34 25 46 (North)
>> Long -119 16 21 (West)
>> Pixel coordinates (r/d) 454/276
>
> (assuming unknown road is Rancho La Vista:)
> lat: 34 25 46.55
> log: -119 16 25.94
>
> Your coords are about 430 feet east of this point and a few feet off
> the road (i.e., this one was way off).
>
> One trick for neighborhood maps, especially if your map software
> isn't precise, is to actually go to the reference points with the GPS
> and get the coordinates that way. You can be sure they're accurate
> then!
>
> I hope this helps,
> -Mike
>

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