[postgis-users] I can't make sense of this.

[Ronald Phillips]

Ok, let me guess, then. I don't need to transform at all; the Google Maps API is using SRID 4326 for the coordinates. No wonder it didn't give sensible results -- I was asking nonsense. 

What a relief! 

Thank you, everyone. I couldn't find a good search term that brought up this simple fact. I'll try again, and I'm sure it will be fine.

Ron

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Paul Ramsey
Sent: Thursday, May 20, 2010 1:00 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] I can't make sense of this.

While the underlying map tiles in GMaps are mercator, the actual API
only talks to you in geographics. This causes many people, including
you, confusion. Either of the form of "the map is in lat lon" (it's
not) or, in your case "the coordinates I'm working with are in the
Google projection" (they aren't, they are WGS84).

P.

On Thu, May 20, 2010 at 9:55 AM, Ronald Phillips
<rphillips at summitengineer.net> wrote:
> I want to provide a geometry that was input from Google Maps (SRID 3857) for
> GPS units (SRID 4326). How should I do that?
>
>
>
> I hated to post this, frankly. I know it's a "thinko;" I'm not understanding
> the concept. If I describe a geometry in SRID 3857, then it seems to me that
> that point would have a slightly different description in SRID 4326.
> Instead, they're wildly different. So, I know I am misunderstanding in some
> basic way.
>
>
>
> Ron
>
>
>
> ________________________________
>
> From: postgis-users-bounces at postgis.refractions.net
> [mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Emilie
> Laffray
> Sent: Thursday, May 20, 2010 12:48 PM
> To: PostGIS Users Discussion
> Subject: Re: [postgis-users] I can't make sense of this.
>
>
>
> Why would you expect them to be similar? There are different sets of
> coordinates.
> Your first set of coordinates looks like wgs84 but you set the srid to
> Google srid.
> It doesn't make sense.
>
> On 20 May 2010 17:38, "Ronald Phillips" <rphillips at summitengineer.net>
> wrote:
>
> SELECT
>
>             ST_AsText(
>
>                         ST_GeomFromText('POINT(-81.064544 40.28787)', 3857)
>
>                         )
>
> AS goog,
>
>             ST_AsText(
>
>                         ST_Transform(
>
>                                     ST_GeomFromText('POINT(-81.064544
> 40.28787)', 3857)
>
>                         , 4326)
>
>             )
>
> AS gcs
>
>
>
> 3857 is "Google's" SRID, and 4326 is a fairly standard GPS SRID. I'm getting
> this:
>
>
>
> Goog: "POINT(-81.064544 40.28787)";
>
> Gcs: "POINT(-0.000728215188753794 0.000361912093851508)"
>
>
>
> What am I doing wrong, that they're so different?
>
>
>
> Ronald Phillips, B.S., M.S.
>
> Programmer/Analyst
>
>
>
> Summit County Engineer
>
> 538 E. South St.
>
> Akron OH 44311
>
> 330.643.8061
>
> http://www.linkedin.com/in/rwphillips
>
>
>
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