[postgis-users] RE: area in meters

[Paul Ramsey]

Aha!  Reading it a second time, the problem is that your data is  
actually correct relative to its quoted EPSG CRS!  It is in lat/lon  
order, while PostGIS is expecting it to be in lon/lat order.

So, your coordinate

33.745400 -87.095300 1111.000  0

is saying you are quite close to the south pole, rather than in  
Alabama! And a polygon in lat/lon at the south pole will be a good  
deal smaller than a polygon of the same shape in lat/lon in Alabama!   
Do you have any way of changing your coordinates around when you  
insert into PostGIS?

P

On Mar 15, 2006, at 2:22 PM, <ebcorder at rockwellcollins.com>  
<ebcorder at rockwellcollins.com> wrote:

> Thanks Paul for a really quick response.   This stuff is tough on  
> newbies.
> The Polygon is an unusual shape.... looks kinda like a peanut.  The  
> polygon
> covers an area around Birmingham Ala so I used the UTM Zone 16 2028.
> Thanks for simplifying the query.
>
>
>
>
>> Your query looks correct on its face, so we would have to see the
>> polygon itself to take a more informed guess...
>> P
>
>> PS, a less convoluted SQL statement that returns the same answer:
>
>> select area2d(transform(shapes,2028)) from poly where cell_id = 1;
>
>> On Mar 15, 2006, at 12:53 PM, <ebcorder at rockwellcollins.com>
> <ebcorder at rockwellcollins.com> wrote:
>
>> If anyone can help on this I don't think this value is correct.  I
>> stored a
>> polygon away as Lat/Lon with an SRID=4326.  To obtain the area of the
>> polygon in meters
>>
>> I wrote this query to transform to UTM.
>> geom_test=# select area2d(transform((select shapes from poly  where
>> poly.cell_id=1), 2028));
>>
>>       area2d
>> ------------------
>>  30157076.0118284
>> (1 row)
>>
>> I don't think this is right.   On  a Delorme map tool I get 443  
>> square
>> Kilometers.
>>
>>
>>
>>
>> CREATE TABLE "poly" (
>>             "cell_id"  int4 NOT NULL
>>          );
>>
>>
>> select addgeometrycolumn('poly','shapes',4326,'POLYGON',4);
>>
>> insert into poly (cell_id,shapes)   values (1,
>> GeomFromtext('POLYGON((33.745400 -87.095300 1111.000    0,33.727700
>> -87.099700 1111.000    0,33.718900 -87.102000 1111.000    0,33.708200
>> -87.093700 1111.000    0,33.699400 -87.095900 1111.000    0,33.688700
>> -87.087600 1111.000    0,33.678000 -87.079300 1111.000    0,33.665400
>> -87.060500 1111.000    0,33.663500 -87.049900 1111.000    0,33.652900
>> -87.041600 1111.000    0,33.649100 -87.020500 1111.000    0,33.647200
>> -87.010000 1111.000    0,33.643400 -86.988900 1111.000    0,33.641600
>> -86.978400 1111.000    0,33.637800 -86.957300 1111.000    0,33.635900
>> -86.946700 1111.000    0,33.640900 -86.923400 1111.000    0,33.639000
>> -86.912900 1111.000    0,33.635300 -86.891800 1111.000    0,33.633400
>> -86.881300 1111.000    0,33.620800 -86.862400 1111.000    0,33.617000
>> -86.841400 1111.000    0,33.615100 -86.830800 1111.000    0,33.611300
>> -86.809800 1111.000    0,33.607500 -86.788700 1111.000    0,33.605600
>> -86.778200 1111.000    0,33.601800 -86.757100 1111.000    0,33.606800
>> -86.733800 1111.000    0,33.604900 -86.723200 1111.000    0,33.611800
>> -86.710400 1111.000    0,33.618700 -86.697600 1111.000    0,33.625600
>> -86.684800 1111.000    0,33.632500 -86.672000 1111.000    0,33.641300
>> -86.669700 1111.000    0,33.658900 -86.665100 1111.000    0,33.667700
>> -86.662800 1111.000    0,33.678400 -86.671100 1111.000    0,33.689200
>> -86.679400 1111.000    0,33.699900 -86.687600 1111.000    0,33.701800
>> -86.698200 1111.000    0,33.705600 -86.719200 1111.000    0,33.718200
>> -86.738000 1111.000    0,33.720100 -86.748600 1111.000    0,33.715100
>> -86.772000 1111.000    0,33.718900 -86.793000 1111.000    0,33.720800
>> -86.803600 1111.000    0,33.724600 -86.824700 1111.000    0,33.719600
>> -86.848100 1111.000    0,33.721500 -86.858600 1111.000    0,33.725300
>> -86.879700 1111.000    0,33.727200 -86.890200 1111.000    0,33.731000
>> -86.911300 1111.000    0,33.732900 -86.921900 1111.000    0,33.745500
>> -86.940700 1111.000    0,33.747400 -86.951300 1111.000    0,33.751100
>> -86.972400 1111.000    0,33.754900 -86.993500 1111.000    0,33.765600
>> -87.001800 1111.000    0,33.769400 -87.022900 1111.000    0,33.762400
>> -87.035700 1111.000    0,33.764300 -87.046300 1111.000    0,33.757400
>> -87.059100 1111.000    0,33.759200 -87.069700 1111.000    0,33.752300
>> -87.082500 1111.000    0,33.745400 -87.095300 1111.000    0))', 
>> 4326));
>>
>>
>>
>
>
>
>
>
>
> Elwood Cordery
> Rockwell Collins
> Contract Software Engineer
> 319-295-8248
>
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