Paulius, I referred to Nicolas Ribot's answer to your question on how to get the area. He suggested to do the transform to UTM 40N (which has a SRID = 32640, see his statement). This was likely because he thought your data was somewhere in the United Arab Emirates, due to the swap in lat, lon.
UTM 35N has SRID = 32635 Hope this solves the puzzle, Guido >-- Original Message -- >Date: Wed, 12 Mar 2008 09:52:35 -0700 (PDT) >From: Paulius J <[EMAIL PROTECTED]> >To: [email protected] >Subject: Re: [postgis-users] Postgis Area size problem >Reply-To: PostGIS Users Discussion <[email protected]> > > > >Hello, GL, > >Thanks, for your post. The first part of the problem is easy and at last >I >got the query working :) While I have some questions about the second: >'- You should use UTM zone 35N, which is the one for Lithuania'. Here as >I >understand you are talking about SRID`s? If yes, so is it a difference which >SRID I am using (I use the database only to save points or group of points >from GPS and Google Maps? In database I only want to save the lat and lon >from GPS device or Google Maps on the global scope, so which SRID should >I >use, or there is no difference in my situation? The boundaries of Lithuania >is only an example because I live here. > > >P.S. sorry for such a question but I am new in this. > >Paulius J > >Guido Lemoine wrote: >> >> PJ, >> >> I guess your dealing with Lithuania data. Your problem is twofold: >> >> - You have lat and lon in the wrong order >> - You should use UTM zone 35N, which is the one for Lithuania >> >> Hence, do the following: >> >> select st_area(st_transform(geometryFromText('POLYGON((21.06079 56.05364 >> ,22.12646 56.43213 ,24.55444 56.27386 ,24.88403 56.41998 >> ,25.10376 56.17002 ,26.63086 55.6528 ,26.25732 54.965 ,25.75195 54.78168 >> ,25.62012 54.31652 ,25.74097 54.14957 ,25.53223 54.18173 ,25.47729 >> 54.28447 >> ,24.37866 53.90434 ,23.47778 53.96255 ,23.20313 54.25881 ,22.77466 >> 54.35496 >> ,22.82959 54.78802 ,22.65381 54.95239 ,21.32446 55.26034 ,21.0498 56.0475 >> ,21.06079 56.05364 ))', 4326), 32635)); >> >> --> 64039242950.5568 (sqm) >> >> GL >> >> Paulius J wrote: >>> Thank you for your quick reply Nicolas, >>> >>> Now I get the results which are more likely to be the truth, but they >>> differ >>> from reality quiet a lot. >>> Maybe it can be a problem that I got these coordinates from Google Maps? >>> If >>> I am correct, the polygon which I posted as example should be about 64 >>> 000 >>> square kilometers. >>> >>> Paulius J >>> >>> >>> Nicolas Ribot wrote: >>> >>>> On 11/03/2008, Paulius J <[EMAIL PROTECTED]> wrote: >>>> >>>>> Hello, >>>>> >>>>> I have such a problem. Here is my polygon and it looks that everthing >>>>> is >>>>> allright: >>>>> POLYGON((56.05364 21.06079,56.43213 22.12646,56.27386 >>>>> 24.55444,56.41998 >>>>> 24.88403,56.17002 25.10376,55.6528 26.63086,54.965 26.25732,54.78168 >>>>> 25.75195,54.31652 25.62012,54.14957 25.74097,54.18173 >>>>> 25.53223,54.28447 >>>>> 25.47729,53.90434 24.37866,53.96255 23.47778,54.25881 >>>>> 23.20313,54.35496 >>>>> 22.77466,54.78802 22.82959,54.95239 22.65381,55.26034 21.32446,56.0475 >>>>> 21.0498,56.05364 21.06079)) >>>>> >>>>> But when i want to find the area of it using Area i get the result: >>>>> 9.04832470074997 >>>>> I do not know how to get the area size in square meters or something >>>>> similar >>>>> to this? Maybe i should use some other function, but according the >>>>> postgis >>>>> manual I use Area or ST_Area and have such problem... >>>>> >>>>> P.S. i am using SRID = 4326 for the Geometry column. >>>>> >>>>> >>>> ST_area computes the area in geometry's units. Here square degrees. >>>> Repreject your data in a metric reference system (like UTM for >>>> instance) with st_transform(), then compute the area. >>>> >>>> Something like: >>>> >>>> select st_area(st_transform(geometryFromText('POLYGON((56.05364 >>>> 21.06079,56.43213 22.12646,56.27386 24.55444,56.41998 >>>> 24.88403,56.17002 25.10376,55.6528 26.63086,54.965 26.25732,54.78168 >>>> 25.75195,54.31652 25.62012,54.14957 25.74097,54.18173 25.53223,54.28447 >>>> 25.47729,53.90434 24.37866,53.96255 23.47778,54.25881 23.20313,54.35496 >>>> 22.77466,54.78802 22.82959,54.95239 22.65381,55.26034 21.32446,56.0475 >>>> 21.0498,56.05364 21.06079))', 4326), 32640)); >>>> >>>> Nico >>>> _______________________________________________ >>>> postgis-users mailing list >>>> [email protected] >>>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>>> >>>> >>>> >>> >>> >> >> -- >> ---------------------------------------------------------------- >> Guido Lemoine >> Joint Research Centre, European Commission >> Institute for the Protection and Security of the Citizen (IPSC) >> Support to External Security >> Via E. Fermi, 2749 TP 267 Ispra 21027 (VA), Italy >> Tel. +39 0332 786239 (direct line) Fax. +39 0332 785154 >> WWW: http://ses.jrc.it >> ---------------------------------------------------------------- >> Disclaimer: >> Views expressed are those of the individual and do not represent >> the views of the European Commission >> >> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users >> >> > >-- >View this message in context: >http://www.nabble.com/Postgis-Area-size-problem-tp15988337p16008014.html >Sent from the PostGIS - User mailing list archive at Nabble.com. > >_______________________________________________ >postgis-users mailing list >[email protected] >http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
