<div style="margin: 0px 2px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="margin: 0px 1px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="padding: 4px; background-color: #c3d9ff;"><h3 style="margin:0px 3px;font-family:sans-serif">Sent to you by Hugo Martins via Google Reader:</h3></div>
<div style="margin: 0px 1px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="margin: 0px 2px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="font-family:sans-serif;overflow:auto;width:100%;margin: 0px 10px"><h2 style="margin: 0.25em 0 0 0"><div class=""><a href="http://blog.opengeo.org/2010/06/14/prj2epsg/">Prj2EPSG</a></div></h2>
<div style="margin-bottom: 0.5em">via <a href="http://blog.opengeo.org" class="f">OpenGeo</a> by Paul Ramsey on 6/14/10</div><br style="display:none">
<p>Once upon a time, a group of smart people got together to define a common standards base for geographic map services, a “<a href="http://www.opengeospatial.org/standards/wms">Web Map Service</a>” specification, if you will.</p>
<p>They wanted their map services to be interoperable, but different maps can be rendered using different <a href="http://en.wikipedia.org/wiki/Map_projection">projections</a>, and in order to overlay one map onto another, they needed to know (and advertise) the projections of both.</p>
<p>There was an existing standard for representing map projections, called “<a href="http://en.wikipedia.org/wiki/Well-known_text#Spatial_reference_systems">well-known text</a>” (which is also, confusingly, the name that describes a standard for representing geometries) but it was quite verbose. Who, after all, could remember this:</p>
<pre>GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,
AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0,
AUTHORITY["EPSG","8901"]],
UNIT["degree",0.01745329251994328,
AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4326"]]</pre>
<p>More importantly, how would this fit cleanly into a URL?</p>
<p>Fortunately, there already existed a large database of commonly used map projections: the <a href="http://www.epsg.org/CurrentDB.html">EPSG database</a>. This provided a single numeric ID for each common map projection. So it was decided that all map services must advertise their projection using a unique number defined by an authority, and set EPSG as the first authority. And so ESPG:4326 came into the world (WGS84 geographic coordinates) along with ESPG:26910 (NAD83 UTM Zone 10 North), and many others.</p>
<p>But, unlike me, most GIS practitioners haven’t memorized the EPSG database. So they frequently ask questions like <em>“what is the EPSG number for Oregon State-Plane South?”</em> and <em>“how do I find the EPSG number for this shapefile?”</em> One could search <a href="http://spatialreference.org">spatialreference.org</a>, a site for understanding spatial reference systems. My own answer used to be a fairly unhelpful set of directions for doing a text search of the PostGIS SPATIAL_REF_SYS table:</p>
<pre>SELECT srid, srtext FROM spatial_ref_sys WHERE srtext ILIKE '%oregon%';</pre>
<p>But today, I can provide a much simpler answer: <strong>Use <a href="http://prj2epsg.org/search">prj2epsg.org</a></strong>. With <strong><a href="http://prj2epsg.org/search">prj2epsg.org</a></strong>, you can paste in <a href="http://prj2epsg.org/search?terms=PROJCS%5B%22NAD_1983_StatePlane_Oregon_South_FIPS_3602_Feet_Intl%22%2CGEOGCS%5B%22GCS_North_American_1983%22%2CDATUM%5B%22D_North_American_1983%22%2CSPHEROID%5B%22GRS_1980%22%2C6378137.0%2C298.257222101%5D%5D%2CPRIMEM%5B%22Greenwich%22%2C0.0%5D%2CUNIT%5B%22Degree%22%2C0.0174532925199433%5D%5D%2CPROJECTION%5B%22Lambert_Conformal_Conic%22%5D%2CPARAMETER%5B%22False_Easting%22%2C4921259.842519685%5D%2CPARAMETER%5B%22False_Northing%22%2C0.0%5D%2CPARAMETER%5B%22Central_Meridian%22%2C-120.5%5D%2CPARAMETER%5B%22Standard_Parallel_1%22%2C42.33333333333334%5D%2CPARAMETER%5B%22Standard_Parallel_2%22%2C44.0%5D%2CPARAMETER%5B%22Latitude_Of_Origin%22%2C41.66666666666666%5D%2CUNIT%5B%22Foot%22%2C0.3048%5D%5D">full well-known text descriptions</a>, you can type in <a href="http://prj2epsg.org/search?terms=bc+albers">shorter keyword searches</a>, and you can even read a .prj file directly.</p>
<p>This free public service is provided by <a href="http://opengeo.org">OpenGeo</a> and our cloud services provider <a href="http://www.skygoneinc.com/">SkyGone</a>. The code is naturally all <a href="http://svn.opengeo.org/prj2epsg/trunk/">open source</a> and the service is built on top of the same <a href="http://geotools.org"></a>GeoTools library that is at the heart of our <a href="http://opengeo.org/products/suite">OpenGeo Suite</a>.</p>
<p>And now we’re all hopefully one step closer to living happily ever after.</p></div>
<br>
<div style="margin: 0px 2px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="margin: 0px 1px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="padding: 4px; background-color: #c3d9ff;"><h3 style="margin:0px 3px;font-family:sans-serif">Things you can do from here:</h3>
<ul style="font-family:sans-serif"><li><a href="http://www.google.com/reader/view/feed%2Fhttp%3A%2F%2Fblog.opengeo.org%2Ffeed%2F?source=email">Subscribe to OpenGeo</a> using <b>Google Reader</b></li>
<li><a href="http://www.google.com/reader/?source=email">Get started using Google Reader</a> to easily keep up with <b>all your favorite sites</b></li></ul></div>
<div style="margin: 0px 1px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>
<div style="margin: 0px 2px; padding-top: 1px; background-color: #c3d9ff; font-size: 1px !important; line-height: 0px !important;"> </div>