[Portugal] Prj2EPSG

[Hugo Martins]

  Sent to you by Hugo Martins via Google Reader: Prj2EPSG via OpenGeo by
Paul Ramsey on 6/14/10

Once upon a time, a group of smart people got together to define a
common standards base for geographic map services, a “Web Map Service”
specification, if you will.

They wanted their map services to be interoperable, but different maps
can be rendered using different projections, and in order to overlay
one map onto another, they needed to know (and advertise) the
projections of both.

There was an existing standard for representing map projections, called
“well-known text” (which is also, confusingly, the name that describes
a standard for representing geometries) but it was quite verbose. Who,
after all, could remember this:

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"]]

More importantly, how would this fit cleanly into a URL?

Fortunately, there already existed a large database of commonly used
map projections: the EPSG database. 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.

But, unlike me, most GIS practitioners haven’t memorized the EPSG
database. So they frequently ask questions like “what is the EPSG
number for Oregon State-Plane South?” and “how do I find the EPSG
number for this shapefile?” One could search spatialreference.org, 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:

SELECT srid, srtext FROM spatial_ref_sys WHERE srtext ILIKE '%oregon%';

But today, I can provide a much simpler answer: Use prj2epsg.org. With
prj2epsg.org, you can paste in full well-known text descriptions, you
can type in shorter keyword searches, and you can even read a .prj file
directly.

This free public service is provided by OpenGeo and our cloud services
provider SkyGone. The code is naturally all open source and the service
is built on top of the same GeoTools library that is at the heart of
our OpenGeo Suite.

And now we’re all hopefully one step closer to living happily ever
after.

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