I did it once when implementing an "auto" projection for WMS support (see
org.geotools.referencing.crs.AUTOCRSAuthorityFactory.AUTO42004) . But the
real thing is here rather than looking up a formal definition using
CRS.decode("EPSG:3005") ... you would be wither generating some WKT and then
parsing it; or making use of the referencing module factories to construct
the object you want an element at a time.
The user guide has some examples:
- http://docs.codehaus.org/display/GEOTDOC/03+CoordinateReferenceSystem
But as to the specifics of what you want to generate; lets look at the WKT
definition of an equal area projection together and see what can be figured
out - here is the definition of 3005... grabbed out of uDig 1.1.1 (which
uses the older epsg-properties module).
PROJCS["NAD83 / BC Albers",
GEOGCS["NAD83",
DATUM["North_American_Datum_1983",
SPHEROID["GRS 1980", 6378137.0, 298.257222101,
AUTHORITY["EPSG","7019"]],
TOWGS84[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],
AUTHORITY["EPSG","6269"]],
PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],
UNIT["degree", 0.017453292519943295],
AXIS["Lon", EAST],
AXIS["Lat", NORTH],
AUTHORITY["EPSG","4269"]],
PROJECTION["Albers_Conic_Equal_Area"],
PARAMETER["central_meridian", -126.0],
PARAMETER["latitude_of_origin", 45.0],
PARAMETER["standard_parallel_1", 50.0],
PARAMETER["false_easting", 1000000.0],
PARAMETER["false_northing", 0.0],
PARAMETER["standard_parallel_2", 58.5],
UNIT["m", 1.0],
AXIS["x", EAST],
AXIS["y", NORTH],
AUTHORITY["EPSG","3005"]]
So you can see the axis are in meters which is good; the projection is an
albers conic equal area which is what we want; I would start fiddling with
the central meridian and latitude of origion to line this thing up with your
data. I would consider using udig; or your own view to visualize what is
going on as you change the values; and once you understand what they do you
can write some java code to reproduce your result.
Jody
On Fri, Feb 13, 2009 at 1:58 PM, Davis Ford <[email protected]>wrote:
> Thank you Jody -- I appreciate the answer.
>
> I'd be interested in figuring out how to generate a CRS on the fly. I
> will investigate this more. Any pointers / tips / references are
> greatly appreciated.
>
> Final quick question: is there a general projected CRS that would work
> for North America? I am still learning all the different EPSG.
> http://spatialreference.org/ is great. For instance, I am using
> EPSG:2807 and it does what I want if I insert that in the code I
> pasted, because my point is in Michigan, but I am wondering if there
> is one that would work (albeit with less accuracy) for North America
> in general.
>
> Regards,
> Davis
>
> On Thu, Feb 12, 2009 at 5:54 PM, Jody Garnett <[email protected]>
> wrote:
> > I am going to try and quickly answer; but you will need others to fill in
> > the details:
> > - I often know a good equal area projection for the area I will be
> working
> > in (EPSG:3005 bc albers is a good CRS for working in western canada for
> > example).
> > - you could study how bc albers is defined and make yourself a
> > CoordinateReferenceSystem on the fly for the specific point you are
> > interested in
> >
> > Once you have the point in an equal area projection you can use buffer to
> > get a polygon; and then transform this polygon back to the google
> projection
> > if you like (it will show up as an ellipse).
> >
> > Jody
> >
> > Davis Ford wrote:
> >>
> >> Hi, I have a simple point obtained from Google Earth and I want to
> >> calculate a buffer around this in units of miles. So, I think the
> >> general pattern is like this:
> >>
> >> Geometry source= new WKTReader().read("POINT(-82.90755596903085
> >> 42.40409951227155)");
> >> CoordinateReferenceSystem sourceCRS = CRS.decode("EPSG:4326");
> >> // what should I project it to?
> >> CoordinateReferenceSystem targetCRS = CRS.decode("???????");
> >> MathTransform transform = CRS.findMathTransform(sourceCRS, targetCRS,
> >> true);
> >>
> >> Geometry target = JTS.transform(source, transform);
> >>
> >> // buffer by 1 mile (meters)
> >> Geometry buffer = target.buffer(1609.344);
> >>
> >> // re-project
> >> transform = CRS.findMathTransform(targetCRS, sourceCRS, true);
> >> Geometry geometry = JTS.transform(buffer, transform);
> >>
> >> I'm not exactly sure what CRS I should project it to. If I know
> >> exactly in the world where this is I could use that, but is there a
> >> general EPSG that I can use where the units of distance are in meters,
> >> so I can use the JTS buffer method correctly?
> >>
> >> Also, I read on the Wiki that Google is not really WGS84 -- will this
> >> cause issues or should I try to use the CRS posted on the Wiki to get
> >> more accurate results:
> >>
> >> http://docs.codehaus.org/display/GEOTDOC/08+Google+Maps+Projection
> >>
> >> Thanks in advance,
> >> Davis
> >>
> >>
> >>
> ------------------------------------------------------------------------------
> >> _______________________________________________
> >> Geotools-gt2-users mailing list
> >> [email protected]
> >> https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
> >>
> >
> >
>
>
>
> --
> Zeno Consulting, Inc.
> home: http://www.zenoconsulting.biz
> blog: http://zenoconsulting.wikidot.com
> p: 248.894.4922
> f: 313.884.2977
>
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