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 ------------------------------------------------------------------------------ Open Source Business Conference (OSBC), March 24-25, 2009, San Francisco, CA -OSBC tackles the biggest issue in open source: Open Sourcing the Enterprise -Strategies to boost innovation and cut costs with open source participation -Receive a $600 discount off the registration fee with the source code: SFAD http://p.sf.net/sfu/XcvMzF8H _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
