Hello there Jody Unfortunately, I don't really have resources right now to study and implement complex projection computations, if that's what you meant.. :P
Anyway, what I was really after was a confirmation (I guess we could say that it is confirmed) that there is no good globally valid equal area projection available in GeoTools. Given what you guys discuss here (http://www.mail-archive.com/[email protected]/msg20717.html) no support for Mollweide exists or will be implemented in the short-term. I am assuming that support for Sinusoidal goes the same way. I am just a little surprised because it seems that OpenLayers does support Mollweide, Sinusoidal, etc, because they are all available in proj4js. See this link: http://www.equal-area-maps.com/ (by the way, proj4js seems to consider Mollweide to be EPSG:54009 and Sinusoidal to be EPSG:54008, but they are not present in GeoTools' EPSG library) On the other hand, my issue right here is just to *compute the area* of a feature; I don't need to render it. So if the Albers Conical Equal Area projection holds its "equal area" properties for the entire world, that's fine for me. Do you know if that's true?? I actually did a little test using a shapefile with Brazil's states, which includes a computed area for each state as an attribute (although I have no idea where those computed areas came from). I used the Canada-BC parameters (EPSG:3005) and then the Florida parameters (EPSG:3086), and the areas computed were almost identical and both pretty reasonable (less than 0.4% of error compared to the pre-computed values). I still need to see if it gets better if I adjust the parameters for each state. I also still do not know if I could use this to compute the area of polar regions (e.g., Antarctica) Cheers Milton Jody Garnett wrote: > Hi Milton; > > A month or so ago we went over how to generate an equal area projection > (either generate the WKT using Albers Conic; or do something similar > programatically). There are a number of "AUTO" projections defined in > GeoTools (they take the form "AUTO:<CODE>,<lat>,<lon>"). But I am not aware > if any of them are equal area ... perhaps you could look. > > People do donate additional projections; perhaps you would be interested in > donating one of the ones you mention? > The documentation and the use of BC Albers in examples is mostly my fault as > that is where I was working. > > Let us know how you go; I think an "AUTO" projection that used Albers Conic > would be great. > > Jody > > On 14/07/2010, at 1:41 AM, Milton Jonathan wrote: > >> Hello >> >> We have a simple issue down here: we want to compute the area of an >> arbitrary polygonal feature. >> >> The straightforward way I thought about was to simply convert that >> geometry to an equal-area projection, and then let JTS Geometry.getArea >> do the rest. >> >> However... I was surprised that I couldn't find a single equal-area >> projection in GeoTools that is available globally (say the user wants to >> compute the area of Russia, or of Antarctica). From what I saw, >> something like the Mollweide or Sinusoidal projections would do the job, >> but they don't seem to be currently implemented in GeoTools. >> >> Going around the documentation, e-mail lists, etc. my impression is that >> the only available equal-area projection is the Albers Conic Equal-Area. >> However, it's not clear to me how I should play around with the standard >> parallel parameters (ok, would need to study it a little), but more than >> the that I'm really not sure how this would behave for features that >> cross the equator. >> >> Any help appreciated! >> >> Cheers >> Milton >> >> -- >> >> Milton Jonathan >> Grupo GIS e Meio Ambiente >> Tecgraf/PUC-Rio >> Tel: +55-21-3527-2502 >> >> ------------------------------------------------------------------------------ >> This SF.net email is sponsored by Sprint >> What will you do first with EVO, the first 4G phone? >> Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first >> _______________________________________________ >> Geotools-gt2-users mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users > > -- Milton Jonathan Grupo GIS e Meio Ambiente Tecgraf/PUC-Rio Tel: +55-21-3527-2502 ------------------------------------------------------------------------------ This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
