Dear Mike, please, read below....
Regards, Simone Giannecchini == Meet us at GEO Business 2014! in London! Visit http://goo.gl/fES3aK for more information. == Ing. Simone Giannecchini @simogeo Founder/Director GeoSolutions S.A.S. Via Poggio alle Viti 1187 55054 Massarosa (LU) Italy phone: +39 0584 962313 fax: +39 0584 1660272 mob: +39 333 8128928 http://www.geo-solutions.it http://twitter.com/geosolutions_it ------------------------------------------------------- On Mon, Apr 28, 2014 at 10:25 PM, Mike Grogan <[email protected]> wrote: > Simone, > > As you might can tell from some of my recent posts, I am a meteorologist > focused primarily on meteorological data systems, so I am glad to see your > ongoing focus in that area. Particularly, I was excited to see details > about wind barbs on your blog: > > http://www.geo-solutions.it/blog/developers-corner-supporting-wind-barbs-geoserver-geotools/ > > and I have been working with the RasterAsPointCollection transformation for > some time as shown here: > > http://geoserver.geo-solutions.it/edu/en/wps/rendering_tx.html#point-extraction > > I do want to raise one concern and/or question about the "Rotation" angle > for the Mark used to symbolize the vector. > > From a scientific perspective, we want the arrow or vector to point TOWARD > the direction wind is blowing, right, and conversely the barb to point in > the direction FROM which the wind is blowing. This is something we are going to take into account for the work we are doing. It is going to be available tomorrow, but let's say before the end of May it should be available at least on Master. > > However, doesn't the ROTATION parameter for the mark (arrow, barb, etc.) > only impact rotation of the mark within screen coordinates? In other words, > doesn't it just rotate a mark by a certain angle on the screen, without > respect to the underlying map projection? > > If so, then the arrows or barbs displayed would only be valid for maps with > a Mercator projection, where true north aligns with "up" on the > screen/map/grid. > > For many other projections, though, "up" on the screen/map/grid does not > align with true north. In fact, depending on the projection and location, > "up" may be toward the south! > > So, again as a question and comment ... is ROTATION relative to the screen > or to the underlying map rotation? To get the vector to be properly rotated > with respect to true north and underlying land masses (and not screen "up"), > it would need to be relative to the underlying projection, not the screen. > > I am currently working on this aspect myself ... and am finding myself > needing to calculate the Grid Convergence Angle at each point ... where I > will be able to know how far off the "up" axis at that point is from true > north. I will then have to account for that angle and add it to / subtract > it from the screen ROTATION angle so that my vectors truly show actual > direction when I am using a non-mercator basemap. I had a separate GeoTools > post asking the best way to calculate Grid Convergence Angle ... and I am > still working on that. > > Does this make sense or are you already compensating for any underlying map > projection which might rotate "up" away from true north? If so, do you mind > sharing how you are accomplishing that? The idea is to create a specific filter function to complement the rotation depending on the target project. It is not super easy but if you are interested in helping out we can share some additional details with you, let us know... > > Thanks again! > > - Mike Grogan ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available. Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Geoserver-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geoserver-users
