Re: [Opengrads-devel] Shapefile extension: first crack

[<efr...@me...>]

Fellows,

Have you guys looked into Geo::Shapelib Perl package for generating POLYGONs?

> My research into the shapefile format led me to conclude that the  
> shaded contour routine in grads will need to be rewritten; Arlindo  
> points out some (not all) of the reasons.  I am working on this for  
> v2.  We also anticipate implementing shapefile support in grads in  
> collaboration with the CPC during 2008... Brian
> 
> On Dec 11, 2007, at 4:47 PM, Arlindo da Silva wrote:
> 
> > Efren,
> >
> >   I am back from vacation. I read quickly the ESRI white paper that
> > describes the shapefile format. What an awkward format! SVG appears a
> > much more elegant approach to vector graphics. In any event, here are
> > my thoughts on how to produce shapefiles from within GrADS:
> >
> > 0) I would produce shapefiles associated with 2D lat-lon "naked
> > plots", that is, those without maps, frames or fonts. Anything else
> > may not make much sense. (Since GrADS draws its own characters, fonts
> > could encoded as polylines but they would be deformed if a map
> > transformation is later applied.)
> >
> > 1) GrADS vector graphics includes both POLYLINES and POLYGON type of
> > shapes. Since one can only have one type of shape per shapefile, a
> > given image (say contour lines on top of shaded contours) would have 2
> > separate shapefiles associated with it: one with POLYGONS, another
> > with POLYLINE objects, for a total of 6 files if you factor in the
> > .shp, .shx and .dbx subfiles. This is ugly.
> >
> > 2) There is an annoying requirement on the enconding of polygons: one
> > must order the vertices so that the "inside" is to the right of the
> > path, something that should have been handled by the renderer.   I
> > believe cairo provides functions to determine whether a point is
> > inside or outside a closed path, so I may be able to use it.
> >
> > 3) Each polygon object would have a single part so as to avoid dealing
> > with similar vertex ordering issues.
> >
> > 4) Now, each POLYLINE or POLYGON object will have a color associated
> > with it. I am hoping one could save the (r,g,b) values in the
> > associated .dbx file, but I am not sure what are the conventions for
> > encoding this.
> >
> > 5) In the case of shaded contours, I am not sure how to encode the
> > color bar (mapping of (r,g,b) into field values).
> >
> >    With all these caveats, would GrADS produced shapefiles still be of
> > any interest? I believe Brian has looked into this as well, I'm cc'ing
> > him as he may not be subscribed to this list.
> >
> > Brian: for reference, here is the thread:
> >
> > http://sourceforge.net/mailarchive/forum.php? 
> > thread_name=77fcd6b20711251803j746a965j689063db5d6e4da8% 
> > 40mail.gmail.com&forum_name=opengrads-devel
> >
> >    Arlindo
> >
> > -- 
> > Arlindo da Silva
> > da...@al...
> 
> 




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