Donut Symbol.

[Bill Binko]

Bob,

If your points are stored in PostGIS, there are ways of getting this
perfect.  It's not always pretty, and can require some Nasty SQL, , but
I'd be happy to work with you offline on this (and you can post the
results back to the list).

Bill
bill at binko.net

On Fri, 26 Aug 2005, Blammo wrote:

> Hmm, sounds like overkill for my needs, but it does give me another idea.
> 
> Using Paco's method of a closed "U" shap symbol, I could stack two 
> circle outlines on top of the closed Ushape and use those for the 
> outline colors of the filled donut area.
> 
> It's not pretty, but I won't tell anyone if you don't.
> 
> The sizing of the radius for offset is dynamic and being sent to the 
> sever, so your thoughts are certainly relevent.
> 
> Thanks for the ideas.  I had thought about drawing a PolyShape with a 
> HOLE in it as well.  But this even seemed like overkill.   As a matter 
> of fact, I've probably put to much into it already at this point  :c)
> 
> bobb
> 
> Bill Binko wrote:
> 
> >Another approach is to handle this on the data side: either in Mapscript 
> >or in the database if your data is in PostGIS (and perhaps through OGR: 
> >Frank?)
> >
> >What I do for this is simply have the data set return a buffer() around 
> >the point and then display the layer as a POLYGON rather than a point.
> >
> >So, if your original data was in PostGIS and your DATA line was: 
> >
> >DATA "myPoint from (SELECT oid, myPoint from myTable WHERE someField = 
> >      'someValue') as foo using unique oid using SRID=1234"
> >
> >You could just change that to: 
> >
> >DATA "myPoint from (SELECT oid, buffer(myPoint, myRingsize) from myTable 
> >      WHERE someField = 'someValue') as foo using unique oid using SRID=1234"
> >
> >and change your layer from POINT to POLYGON
> >
> >I don't know if OGR can do buffer(), but certainly you could look into it.
> >
> >Bill
> >
> >
> >
> >On Fri, 26 Aug 2005, Steve Lime wrote:
> >
> >  
> >
> >>A dynamic donut is not possible given the way MapServer currently works.
> >>
> >>The way point symbols work is that a raster marker image is rendered based
> >>on the properties of the symbol and a SINGLE style. So this has to be accomplished
> >>within the context of a symbol definition or a style definition. Multiple styles will not
> >>help you because the base circle would already obscure anything underneath it.
> >>
> >>We could change the way an ELLIPSE symbol is rendered so that if you have 
> >>additional second set of radii defined then that defines the hole. But the problem
> >>still remains that you need to specify sizes for the inner and outer ring which would
> >>involve changes to the style object- yuck. 
> >>
> >>One could look at rendering all styles at once as well rather then in turn. You'd just
> >>define the hole somehow as a style. Nice idea but not doable at the moment.
> >>
> >>I wonder if a better approach would be to think about this particular problem as
> >>an exercise in combining a couple of maps. You certainly can use MapServer to build
> >>the base image, and you can also use MapServer to draw the rings in a seperate
> >>images (draw the big ring, and then draw the hole using the background color for
> >>the whole image). You just need to figure out how to combine them.
> >>
> >>You could use DHTML or MapScript to do this. I bet there's a way to do it using straight
> >>CGI (draw the rings as a raster layer in the second map) if we knew more about the
> >>application. For example, you might create the ring image and then refer to it as a
> >>layer in the base image. With AJAX you could do that using the CGI.
> >>
> >>Steve
> >>
> >>    
> >>
> >>>>>Blammo <bob.basques at CI.STPAUL.MN.US> 08/26/05 11:46 AM >>>
> >>>>>          
> >>>>>
> >>Jeff,
> >>
> >>I tried that already.
> >>
> >>What I'm basically after is a sysmbol that is a empty circle with a 
> >>thickness aplied to the line.  Ideally it would be a symbol like 
> >>anyother that I could apply a COLOR and OUTLINECOLOR to.
> >>
> >>Paco's idea of the close "u" shap would work if I didn't need to outline it.
> >>
> >>I also ran into another slight problem as well (may Paco has some ideas 
> >>about this too.)
> >>
> >>I was trying to use this symbol as a distance measuring tool.  but 
> >>seemed to run into a snag with a size limit.   I couldn't get the symbol 
> >>to go over a certain pixel size.   The circle is supposed to represent  
> >>a distance buffer in miles (ground units).
> >>
> >>If I zoom in too close, the symbol won't get any larger than a certain 
> >>size,  about 500 pixels I would guess.   I actually have three of these 
> >>symbols stacked on top of each other for different distances.   But the 
> >>size of the symbol grow as I zoom in, but once I hit this max pixel 
> >>size, the sysbol stop growing at this approx 500 pixel size.
> >>
> >>Thanks
> >>
> >>bobb
> >>
> >>
> >>
> >>Jeff Portwine wrote:
> >>
> >>    
> >>
> >>>I haven't tried this , so it may not work, I've always used filled in 
> >>>shapes.. but couldn't you just use a non-filled in circle:
> >>>
> >>>SYMBOL
> >>> NAME "circle"
> >>> TYPE ellipse
> >>> FILLED false
> >>> POINTS
> >>>   1 1
> >>> END
> >>>END
> >>>
> >>>and then set its size appropriately?   I'm not sure if there is a good way 
> >>>to affect the thickness though, other than stacking several of them with 
> >>>varying sizes.
> >>>
> >>>-Jeff
> >>>
> >>>----- Original Message ----- 
> >>>From: "Bob Basques" <bob.basques at CI.STPAUL.MN.US>
> >>>To: <MAPSERVER-USERS at LISTS.UMN.EDU>
> >>>Sent: Thursday, August 25, 2005 5:39 PM
> >>>Subject: [UMN_MAPSERVER-USERS] Donut Symbol.
> >>>
> >>>
> >>> 
> >>>
> >>>      
> >>>
> >>>>Does anyone know of a good way to make a donut symbol.
> >>>>
> >>>>I need to be able to resize a symbol that is basically a donut.  Where the 
> >>>>donut part is semi-opaque, and the center is open.  It's basically a 
> >>>>min/max distance from a point overlay.  I have the dynamic handing off of 
> >>>>the sizing handled already, but haven't figured out a good way to make a 
> >>>>filled donut symbol.
> >>>>
> >>>>I did mange to make a stacked symbol, but I would really like to have the 
> >>>>center no be filled in, only the area between the MIN/MAX distance from 
> >>>>the point picked.
> >>>>
> >>>>Thanks
> >>>>
> >>>>bobb
> >>>>
> >>>>   
> >>>>
> >>>>        
> >>>>
> >>> 
> >>>
> >>>      
> >>>
> >>    
> >>
> >
> >
> >  
> >
> 
>