Donut Symbol.

[Steve Lime]

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
>>
>>    
>>
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