RE: [Geotools-gt2-users] polygons with holes in them

[Combe, C. <C....@na...>]

sorry, that "thing" I mentioned at the end of my last mail is obviously
called a RenderedMapScale,
col


-----Original Message-----
From: Combe, Colin
To: 'geo...@li...'
Sent: 8/27/03 9:57 PM
Subject: [Geotools-gt2-users] polygons with holes in them

Hi,=20
I'm making progress with gt2 but am having problems displaying polygons
with
holes in them. For example, if I load the following gml data into
MapViewer2
(edited to take a GMLDataSource):

 =20
<gml:featureCollection xmlns:gml=3D"http://www.opengis.net/gml">=20
   <gml:FeatureMember>=20
    <gml:Polygon>=20
     <gml:outerBoundaryIs>=20
      <gml:LinearRing>=20
       <gml:coordinates decimal=3D"." cs=3D"," ts=3D" ">=20
          0.0,0.0 100.0,0.0 100.0,100.0 0.0,100.0 0.0,0.0=20
       </gml:coordinates>=20
      </gml:LinearRing>=20
     </gml:outerBoundaryIs>=20
     <gml:innerBoundaryIs>=20
      <gml:LinearRing>=20
        <gml:coordinates decimal=3D"." cs=3D"," ts=3D" ">=20
          10.0,10.0 10.0,40.0 40.0,40.0 40.0,10.0 10.0,10.0=20
        </gml:coordinates>=20
      </gml:LinearRing>=20
     </gml:innerBoundaryIs>=20
    </gml:Polygon>=20
   </gml:FeatureMember>=20
</gml:featureCollection>=20

I thought I should see a polygon with a hole in it, but both the =
squares
are
filled in. I can't seem to find anything in the documentation about
enabling
clipping or anything, but i noticed that PolygonTest.java for the
renderer
package does display such a polygon.=20

There's a couple of other things that are confusing me. When I read in
my
shapfiles there were problems (ArithmeticException: No convergence for
points * and *) with some points in lineStrings. I worked round this by
outputing the files as GML and then commenting out the offending =
points.
After a quick look at the source code, i was confused about how 2 =
points
could be non-equal but it not to be possible to calculate the distance
between them, i couldn't see how it could reach the line that throws =
the
exception (org.geotools.cs.Ellipsoid.orthodromicDistance
(Ellipsoid.java:382)). For example, if the commenting is removed from:

<gml:LineString>=20
        <gml:coordinates decimal=3D"." cs=3D"," ts=3D" ">=20
330000,674826 330134,674686 330154,674668  <!--330176,674640-->
330358,674457 330410,674389                   =20
        </gml:coordinates>=20
</gml:LineString>=20

it causes the error: No convergence for points 330176=B000.0'E
674640=B000.0'N
and 330358=B000.0'E 674457=B000.0'N. I guess this is some subtlety to =
do
with
map projections that i don't know about...

The other thing thats confusing me is the scale bar down in the bottom
left
of MapViewer2. Its a nice feature but its readings are wrong and don't
seem
to change in a sensible way as you zoom in and out. I expect this is
probably because it not finished but I can't find anything in the docs
about
what this thing is called or how to control it.=20

I couldn't get MapViewer to work (just displays a blank canvas/map =
pane)
but
i'm well impressed by MapViewer2 - IMHO its nicer than the demos that
come
with ESRI's Java Map Objects (the evaluation copy of it anyway).=20

thanks for your help - and the huge amount of work thats gone into this
toolkit :)=20
colin=20



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