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<DIV><FONT face=Arial size=2>Silke,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I'm probably not the best person to answer this,
but I think the reason for your polygon disappearing is that you're using 8bit
png, which is indexed colour. When the map is rendered, each pixel is assigned a
colour closest to what the colour table is filled up with. If your polygon is
black, and its width is less than half a pixel, it is likely not to show up
(because the majority of the invididual pixels consist of the surrounding
colour, which is picked instead). The colour for that pixel will be whatever
surrounds the polygon. It will not 'interpolate' the colour (make it grey,
anti-aliased), like 24bit real-colour would.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>If you think that is not the case, maybe check
your file's geometry. I have seen (parts of) polygons disappear if the geometry
wasn't valid, e.g. if a shapefile was imported from CAD, which allows unclosed
polygons.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>regards,</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Jacob</FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>-----Original Message-----<BR>From: UMN MapServer
Users List [mailto:MAPSERVER-USERS@LISTS.UMN.EDU] On Behalf Of Silke
Reimer<BR>Sent: 26 July 2005 01:02<BR>To: <A
href="mailto:MAPSERVER-USERS@LISTS.UMN.EDU">MAPSERVER-USERS@LISTS.UMN.EDU</A><BR>Subject:
[UMN_MAPSERVER-USERS] Holes in polygons in some scales</FONT></DIV>
<DIV> </DIV><FONT face=Arial size=2>
<DIV><BR>Hallo!</DIV>
<DIV> </DIV>
<DIV>I have a question concerning map rendering. Let me first describe
the<BR>effect that I observed:</DIV>
<DIV> </DIV>
<DIV>If you have a look at [1] you see a part of map with a street going<BR>from
southwest to northeast which is correctly shown as kind of a<BR>line.</DIV>
<DIV> </DIV>
<DIV>On [2] you see the same street on a smaller scale. Now the line is<BR>shown
with some gaps inbetween which - in my opinion - shouldn't<BR>happen.</DIV>
<DIV> </DIV>
<DIV>First I thought that this happens because the road is defined as a
very<BR>narrow polygon which becomes too small in some scales to
be<BR>considered for rendering. So I changed the layers type from polygon<BR>to
line. According to my theory the full outline of the polygon<BR>should be drawn.
But the gaps still remained.</DIV>
<DIV> </DIV>
<DIV>Now my questions: Do you have any idea what happens here? And do
you<BR>know how to avoid this effect by using a special configuration in<BR>the
mapfile?</DIV>
<DIV> </DIV>
<DIV>Many thanks for your help,</DIV>
<DIV> </DIV>
<DIV> Silke</DIV>
<DIV> </DIV>
<DIV><BR>[1] <A
href="http://ftp.intevation.de/users/silke/mapserver/polywithoutholes.png">http://ftp.intevation.de/users/silke/mapserver/polywithoutholes.png</A></DIV>
<DIV> </DIV>
<DIV>[2] <A
href="http://ftp.intevation.de/users/silke/mapserver/polywithholes.png">http://ftp.intevation.de/users/silke/mapserver/polywithholes.png</A></DIV>
<DIV> </DIV>
<DIV><BR>-- <BR>Intevation GmbH</DIV>
<DIV> </DIV>
<DIV>Georgstrasse
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href="http://intevation.de">http://intevation.de</A>
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href="http://intevation.de/~silke">http://intevation.de/~silke</A><BR>FreeGIS.org
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href="http://freegis.org/">http://freegis.org/</A><BR></FONT></DIV></BODY></HTML>