<HTML>
<HEAD>
<TITLE>Re: [UMN_MAPSERVER-USERS] Reprojected ghost images</TITLE>
</HEAD>
<BODY>
<FONT FACE="Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12.0px'>John -<BR>
<BR>
The GB National Grid is a Transverse Mercator projection with a central parallel of 49 degrees North. A world map in that projection would look rather strange, but should be possible (if inadvisable). I realize you’re using a latitude/longitude output projection (equally inadvisable, but that’s another soapbox) but when you put your NG layer on that output map you’re in effect causing a world-sized view of your TM projection in order to figure out where your TM source image should be placed.<BR>
<BR>
I’m not quite seeing how your particular symptom is produced by that problem, however. Is your map viewer publicly accessible, and can you post your map file? Thanks.<BR>
<BR>
- Ed<BR>
<BR>
-- <BR>
Ed McNierney<BR>
President and Chief Mapmaker<BR>
Maps a la carte, Inc. / TopoZone.com<BR>
73 Princeton Street, Suite 305<BR>
North Chelmsford, MA 01863<BR>
Phone: (978) 251-4242<BR>
Fax: (978) 251-1396<BR>
ed@topozone.com<BR>
<BR>
<HR ALIGN=CENTER SIZE="3" WIDTH="95%"><B>From: </B>John Westwood <John.Westwood@PORT.AC.UK><BR>
<B>Reply-To: </B>John Westwood <John.Westwood@PORT.AC.UK><BR>
<B>Date: </B>Fri, 27 Apr 2007 16:43:07 +0100<BR>
<B>To: </B><MAPSERVER-USERS@LISTS.UMN.EDU><BR>
<B>Subject: </B>[UMN_MAPSERVER-USERS] Reprojected ghost images<BR>
<BR>
Hello fellow MapServer users,<BR>
<BR>
I have a small problem with reprojecting a tileindexed raster layer. The original layer is in GB National Grid coordinates and I have reprojected this on the fly to latitude and longitude. The coverage of the layer extends to the area of the United Kingdom. The re-projection works fine and I am very happy with it.<BR>
<BR>
The problem is if I zoom out to a whole World view, there are two duplicates of the reprojected UK raster layer equally spaced on either side of the real layer. The duplicates are on the same line of latitude as the real layer but are approximately located in North America and East Russia. The duplicates are also heavily distorted, and one is the mirror image of the other.<BR>
<BR>
I would like to know what is causing this and how I can possibly prevent it. I have a workaround which is to switch the layer off when I have zoomed out a certain amount; this works ok at the moment but may cause problems in the future. Any ideas would be greatly appreciated. I am using MapServer version 4.10.0-5+etch1 on Debian Etch.<BR>
<BR>
Regards,<BR>
<BR>
John W.<BR>
<BR>
</SPAN></FONT>
</BODY>
</HTML>