[Mapserver-users] ECW not showing below certain scale

[Yewondwossen Assefa]

I have put a new version of mapserver 4.3 (current CVS) build with GDAL 
1.2.1 at 
http://www.maptools.org/php_mapscript/index.phtml?page=downloads.html 
(llok at the end of the page for the developpment verion). Let me know 
if it solves the ECW issue.

Later,

Frank Warmerdam wrote:

> Delfos, Jacob wrote:
> 
>> Hi All,
>>
>> I've been running into a little problem with mapserver 4.2, which I 
>> was also experiencing in Chameleon 1.99; when I zoom in quite far on 
>> the map (holding an ecw image), the map doesn't show up. It keeps 
>> trying to load, but nothing comes, suggesting it got stuck somewhere. 
>> CPU activity is initially at maximum for a few seconds (as normal when 
>> loading the map) but then drops while the map doesn't show (I'm 
>> loading the map in the browser on the server itself). The mapserv 
>> process won't allow itself to get killed either.
>>
>> If I simply replace my mapserv.exe file with one of version 4.0, the 
>> problem is gone. Of course the map takes quite a few seconds to show, 
>> which is normal when zooming close on an ECW, but it does show.
>>
>> I've tried this quite a few times in different browsers, but the map 
>> never shows at that scale when the ECW is in there. I have tried 
>> different mapfiles with different ECW's as well. Has the mechanism to 
>> display the ECW changed? It seems that as soon as I reach a resolution 
>> where I go beyond the ECW resolution (1pixel:1pixel) it dies.
> 
> 
> Jacob,
> 
> I was able to reproduce a problem with ECW supersampling when assertions
> are turned on in GDAL 1.2.0.  I have just issued a GDAL 1.2.1 with this 
> issue
> fixed, and suggested to Assefa that he upgrade to that as time permits.
> 
> I am not absolutely positive if that is your problem or not.
> 
> I suspect you are seeing differences between MapServer 4.0 and 4.2 because
> MapServer 4.2 tries to use "dataset" level io calls when available.  This
> allows reading red, green and blue in one pass against ECW for instance,
> resulting in better performance.  However, it uses different code paths
> which may have different issues.
> 
> So ... if and when new binaries are available with GDAL 1.2.1 I would
> suggest you try MapServer 4.2 again.  In the meantime you could just set an
> appropriate MINSCALE so the ECW would stop rendering when supersampled,
> or switch back to the build that works.
> 
> Finally, I will once again strongly suggest that folks running into 
> problems
> like this try and reproduce it at the commandline with shp2img and 
> appropriate
> extent and debug options.  This often results in much more meaningful error
> messages than you get on in a web application.
> 
> Best regards,


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Assefa Yewondwossen
Software Analyst

Email: assefa at dmsolutions.ca
http://www.dmsolutions.ca/

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925
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