Small differences in input and output

[Benoît Andrieu]

Yep, that worked !
I didn't know that the extents of the mapfile were not the same as the one 
from GDAL. There was my mistake !
So I moved the four corners in order to have the whole extent reduced by one 
pixel and here it was !

I am really thanking you for those fast and accurate answers !!!

Benoît


----- Original Message ----- 
From: "Ed McNierney" <ed at TOPOZONE.COM>
To: <MAPSERVER-USERS at LISTS.UMN.EDU>
Sent: Thursday, June 14, 2007 4:50 PM
Subject: Re: [UMN_MAPSERVER-USERS] Small differences in input and output


> Frank -
>
> For MapServer EXTENT purposes Benoit will need to adjust the extents by 
> one
> whole pixel rather than by half a pixel?  If there are N pixels 
> horizontally
> measured from the center of the left-hand to the center of the right-hand
> pixel, then there are N+1 pixels measured from the left of the left-hand 
> to
> the right of the right-hand pixel, rather than N+0.5.
>
> That is, if you adjust all four corners "in" by 0.5 pixel you'll reduce 
> the
> height and width by 1 whole pixel each.
>
>     - Ed
>
> -- 
> Ed McNierney
> President and Chief Mapmaker
> Maps a la carte, Inc. / TopoZone.com
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> Phone: (978) 251-4242
> Fax: (978) 251-1396
> ed at topozone.com
>
>> From: Frank Warmerdam <warmerdam at POBOX.COM>
>> Reply-To: Frank Warmerdam <warmerdam at POBOX.COM>
>> Date: Thu, 14 Jun 2007 10:11:08 -0400
>> To: <MAPSERVER-USERS at LISTS.UMN.EDU>
>> Subject: Re: [UMN_MAPSERVER-USERS] Small differences in input and output
>>
>> Benoit Andrieu wrote:
>> ...
>>> Theline that is inserted in the resulting output does not seem to come 
>>> from
>>> the input neither seems to be an interpolation of the input.
>>>
>>> As a second test, I tried to offset my extent by half the resolution of 
>>> my
>>> input but in this output we can now see that a set of vertical lines is
>>> offseted.
>>>
>>> You can see my input and output :
>>> http://benoit.andrieu.free.fr/images/input.png
>>> http://benoit.andrieu.free.fr/images/output_1.png
>>> http://benoit.andrieu.free.fr/images/output_2.png
>>>
>>> As you'll see the difference is very small but I need to not have this
>>> difference.
>>
>> Benoit,
>>
>> What are you using for your EXTENT line in the mapfile?  What does
>> gdalinfo report for input.png?  The MapServer "extent" is from the
>> center of corner pixel to center of corner pixel, while the GDAL extents
>> are from the outer edge of the corner pixels.
>>
>> So if you use gdalinfo to get the extents, you need to adjust them "in"
>> by half a pixel.
>>
>> I *suspect* this is what is happening to you.  If not, please file a bug,
>> assigned to me, with a minimal map file, and input file that demonstrates
>> the problem and I'll dig into it.
>>
>> Best regards,
>> -- 
>> ---------------------------------------+--------------------------------------
>> I set the clouds in motion - turn up   | Frank Warmerdam, 
>> warmerdam at pobox.com
>> light and sound - activate the windows | http://pobox.com/~warmerdam
>> and watch the world go round - Rush    | President OSGeo, 
>> http://osgeo.org
>