[Mapserver-users] MapServer raster 'cracking' problem

[Ed McNierney]

Omry -

Take the output image you're requesting, do the math, and figure out
where the source pixels are coming from.  Examine the coordinates of the
real output pixel being generated along the "crack" and see where the
source data is coming from.  Please also look at how MapServer selects
the source data to use for a given output pixel, recognizing that
MapServer is optimized for quick image output rather than optimum image
quality, and does not combine source pixels to produce an output pixel
(in a tiled raster layer that is).

	- Ed


Ed McNierney
President and Chief Mapmaker
TopoZone.com
ed at topozone.com


-----Original Message-----
From: Omry Yadan [mailto:omry at telmap.com] 
Sent: Sunday, November 09, 2003 9:22 AM
To: Ed McNierney; Alan Steremberg
Cc: mapserver-users at lists.gis.umn.edu
Subject: RE: [Mapserver-users] MapServer raster 'cracking' problem

I reproduced the problem with only two tiles.
It was east to verify using gdalinfo that the two tiles are adjacent
along
the problematic border.
Indeed it sounds like a problem with rounding.
to reduce the amount of code to check, I can tell you that its probably
not
related to the driver of the specific format, because I reproduced it
both
with ECW and with GeoTiff (and the problem looks exactly the same, given
the
same data and map bounds).
For me, it's not urgent yet, but I would be happy to know this problem
is
history, because I currently have a solution which relies on MapServer.

	Omry.


-----Original Message-----
From: Ed McNierney [mailto:ed at topozone.com] 
Sent: Sunday, November 09, 2003 3:09 PM
To: Omry Yadan; Alan Steremberg
Cc: mapserver-users at lists.gis.umn.edu
Subject: RE: [Mapserver-users] MapServer raster 'cracking' problem

Omry -

I don't have time to look into this for a few more days, but I suspect
you are seeing an artifact of your data and rounding effects.  First,
make sure your data are as truly continuous as possible.  I think what
you're seeing is a request for a pixel that falls "between" your data
sets, or at least appears to fall between them for certain view scales.

	- Ed


Ed McNierney
President and Chief Mapmaker
TopoZone.com
ed at topozone.com


-----Original Message-----
From: Omry Yadan [mailto:omry at telmap.com] 
Sent: Sunday, November 09, 2003 3:56 AM
To: Alan Steremberg
Cc: mapserver-users at lists.gis.umn.edu
Subject: RE: [Mapserver-users] MapServer raster 'cracking' problem


This seems to be a real problem with MapServer.
Is anyone taking a look at it?

-----Original Message-----
From: Alan Steremberg [mailto:alans at wunderground.com] 
Sent: Wednesday, November 05, 2003 7:36 PM
To: Omry Yadan
Cc: mapserver-users at lists.gis.umn.edu
Subject: Re: [Mapserver-users] MapServer raster 'cracking' problem


I see the same problem using JPG or PNM files with GDAL.

Alan

----------------------------
 Alan Steremberg
 415-543-5021 x 103
 http://www.wunderground.com

On Wed, 5 Nov 2003, Omry Yadan wrote:

> I have a problem with raster image generated by map server where the
data
> source is tiled.
> The problem is that in some zoom levels (zoomed out), I get a white
line
> between two tiles sometimes.
> I ran a test with two tiles only, and I could reproduce the problem.
> the tiles boundaries are exactly one next to the other - to strengthen
the
> point :
> when I zoom into the merge line, I don't see a gap between the two
tiles.
> Initially, my data was in ECW format - to rule out ECW related issue,
I
> converted the data to GeoTiff, and I got the exact same problem (which
> appeared at the exact same requests.
>
> Any help would be appreciated.
>
> 	Omry.
>
> _______________________________________________
> Mapserver-users mailing list
> Mapserver-users at lists.gis.umn.edu
> http://lists.gis.umn.edu/mailman/listinfo/mapserver-users
>
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