[mapserver-users] Corrupt image output

[Mike Leahy]

Ok, I'll file a ticket shortly...but I have a few more things I've tried 
that might add insight to this.  It seems if I load the map via cgi 
mapserver, I get the same problems - so this isn't limited to mapscript. 
  In contrast, I don't seem to have any trouble with the output values 
if I extract a single pixel from an image using gdal_translate to a 
*.grd file (at the same coordinates where I get corrupt results from 
mapscript/mapserver) - so the problem doesn't seem to be with gdal by 
itself.

Also, I can point out that the corrupted areas in the output have no 
coincidence with tile-index boundaries.  I say this out because if I 
render a layer from a non-tiled image dataset, the corrupted areas 
appear as horizontal bands across the entire width of the image output, 
rather than rectangular areas (though my non-tiled dataset is a 
single-band floating-point DEM, rather than an rgb image).  However, as 
before, the height and number of lines of each band is variable.

Maybe it's just time to upgrade my OS (F7 is EOL after all).

Regards,
Mike

Tamas Szekeres wrote:
> Mike,
> 
> It's quite difficult to find out what's going on. You should file a
> ticket including the example and sample data. Probably the problem may
> be reproduced in other machines as well.
> 
> Best regards,
> 
> Tamas
> 
> 
> 
> 2008/8/19 Mike Leahy <mgleahy at alumni.uwaterloo.ca>:
>> Tamas,
>>
>> I just gave this a try a few times - deleted the cache, and loaded one tile.
>>  It seems to happen less frequently, but I still have about a 1 in 3 chance
>> of getting various rectangle artifacts on the image.  It basically looks
>> like something forgets to draw one or more of the rgb colours.
>>
>> Mike
>>
>> Tamas Szekeres wrote:
>>> Mike,
>>>
>>> Did you experience the same problem when calling tile.php directly
>>> when rendering an individual tile?
>>>
>>> Best regards,
>>>
>>> Tamas
>>>
>>>
>>> 2008/8/19 Mike Leahy <mgleahy at alumni.uwaterloo.ca>:
>>>> Hello list,
>>>>
>>>> I'm wondering if anyone can help me figure out a problem I'm having with
>>>> corrupted output from from a tiled geotiff dataset I'm using in a ka-Map
>>>> environment.  You can see what's happening to the imagery here:
>>>> http://img527.imageshack.us/my.php?image=corrupthd1.png
>>>>
>>>> This generally happens when I'm zoomed in fairly close, and usually with
>>>> this high-resolution image dataset.  However, I can get corrupted output
>>>> for
>>>> other raster datasets (all geotiff, but not always tiled).  It seems to
>>>> happen when the machine is processing most intensively (i.e., usually
>>>> when
>>>> the imagery is being rendered by ka-Map).  It also seems to be limited to
>>>> the laptop I am using, which is running F7-x86_64.  In contrast, I have
>>>> an
>>>> actual server (F8-x86_64), which has a virtually identical setup (with
>>>> respect to MapServer and its various dependencies), but with lots more
>>>> cpu
>>>> cores and ram, and it's having no trouble at all (as far as I have
>>>> noticed).
>>>>
>>>> The corruption in the output from the same application my laptop is not
>>>> always the same - if I clear the cache for ka-Map and re-render the
>>>> images,
>>>> I'll get similar artifacts appearing in the output (red, green, blue
>>>> and/or
>>>> black rectangles), but they will vary in size and location.  It happens
>>>> for
>>>> both GD/AGG drivers, and JPEG/PNG output formats.
>>>>
>>>> Until now, I figured it was just a problem with limited memory on my
>>>> laptop
>>>> (it was always around 100% when rendering this imagery on the web service
>>>> +
>>>> viewing the application in a browser), but now I've upgraded the ram -
>>>> there's plenty of spare room and I'm still getting the same problem.  I
>>>> just
>>>> finished upgrading Gdal from 1.5.0 to 1.5.2, and that didn't help any.
>>>>
>>>> Basically, the only real differences I can think of between my laptop and
>>>> my
>>>> server are the number of cpu cores (1 on my laptop vs. 8 on the server),
>>>> and
>>>> possibly the versions of some of the underlying libraries in the system.
>>>>  Does anyone know where I should start looking to find the cause of this?
>>>>  Or perhaps somebody recognizes this problem, and knows what I might be
>>>> doing wrong...
>>>>
>>>> Thanks for any suggestions,
>>>> Mike
>>>>
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>>>>
>