[mapserver-users] Re: Corrupt image output

[Mike Leahy]

Hello again,

Just to follow-up on this, this problem isn't limited to just image 
rendering.  I also get odd results from raster queries in php mapscript 
- about half the time, I'll get appropriate rgb values, but as you can 
see in this example 
(http://img411.imageshack.us/my.php?image=corrupt2rj9.png), I don't 
always get the correct results.  Often, I'll get zeros for all three 
values, or just one value - in that sample image, the location on the 
map indicated by the red dot should have something returned for all 
three red/green/blue fields.  So perhaps this is a problem somewhere 
between mapscript and the gdal library?

Mike



Mike Leahy wrote:
> 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
> 
>