[OSM-dev] bad pngs from mod_tile / renderd & meta files

jburns jzburns at gmail.com
Sat May 2 11:30:05 BST 2009




Iván Sánchez Ortega-3 wrote:
> 
> 
> Hi,
> after running
> 
> wget localhost/tiles/0/0/0.png
> 
> then the command:
> 
> /opt/csw/bin/hexdump 0.png |more
> 
> I see this output:
> 
> 0000  4d 45 54 41 40 00 00 00  00 00 00 00 00 00 00 00  META at ... ........
> 0010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0070  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0080  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0090  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 00a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 00b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 00c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 00d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 00e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 00f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0100  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0110  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0120  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0130  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0140  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0150  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0160  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 0170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  ........ ........
> 
> sometime later in the file I see:
> 
> 2150  00 00 00 00 89 50 4e 47  0d 0a 1a 0a 00 00 00 0d  .....PNG ........
> 2160  49 48 44 52 00 00 01 00  00 00 01 00 08 03 00 00  IHDR.... ........
> 2170  00 6b ac 58 54 00 00 00  90 50 4c 54 45 b5 d0 d0  .k.XT... .PLTE...
> 2180  b9 d1 d0 bc d2 d1 be d4  d2 be d4 d4 c0 d3 d2 c0  ........ ........
> 2190  d4 d2 c1 d5 d4 c4 d3 d2  c4 d5 d2 c4 d6 d5 c6 d8  ........ ........
> 21a0  d6 c8 d6 d4 c9 d9 d6 cc  d9 d6 cd dc d7 ca d9 d8  ........ ........
> 
> which I think is the start of a PNG? Not sure. My feeling is that the meta
> file creation is faulty somewhere. Any further clues in debugging renderd?
> 
> Many thanks
> 
> John
> 
> 
> El Viernes, 1 de Mayo de 2009, jburns escribió:
>> I am having a problem in that the pngs being generated and returned by my
>> apache & renderd & mapnik process are not "proper" pngs in that they are
>> rejected by various file viewers as being malformed.
> [...]
>> Any ideas or tips where to start debugging this one?
> 
> First thing I'd do is to really check that the pngs are malformed. Please
> try 
> this:
> 
> $ wget localhost/tiles/0/0/0.png
> $ hexdump -c 0.png | head
> 
> You should see something like this:
> 
> 0000000 211   P   N   G  \r  \n 032  \n  \0  \0  \0  \r   I   H   D   R
> 0000010  \0  \0 001  \0  \0  \0 001  \0  \b 003  \0  \0  \0   k 254   X
> 
> 
> What exactly do you see when you do an hexdump of one of our PNGs??
> Sometimes, 
> when there is an error while generating the image, you may see an error 
> message intertwined in there.
> 
> 
> Cheers,
> -- 
> ----------------------------------
> Iván Sánchez Ortega <ivan at sanchezortega.es>
> 
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> 
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