Status of AGG support?

Stephen Woodbridge woodbri at SWOODBRIDGE.COM
Thu Jul 5 16:56:20 EDT 2007


Here is a side by side comparison.

google-aa2 is using "PNG8"
google-agg is using "agg/png24"

     NAME "agg/png24"
     MIMETYPE "image/png; mode=24bit"
     EXTENSION "png"
     FORMATOPTION "PALETTE=/u/data/maps/palette-google-agg.txt"

ONE of the differences is mapserver-4.10 vs mapserv-4.99 and the fact 
that 4.99 has broken support for:

     NAME PNG8
     EXTENSION "png"
     MIMETYPE "image/png"

as none of the roads render.


Steve Lime wrote:
> Would be nice to have a non-tiled, side-by-side browser to do the comparison with... ;-) It doesn't
> look to me like identical mapfiles. For example, I'm looking at Chicago and there look to be some differences
> in scale settings. For example, the shape of Lake Michigan changes dramatically, see:
> I'll wait on other comments until that can be confirmed.
> Steve
>>>> On 7/4/2007 at 10:47 AM, in message <468BC11E.2050101 at>, Stephen
> Woodbridge <woodbri at SWOODBRIDGE.COM> wrote:
>> Hi Zak,
>> Thank you and the others for all the responses. I got it working this 
>> morning:
>> I have a few questions and observations:
>> The OL app above has two base layers. Both use the same mapfile, except 
>> one supports AGG and is using 5.0 and the other is using 4.10.
>> 1) Notice the white lines in the water boarding some of the polygons. 
>> What is causing that? How do you get rid of these?
>> 2) If you switch between 4.10 and 5.0 AGG base layers notice that the 
>> road widths change. What is causing this? I assume this is the same 
>> issue as the polygons above.
>> 3) If you zoom in to 15K scale of closer so street names are displayed 
>> the text looks really bad on text ALIGN FOLLOW labels. And the text is 
>> much bolder and blacker than the 4.10 example.
>> more below ...
>> Zak James wrote:
>>> Steve,
>>> In our testing, the AGG renderer is about 10% faster than GD over a
>>> variety of conditions. One caveat is that the sub-pixel positioning of
>>> vertices (which greatly improves the appearance of features) can cause
>>> far longer rendering times if suitable overview data aren't available
>>> for a given scale. We discussed but did not implement strategies for
>>> mitigating this problem. 
>> I think that discussion should get added to the RFC. If I wanted to 
>> provide my own overview data what are we talking about. Just having 
>> generalized data? Any rule of thumb on when you need to provide this?
>>> Another issue is that the antialiasing tends
>>> to cause larger image file sizes.
>> There really is not much that you can do about this. It will impact on 
>> bandwidth and tile repository sizes.
>> -Steve
>>> zak
>>> On 7/3/07, Stephen Woodbridge <woodbri at> wrote:
>>>> Paul, Steve,
>>>> A few questions:
>>>> 1) could one of you do a short post on what if anything needs to be done
>>>> to use AGG other than install the libs and select some ./configure 
>>>> options.
>>>> 2) Any sense on how this compares speed wise to the GD implementation.
>>>> 3) is what is in the trunk all that 5.0 will see or is there some
>>>> additional work that is planed to be implemented.
>>>> I would like to give it a try.
>>>> -Steve W
>>>> Paul Spencer wrote:
>>>>> The other thing that I am very keen to have is text rendered/placed
>>>>> using AGG.  Not sure if it will be done for 5.0 though.
>>>>> Cheers
>>>>> Paul
>>>>> On 3-Jul-07, at 1:25 PM, Steve Lime wrote:
>>>>>> Hi Tom: AGG support is in the codebase for 5.0. I still owe an RFC to
>>>>>> explain what was
>>>>>> done although the addition of AGG doesn't affect any other portions of
>>>>>> MapServer. It's
>>>>>> a big user feature though. I recently got a big time sink off my plate
>>>>>> and will work that up
>>>>>> ASAP.
>>>>>> The support is relatively complete. The guys from DM Solutions can
>>>>>> probably comment
>>>>>> further as they've been using it the most. The AGG vs. GD images DM
>>>>>> has supplied are
>>>>>> very nice. The quality difference is noticeable with roads in 
>>>> particular.
>>>>>> The only missing capability that I am aware of has to do with PIXMAP
>>>>>> symbols that contain
>>>>>> an alpha channel. There is a fundamental difference in how AGG and GD
>>>>>> handle alpha
>>>>>> blending (GD is flat out backwards).  We use GD to manage the pixel
>>>>>> buffer that AGG is
>>>>>> rendering into so that becomes a problem. I'll go into options in the
>>>>>> RFC.
>>>>>> Anyway, other than that the support seems to be working nicely is
>>>>>> worth trying.
>>>>>> Steve
>>>>>>>>> On 7/1/2007 at 10:08 PM, in message
>>>>>> <7b5b710d0707012008i59c41e8bq8e0ef4d8022f40f8 at>, Tom 
>>>> Beard
>>>>>> <tom at PROJECTX.CO.NZ> wrote:
>>>>>>> Hi there,
>>>>>>> This is my first time posting here, and I hope this is the right
>>>>>>> forum to
>>>>>>> ask this question.
>>>>>>> I was wondering what the status of AGG support was for the 5.0
>>>>>>> release. On
>>>>>>> searching the archives, the most recent reference I could find was 
>>>> the
>>>>>>> minutes from the May 22 IRC meeting that said that there would be 
>>>> an RFC
>>>>>>> freeze on June 15, and that an RFC for AGG was "forthcoming". Did AGG
>>>>>>> support make it into that freeze? Is it listed somewhere online?
>>>>>>> I'd also be interested to know if there is a version currently in
>>>>>>> Subversion
>>>>>>> that includes AGG sub-pixel rendering and that works well enough to
>>>>>>> have a
>>>>>>> go at compiling on Windows.
>>>>>>> Regards,
>>>>>>>             Tom Beard
>>>>> +-----------------------------------------------------------------+
>>>>> |Paul Spencer                          pspencer at    |
>>>>> +-----------------------------------------------------------------+
>>>>> |Chief Technology Officer                                         |
>>>>> |DM Solutions Group Inc       |
>>>>> +-----------------------------------------------------------------+

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