[OSGeo-Discuss] How to assess rendering quality?

[Jody Garnett]

Gilles Bassière wrote:
> Hi list,
>
> I'm doing a comparative study of OpenSource cartographic servers 
> (Mapserver, Geoserver and Mapnik). Beside raw performance and 
> features, I'd like to assess the rendering quality, say how pretty 
> produced maps are. Precisely, I'm interested in the quality of the 
> drawing work, my point is not about symbology, nor styling of maps.
>
> I have some problems to find a set of objective criteria I could 
> benchmark my servers against. So far, I have already identified the 
> following:
> - sharpness of details
> - smoothness of lines
I like how sharpness of details and smoothness of lines are in conflict :-)
> - uniformity of colors
>
> I'm open to any comments. Do you think these criteria are consistent 
> regarding the purpose of my study? Does anyone have other criteria to 
> suggest?
All my advice falls under symbology / styling and how well a map 
communicates.

It is going to be very difficult to access quality in an objective 
manner; here are a couple of ideas:
- Compare the full colour PNG formats to close the applications can come 
to that using 8=bit PNG or JPeg
- Compare ability to labeling (if you do not consider that styling)

If you can load your own data into the different environments a range of 
different tests should open up for you:
- compare image at different scales; notice when features "cut out"
- see how well they do at rendering narrow polygons; subtract points if 
the resulting map looks invalid
- zoom out and notice how well features (and labels) converge or are 
combined

Best of luck for what should be a really interesting write up; I am 
looking forward to seeing how MapServer 4 does against MapServer 5.


Jody