interaction of linejoin/linecap/approximation_scale on rendering perf in mapnik when drawing lines

gistfile1.txt

# line symbolizer on 10m-admin-0-countries.shp
* linejoin can double line rendering times
* approximation scale can mostly avoid, but ideally don't use linejoin unless absolutely necessary

## default line symbolizer
  $ howfast.py world_merc.xml 10
  min: 0.2484 | avg: 0.2500 | total: 2.4999

## additional impact of "round" linejoin
  min: 0.3711 | avg: 0.3736 | total: 3.7358

## additional impact of "round" linecap
  min: 0.2524 | avg: 0.2536 | total: 2.5358

## "round" linejoin + approximation-scale=.1
  min: 0.3233 | avg: 0.3249 | total: 3.2493

## "round" linejoin + approximation-scale=.01
  min: 0.2608 | avg: 0.2622 | total: 2.6220