[Maposmatic-dev] Scale issue in booklet layout

[David MENTRE]

Hello,

2012/4/10 Thomas Petazzoni <address@hidden>:
>  * Gaël patches on the scale problem has also changed significantly the
>   scale of booklets. The city of Chavagne required sixteen A4 portrait
>   pages before Gaël patches (just for the divided map) and now
>   requires 28 pages (just for the divided map) after Gaël patches. I
>   think the previous version with 16 pages was readable, so I guess we
>   should change the scale used for booklets to something more
>   reasonable.

I started to look at it.

The requested Mapnik scale should be 1/12000 so we are at zoom level
16 (OSM zoom level 16 is between 1/5000 and 1/12500, see
stylesheet/maposmatic-printable/inc/entities.xml.inc).

* When rendering a poster layout of Chavagne (no specified paper size):
  * The Mapnik scale used is 1/11848 (quite close to our requested 1/12000)

  * Actual map scale is 1/6331

* When rendering a multi-page layout of Chavagne (on A4 paper size):
  * The Mapnik scale used is 1/8089 (this is the bug)

  * The actual map scale is between 1/4323 and 1/4326.

I currently don't understand why we have this 1/8089 Mapnik scale. The
scale computation seems pretty similar to single_page_renderer.
Multiplying the multi_page_renderer default scale by 1.5 (the
approximate error ratio between 1/12000 and 1/18089) "fixes" the issue
(i.e. we would have 16 pages for Chavagne).

Best regards,
d.