[mkgmap-dev] A few default stylesheet tweaks

Mon Jul 18 19:43:17 BST 2011

On Mon, Jul 18, 2011 at 01:54:43PM -0400, Greg Troxel wrote:
>>- Communication (GSM/Broadband) towers (type=communication)
>>- Powerlines (power=line)

I have been thinking of an "infrastructure" map layer that would show 
this kind of stuff. In cities, these are mostly clutter (also stuff like 
water, gas, heat and sewage pipelines), but in rural areas they can 
definitely be useful, especially when minor roads or paths are missing 
from the map.

Some time ago, I was toying with the idea of altering the style language 
so that the same style file could generate multiple output tiles in one 
pass. The style action could specify a map layer, and the mkgmap 
invocation would define the mapping of layers to output tiles (or 
specify that only the 'core layer' is to be generated).

Yes, I know that the 'multiple output tiles in one pass' is not strictly 
necessary, but I do not like the fact that the processing time is 
multiplied by the number of map layers. For 'sparse' styles, the parsing 
time seems to dominate. It is about 3 minutes per layer for 
finland.osm.pbf on my computer, and about the same time if I specify a 
'null style' that generates an empty map tile.

I would really appreciate some coding help with this. In theory, I 
should be able to achieve it in a few working days myself, but in 
practice I am getting enough (or too much) coding exercise at work, and 
this OSM hobby is supposed to be relaxing, not a chore.

>We may be getting to the point where people desire either a "topo" type 
>map or a "webmap" type map. I'm definitely in the topo camp, but 
>perhaps there should be two main styles that mostly inherit from a 
>common base. Or maybe topo is the base plus things like powerlines and 
>towers.

Multiple map layers seem to be working just fine, at least on my Edge 
705. I generate a number of 'route' layers, and can conveniently enable 
or disable the layers in the settings menu as I need them. Normally, I 
would disable all route layers, or all except one (typically 
route=bicycle or route=bus).

I have not gotten around to playing with topo layers yet, but the 
Finnish government seems to have opened the data. (ASTER and SRTM do not 
cover polar areas very well.) The Finnish topo data might not be 
available under an OSM compatible license (the terms resemble CC-BY-SA), 
but I guess I could convert it to .img tiles and let the end users 
download and combine the topo tiles with the OSM .img tiles to a 
gmapsupp.img.

Best regards,

	Marko