[mkgmap-dev] Option "preserve-element-order"

Wed Jul 1 11:25:51 BST 2009

First to understand, mapsource like gps drawn things on top of each 
other, thus what gets drawn first ends up on below things drawn later. 
On GPS this is even more noticable than in Mapsource.

Drawing order on GPS:
1. Polygons (doesn't matter which layer nor map-id,) --> polygons 
themselves by draw order in typfile.
2. Polylines (layers get drawn first lowest map-id to highest map.id, 
thus lower higher layers are drawn on top of  lower highway map-id 
layers) - this behaviour is opposite to what Mapsource does. Polylines 
themselves if not organised by map-id layers get drawn according to 1. 
type (some types behave differently), 2. id.
3. POI (depends on ID and type) - allways on top of polygons and polylines

Drawing order in Mapsource <= 6.13.7. (I don't use crapsource >=6.14.1 
which works differently again and is blody slow, and overcomes this by 
caching the map so you don't notice how crappy it's performance really 
is, but loads up to 20GB of temp files onto my 1.5TB harddisk, also 
antialising depending on graphic card gets tedious for the eyes - as 
everything gets cached before showing up difficult to analyse what gets 
drawn first.)
1. Overall order is defined by map-id layers. layers get preference, so 
polygons have to be in lowest layer (map-id). Polygons themselves are 
organised by draw order primarily and either type or id (have not 
figured this out yet)
2. Streets, layers opposite to GPS, types the same way as on GPS. thus 
0x01 is drawn usually lowest.
3. POI Have not figured it out, seems to depend on type and map-id.

Thilo Hannemann wrote:
> Thank you for all the quick feedback.
>
> What I am after is the drawing order of lines.
>
> I use the overlay feature of mkgmap with the "overlays" style file. 
> Using this feature one way in the OSM data will create several ways 
> with an identical location in the IMG file, but with different Garmin 
> IDs. Those ways get always added in the same order to the IMG file. So 
> I should be able to use this feature to create more complex line 
> styles by overlaying Garmin IDs. Another thing I use is a patch that 
> allows me to generate ways from relations (I've published it some time 
> ago on this mailing list). The relations are handled before the 
> points, lines and shapes are handled, so they are always first in the 
> IMG files.
>
> The thing is: It doesn't work. What is even worse is that I get 
> different drawing order whether I view the map on the computer or on a 
> GPS unit. Attached are some screenshots of the same area using the 
> same IMG files. The thing to look at are the cycle route in blue 
> (generated from relations) and the cycleways that go alongside roads 
> (the blue dotted lines on both sides of a way, generated as an overlay).
>
>
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> MapSource and RoadTrip draw the cycle way at the bottom of the screen 
> (along Hofmannstrasse) behind the road, but the nüvi 255W and the 
> Oregon 300 draw it on top of the road. The same is the situation with 
> the cycle way at the upper left corner (along Gebbertstrasse). On the 
> computer it is drawn behind the road while the GPS units draw it on 
> top of the road.
>
> It would be nice if that behaviour would be at least consistent. But 
> it isn't. I also get roads drawn on top of the cycle routes on the GPS 
> units.
>
> Has anybody any idea what is happening here?
>
> Regards
> Thilo
>
> ------------------------------------------------------------------------
>
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> mkgmap-dev at lists.mkgmap.org.uk
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