[mkgmap-dev] misshapen roundabouts

Thu Jul 18 09:01:18 BST 2013

of course we know about the grid.
mkgmap itself doesn't produce maps with higher accuracy - and rounds of 
course.  So the more points a roundabout has, the uglier it becomes.

The real problem is not there yet! However it starts appearing with 
micromapping sidewalks. Yuck - in some districts in Vienna, people have 
nearly mapped all sidewalks. Those are of course connected to the 
street, and mean no more straight crossings exist - as due to rounding 
crossings now often need to be moved around in order to connect to the 
sidewalks properly.

I deem in future we need to have an option in the style-file - to 
declare ways, which should be moved by mkgmap in such a way, that the 
resulting connection lies on a straight line of the other ways it meets! 
Else as soon as this micromapping gets more - the will be no more usable 
maps in cities. (not showing these ways is no help, as there are now 
additional nodes as part of the streets, and there needs to be some 
clever algorythm to delete such nodes.

(yuck, besides mapping every waste-bin, people here now start to map 
every gully, ways, rooms and doors inside buildings for every floor, and 
so on -- only advantage is that housenumbers are more or less complete 
now around such areas. That is besides soon approaching the finish of 
having mapped every single tree that exists outside of forests in 
Vienna. OSM is soon to have more data here than a cadastre map, so no 
more a streetmap but a cadastre).
On 18.07.2013 09:25, Kay F. Jahnke wrote:
> I think I finally found what the problem is: the garmin devices can't
> handle the precise data I want them to display, look at these two quotes:
>
> 1. from http://www.cgpsmapper.com/download/GM8DocV2.pdf
>
> When declaring the location of objects in the world, the highest
> precision available uses 24 bits of resolution, which resolves to an
> accuracy of about 2.5 meters.
>
> 2. in 'Garmin IMG File Format' by John Mechalas:
>
> The reference coordinates in the TRE section are given as 24-bit
> integers (three bytes). This implies that the maximum granularity for
> map elements in the image file is approximately .0000214576721 degrees
> of latitude or longitude. At the equator, a degree of latitude is
> roughly 365228.16 feet, making the highest resolution for map points
> about 7.8369461 feet.
>
> So even if we have precise coordinates in OSM, in the garmin image they
> will be rounded to the nearest(?) grid point. In fact, everything on the
> garmin map looks like it's been snapped-to-grid, if you look at it closely.
>
> Sorry for the noise; maybe my posting is still helpful for others facing
> the same problem.
>
> Kay
>
>
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://lists.mkgmap.org.uk/mailman/listinfo/mkgmap-dev

-- 
keep on biking and discovering new trails

Felix
openmtbmap.org & www.velomap.org