[mkgmap-dev] [Patch v1] avoid wrong bearing results

Thu Oct 31 19:36:54 GMT 2013

On Thu, Oct 31, 2013 at 10:08:53AM -0700, GerdP wrote:
>a few weeks ago I suggested that we might need higher precision in the
>Coord class.
>
>Attached patch is a quick hack to implement this.
>If I got it right, this may allow to remove a lot
>of code that tries to correct what the rounding had
>done wrong. For the beginning, I've used the
>precise values only for bearing calculations,
>as I think that this is most important.
>
>high_precision_coord_v1.patch
><http://gis.19327.n5.nabble.com/file/n5783533/high_precision_coord_v1.patch>
>
>Please let me know what you think about it.

This sounds interesting. I tried it out on finland.osm.pbf, wondering if 
it would make some of the bogus warnings for anti-islands go away.  
(There are some very tiny islets or rocks mapped as natural=coastline.)

I guess, it is to be expected that your patch does not yet fix bogus 
warnings about the direction of hyper-precisely mapped roundabouts or 
tiny coastline polygons. Here is an example that I got with your patch:

2013/10/31 21:16:32 WARNING (SeaGenerator): 63240002.osm.pbf: Converting 
anti-island starting at 
http://www.openstreetmap.org/?mlat=60.21780&mlon=25.30937&zoom=17 into 
an island as it is surrounded by water

This is http://www.openstreetmap.org/browse/way/241289746, a tiny islet, 
properly mapped in counterclockwise direction.

For some reason, current svn head (r2795) with your patch is producing 
more error messages than the revision I used earlier (I guess r2640).  
With the old mkgmap, I got 545041 bytes of log, and with the patched 
r2795, I got 774890 bytes, for the same input. The map sizes grew too:

  Length   Method    Size  Cmpr    Date    Time   CRC-32   Name
142065664  Defl:X 113283124  20% 2013-10-31 05:23 05eede3d  gmapsupp.img
143736832  Defl:X 114490132  20% 2013-10-31 05:23 662f2ea9  gmapsupp.img

(The timestamp is that of the finland.osm.pbf file.)

Best regards,

	Marko