[mkgmap-dev] Re : --generate-sea for Australia?

Sat Feb 6 14:51:37 GMT 2010

Hello Thilo,

> Hello WanMil,
>
> if I understand your post correctly the problem is with the osmosis software and it's not likely to be fixed soon.

There are two problems:
1st: osmosis does not provide the boundary shape used to split the dump 
file. So mkgmap cannot differ if there is no data at a point because the 
point is outside the boundary shape of the dump or if there is no data 
because no OSM data exist there.

I'll try some ASCII graphs to explain:

b - boundary shape used by osmosis
c - coastline
- - bounding box of the dump

---bbbbbbb
|  b     b
|  bccc  b
|  b  c  b
bbbb  c  b
bc    c  b
bcccccc  b
b        b
bbbbbbbbbb

this is the input data of mkgmap:

----------
|        |
|  cccc  |
|     c  |
|c    c  |
|c    c  |
|cccccc  |
|        |
----------

And so mkgmap has a lot of options to guess what the coastline is:

----------
|        |
|  cccc  |
| c   c  |
|c    c  |
|c    c  |
|cccccc  |
|        |
----------

---c------
|  c     |
|  cccc  |
|     c  |
cc    c  |
|c    c  |
|cccccc  |
|        |
----------

----------
|        |
|cccccc  |
|c    c  |
|c    c  |
|c    c  |
|cccccc  |
|        |
----------

----------
|        |
ccccccc  |
       c  |
cc    c  |
|c    c  |
|cccccc  |
|        |
----------

...

2nd problem: The Geofabrik boundary shapes sometimes are too small. So 
the dumps do not contain all ways that mark the coastline. A prominent 
example of this is the coast of Zeebrugge in Belgium 
(http://www.openstreetmap.org/?lat=51.3406&lon=3.2152&zoom=13&layers=B000FTF). 
The Geofabrik dump does not contain lots of parts of the harbour which 
makes mkgmap guessing around what the coastline might be.

> Unfortunately this would be the software I'd use myself to extract the needed part of the planet dump. What software would you recommend to do so? I've already tried to feed the mkgmap splitter an areas.list file with only the needed areas, but that gave me a partial invalid map (MapSource wouldn't display some tiles).

You can use osmosis but you should extend your boundary shape so that 
all coastline segments are contained for sure.

>
> Regards,
> Thilo
>

WanMil