[mkgmap-dev] polygon splitting/more than 255 polygons errors

Sun Sep 4 21:01:51 BST 2011

> Hi,
>
> On Fri, Sep 2, 2011 at 9:26 PM, Richard<rz at linux-m68k.org>  wrote:
>> Hi,
>>
>>>> I have recently downloaded some mkgmap generated maps that produce this error when displayed
>>>> in navit:
>>>> :garmin_obj.c:1279:1|:Error more than 255 polygons/lines in a subdiv are not supported
>>>
>>> This does not look like an mkgmap problem to me. Reading the error
>>> message I assume that navit does not support subdivisions containing
>>> more than 255 polygons + lines. But as far as I know there is no such a
>>> limit for garmin devices.
>>
>> looks like the message comes from libgarmin. If you think its an error in libgarmin
>> I will have a look at that.
>
> The message is indeed from libgarmin, but if someone proves that
> polygons can be more than 255
> fixing wouldn't be so trivial.
>
> 255 limit comes from garmin object addressing - in mdr(index file) you have
> subdiv(2 bytes):object(1 byte). there are references to this in the
> various sections
> in img file itself, lbl sections.
>
> If someone have noticed for example that polylines and polygons can be
> indexed too mdr sections before first poi section describing variuous
> types available for search seen in an  old metroguide map that can
> fake Lake Someranodmbiglake name.
>

I tried to check with a simple testcase if more than 255 polygons in one 
subdivision are supported. But it's not so easy as I expected. I created 
a single OSM file with 256 lakes (natural=water) close together. But 
MapSource cuts the lakes on virtual borders around the map and doesn't 
display them in each zoom level. MapSource is not bugfree but when I see 
the result of such a simple file I assume there's more wrong with the 
subdivision handling of mkgmap.

Also using less than 256 polygons (e.g. 64) does not give better results.

So I cannot give a clear answer till now.

WanMil