[mkgmap-dev] splitter maximum tile size

Wed Dec 5 11:33:24 GMT 2012

Am 05.12.2012 12:18, schrieb GerdP:
> Henning Scholland wrote
>> So there are several cases:
>>
>> 1: several distinct areas in oneinput-file (eg Iceland and Germany or
>> France and all there islands)
>> -> splitter should stop and ask the user to use al polygon-file or
>> create a polygon-file itself and warn user, that h did so
>>
>> 2: Map crossing 180/-180
>> -> split bounding-box at 180/-180 and calculate tiles for each of the
>> two bounding-boxes
>>
>> 2a: Map crossing 180/-180, but covers hole planet as input
>> -> use bounding-box left=-180 right=180
> Yes, there are many cases, but it is not always easy for splitter to find
> out what
> the user did to create the input file. Splitter doesn't "know" that Europe
> exists and
> how many nodes it should find in that area.
> This could be changed if we always feed splitter with a file containing the
> densityMap
> for planet, but that wouldn't make it much easier to find out what tiles the
> user wants.
>
> Reg. "create a polygon-file" :
> A possible algorithm for that could try to find bounding boxes that are not
> too big and have nice aspect ratio. It would prefer areas with few nodes to
> areas that are very big.
>
> I am not sure if this is good enough, but I think it's worth trying.
> OK?

Hmm...for splitter my case 1 and 2 seems to be the same. He don't know 
what world continues on the other side of 180/-180.

I think the density-map of splitter is like a table and each field 
contains the node-density for n° x n°. Then splitter adds them to eg. 1° 
x 1°-Tiles. If there is a density of zero, remove this tile. I don't 
know if 1° x 1° is a good value, it's just an example. It should be big 
enough, that also deserts have a density > 0.

Splitter can now create a simple bounding polygon. This wont be perfect, 
but it's a starting-point. Also splitter should ask the user to improve 
the poly-file for better results.

Henning