[mkgmap-dev] Optimizing MapSplitter

Thu Nov 13 11:11:45 GMT 2014

On 12/11/14 22:19, Andrzej Popowski wrote:
> I have prepared a tile in a way you have suggested. See files here:
> http://files.mkgmap.org.uk/download/224/test.7z
>
> Archive include following maps:
> 29483019.img - map compiled by mkgmap with mkgm-test.bat
> 29483018.img - map recompiled by cGPSmapper with TreSize=511
> 29483017.img - map recompiled by cGPSmapper with default TreSize

As part of the div display program I keep track of the sizes of the
subdivisions and count them in buckets of their log10() value.

29483017.img cgpsmapper default tre size
------------
Total elements: 142725
Number of divs: 423
Average elements per div 337
  0: 0
  1: 0
  2: 0
  3: 0
  4: 1
  5: 50
  6: 121
  7: 250
  8: 0
  9: 1

This means that there is 1 division that is between 10,000 and 99,999
units square, 50 that are between 100,000 and 999,999 units square
etc.

So there is a high number of elements per division and most divisions are
greater than 1,000,000 units square. Indeed more than half are greater
than 10,000,000 units square.

29483018.img cgpsmapper tre size 511
-------------
Total elements: 161337
Number of divs: 3979
Average elements per div 40
  0: 0
  1: 1
  2: 7
  3: 12
  4: 177
  5: 3625
  6: 154
  7: 0
  8: 0
  9: 1

There are a lot more divisions and most of them are less than
1,000,000 units square.

29483019.img mkgmap
------------
Total elements: 142579
Number of divs: 367
Average elements per div 388
  0: 0
  1: 0
  2: 0
  3: 0
  4: 0
  5: 63
  6: 215
  7: 76
  8: 13
  9: 0

The mkgmap map has a low number of subdivisions and more than half
are less than 10,000,000 units square.
It therefore falls somewhat between the two cgpsmapper maps.

It would be interesting if an even smaller tresize produced a faster
map.

..Steve