[mkgmap-dev] bugreport for new splitter

Mon Aug 10 21:32:40 BST 2009

Greg Troxel wrote:
> Dermot McNally <dermotm at gmail.com> writes:
>
>   
>> 2009/8/10 Greg Troxel <gdt at ir.bbn.com>:
>>
>>     
>>> For receivers with a 2GB uSD, I think one wants tiles pretty big.  I
>>> have 2009 vintage Garmin proprietary maps, and all of New England is in
>>> 2 tiles, and the .img I think are about 25 MB each.  I also have a 2002
>>> or 2003 vintage receiver and proprietary map data, and that has tiles
>>> that are about 1-4MB.  This lets me choose what I want to fit in the 19
>>> MB internal memory.  There are still some devices like that around and
>>> useful, so I can see a demand for ~3 MB tiles.  But, for the 2GB types,
>>> tiles that are more like 25 MB seem better.
>>>       
>> Greg, is that map with the larger tiles in NT format? I've noticed
>> that these tend to be bigger, and indeed, the devices that support
>> this format are also newer and more powerful.
>>     
>
> Yes, the 2003 is the old format (I think), and the larger tiles
> definitely NT.  But, you can get an etrex without the uSD (why you
> would, I don't know, but you can) and those have I think 24MB of
> internal memory, which is not all that different from 19MB.  I think the
> NT tiles will fit one of them in that, which is great unless you are on
> the border between two tiles.
>
> I don't know if NT is more or less space efficient.  I can't imagine
> it's all that different.
>
>   
NT saves about 30% (look at City Navigator Classic vs City Navigator 
size). However it needs much more processing power on GPS to display. On 
etrex or 60CSx units you should allways use non NT maps. There are many 
pseudo NT maps around by Garmin however. (you can get the same effect 
with gmaptool "create pseudo NT map".).
I don't know any advantage other than size of NT so I don't think it 
should be a high priority to decipher NT maps to teach mkgmap to write 
NT .img maps. Currently depending on the number of POI you can create 
maps up to around 30MB with mkgmap.

Also most 3rd party .img viewers can't show NT maps.

By now nearly all Garmin Units if using newest firmware can have 4GB big 
gmapsupp.img. With Oregon/Colorado/Nuvi and all other Garmin GPS 
building on the NUVI platform, the gps does not need the maps to be 
called gmapsupp.img but gmapsup1.img or even random names will work too. 
I becomes pointless therefore to be able to write mapsets bigger 2GB 
(City Navigator Classic Europe and newest CN are over 2GB, I don't know 
any other single map to be so large).

One great thing for having a huge tile would be to use it to flash the 
basemap with OSM basemap. But then internal memory for basemap on old 
units is pretty small, and on NUVI platform gps basemap does not offer 
much advantage....
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