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[mkgmap-dev] Did anyone realize cGPSmapper speaks Garmin NT?

From Felix Hartmann extremecarver at gmail.com on Tue Apr 26 18:21:55 BST 2011

On 26.04.2011 19:08, WanMil wrote:
>>> Hi list
>>> I remember many discussions and comments about how mkgmap produces
>>> Garmin's legacy format only and the NT format is still a mystery. 
>>> Today,
>>> I was pointed at a discussion of the Polish UMP project (similar to 
>>> OSM,
>>> strongly concentrated on Poland and surrounds). As I happen to be 
>>> Polish
>>> and thus read the language, I browsed their wiki. I noticed that they
>>> are producing Garmin NT maps. And then I found that their tool chain is
>>> based on cGPSmapper [1]. So, is the Garmin NT format considered reverse
>>> engineered now that the cGPSmapper source is open? Or has this
>> cgpsmapper is not open source. Only parts of it are open sourced.
>> Well lets hope all of it becomes open source (for one example address
>> index by cgsmapper seems to be more correct than mkgmap address index).
>> NT format should be optional in any case. Old GPS like all etrex series
>> or 60CSx work much slower once an NT map is loaded (even if it is
>> deactivated).
>>> interesting fact been missed somehow (I certainly was unaware of it
>>> until today)?
>>> - Bartosz
> What's the difference between 'old' Garmin format and NT format?
> Is it that NT maps are using the GMP subformat to group tiles into 
> larger packages? Or are there any other specifics?
NT is a compression. It takes less space for maps that have autorouting 
data, it takes more space for all non autorouting objects AFAIK. Also it 
needs more processor power on GPS.
It has nothing to do with GMP subformat.
Basically no additional features require NT. (not even 3d buildings or 
"lanes" or "real junction view" and so on). I think 1 or 2 special 
things need NT format though.
> Support for the GMP subformat should be possible. Some time ago I have 
> written a parser of the GMP subformat for the display project and that 
> was not a very big deal.
> WanMil

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