[mkgmap-dev] timed turn restrictions

Sun Mar 1 18:50:02 GMT 2009

On Mar 1, 2009, at 19:19, Mark Burton wrote:
> "Wolfgang v. Hansen" <wvhansen at fom.fgan.de> wrote:
>
>> On Sat, 28 Feb 2009, Mark Burton wrote:
>>
>>> I do not know if garmin supports restrictions that are only in force
>>> during certain hours. I have carried out web searches and found  
>>> nothing
>>> so far on that subject. If we had an example map (unlocked) that
>>> contained an example of such a restriction we would have a chance to
>>> reverse engineer it.
>>
>> Well, there is an example: The Sierichstraße in Hamburg is a one-way
>> street where the direction of traffic changes daily at 4:00 and  
>> 12:00.
>> Garmin respects this with City Navigator as I have just tested.
>
> That's very interesting. So we know it can be done. However, unless we
> can see the restriction record and learn the magic, it's going to be
> difficult to achieve.
>
>> Swiss mountain passes might help as well to understand the  
>> mechanism as
>> they are blocked in Winter and disallow routing.
>
> To me, that implies that the timing information is likely to be
> specified in additional fields being added rather than setting values
> within the existing record because there isn't a huge amount of space
> in the records that we don't understand the purpose of fully (3  
> bytes).
> That isn't enough space to be able to specify an active/inactive time
> that can be in a range of hours (probably minutes) to months.

An hour in a week can go in a byte (7*24 < 256); day in year needs 9  
bits. So it is possible (but unlikely) this goes within the three  
bytes. For those interested in experimenting, the relevant bytes are
HEADER = 0x004005
in imgfmt/app/net/RouteRestriction.java.

The other option is longer records in the restrictions table (Table  
C). Those are currently 11 bytes, but are not of fixed size.

Cheers
Robert