[mkgmap-dev] Re: my map testing

Thu Dec 11 21:45:16 GMT 2008

On Dec 11, 2008, at 18:05, Alexander Atanasov wrote:
> Ignore the prev diff.
> Actually the extrabit is before deltas, not after them.

A bitstream appears to be as follows:

signinfo
extra bit 0
deltas 1
extra bit 1
deltas 2
extra bit 2
...
deltas n
extra bit n

I.e., there's n+1 extra bits for n deltas. This is a little hard to  
track down because the last extra bit is usually zero, but there are  
cases where it isn't. But even if it's zero, this bit may mean that an  
extra zero byte is written. That last extra bit went in with r730,  
fixing some problems.

Now, suppose "deltas k" describe "coordinate k" (with the polyline  
starting at coordinate 0). It's kind of open whether "extra bit k"  
should be associated with coordinate k, with coordinate k+1, or with  
the line segment between coordinates k and k+1.

But associating extra bit k with coordinate k offers the easiest  
interpretation of the extra bits I've seen: Except for extra bit 0 and  
extra bit n, extra bit k is set iff coordinate k is a node. I've never  
seen extra bit 0 set, and I believe extra bit n is set iff coordinate  
n is a node of the road, but not the last node.

All quite unsure, though.

Cheers
Robert