[mkgmap-dev] Polyline base optimisation

Fri Apr 9 14:50:06 BST 2021

Hi Gerd

I didn't have any problem with *SameSignBak logic - compared with the
rest of it - extraBit/routeNode & house number flag array, how these
should behave for zero deltas and continuation road segments etc etc 

Ticker

On Fri, 2021-04-09 at 08:01 +0000, Gerd Petermann wrote:
> Hi Ticker,
> 
> OK, I've committed your patch as is. The (my) code in
> makeShortestBitStream() was already hard to read, maybe you find a
> better way to handle the backup/restore tricks of xSameSign and
> ySameSign?
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> Gesendet: Donnerstag, 8. April 2021 18:03
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] Polyline base optimisation
> 
> Hi Gerd
> 
> It needs to know if there are deltas < 0, deltas > 0, and number of
> bits to represent the largest delta, regardless of sign. If all the
> deltas were, say between 10..20, max=20 is significant, but min=10 is
> of no relevance; only if it was < 0 would it have an effect.
> 
> Ticker
> 
> On Thu, 2021-04-08 at 15:45 +0000, Gerd Petermann wrote:
> > Hi Ticker,
> > 
> > my understanding is that it is looking for the largest and the
> > smallest delta value. It is possible to have a smallest value > 0.
> > It probably doesn't matter because of the way how xBtits and yBits
> > is
> > calculated but I still think that your version is even more
> > confusing.
> > 
> > Gerd
> > 
> > ________________________________________
> > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > Gesendet: Donnerstag, 8. April 2021 17:34
> > An: Development list for mkgmap
> > Betreff: Re: [mkgmap-dev] Polyline base optimisation
> > 
> > Hi Gerd
> > 
> > I could have changed it to this, but it is looking for lowest val
> > <=
> > 0
> > and highest val >= 0 so 0 seemed the better choice.
> > 
> > The slight improvement is because it gives up after 2 tries that
> > don't
> > show improvement, and before, for unsigned, one of these tries was
> > wasted.
> > 
> > Ticker
> > 
> > On Thu, 2021-04-08 at 15:11 +0000, Gerd Petermann wrote:
> > > Hi Ticker,
> > > 
> > > Funny, I would have used Integer.MinValue for maxDx/maxDy to make
> > > it
> > > less confusing.
> > > Do you have an explanation for the change in size? My
> > > understanding
> > > is that your patch just skips a test which will never find a
> > > better
> > > encoding?
> > > 
> > > Gerd
> > > 
> > > ________________________________________
> > > Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im
> > > Auftrag
> > > von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> > > Gesendet: Donnerstag, 8. April 2021 13:58
> > > An: mkgmap development
> > > Betreff: [mkgmap-dev] Polyline base optimisation
> > > 
> > > Hi Gerd
> > > 
> > > If starting with unsigned deltas in polyline encoding, and
> > > attempting
> > > to reduce the length by testing reduced x/yBase values, there
> > > isn't
> > > any
> > > point in testing Base-1, as the normal number of bits will be the
> > > same
> > > (added sign bit) and there will be some overflows.
> > > 
> > > Patch attached to change this - it gives me a very slight
> > > reduction
> > > in
> > > RGN size and might give a performance improvement (I didn't
> > > detect
> > > any).
> > > 
> > > I've also fixed a couple of log. logic errors and changed minDx/y
> > > initial to 0, which is much less confusing because they are
> > > symmetric
> > > with maxDx/y which do use 0.
> > > 
> > > Ticker
> > > _______________________________________________
> > > mkgmap-dev mailing list
> > > mkgmap-dev at lists.mkgmap.org.uk
> > > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> > _______________________________________________
> > mkgmap-dev mailing list
> > mkgmap-dev at lists.mkgmap.org.uk
> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> > _______________________________________________
> > mkgmap-dev mailing list
> > mkgmap-dev at lists.mkgmap.org.uk
> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
> _______________________________________________
> mkgmap-dev mailing list
> mkgmap-dev at lists.mkgmap.org.uk
> http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev