[mkgmap-dev] Crash in NodCheck

Wed Jul 8 17:34:09 BST 2020

Hi Gerd

 > the current code in NodCheck (NodFile.java) stops reading route nodes 
when
 > 	    if (low == 0 && flags == 0)
 > 		    return null;

Yes your right that check is not needed, because we know the correct
size of the section.  I've found a few cases where it is wrong
since  there is only a single spare zero byte at the end of
the center.

 > The code in mkgmap may write route nodes where both values are 0. If 
I got that right this happens when the node is (one of) the last nodes 
in a route center.

On the other hand I couldn't find any cases in my maps of flags being
0x00.  In fact none with the top nibble as 0.

 > With current mkgmap the nodes in one route center are sorted by 
position. NodCheck doesn't seem to verify this so I assume there is no 
need for this order.
 > Maybe the nodes in Garmin maps have a different order? For example, 
nodes with flags == 0 could come first?

Garmin maps appear to sorted by position - at least by longitude,
although maybe not latitude as mkgmap does.  It is possible that there
is some secondary sort condition that we have not found yet.

 From what I've just found there seems to be some kind of sorting
on destclass.  The first center tends to be all destclass=0 and the
last one destclass=4.

Steve