[mkgmap-dev] Numerical comparison of two tags

Fri Nov 1 12:50:01 GMT 2013

I'd like to set maxspeed to the minimum of maxspeed, maxspeed:forward, 
and maxspeed:backward.
In my lines file, I use:

|maxspeed:forward=*&  maxspeed!=* { set maxspeed='${maxspeed:forward}' }
maxspeed:forward=*&  (maxspeed:forward<maxspeed) { set maxspeed='${maxspeed:forward}' }
maxspeed:backward=*&  maxspeed!=* { set maxspeed='${maxspeed:backward}' }
maxspeed:backward=*&  (maxspeed:backward<maxspeed) { set maxspeed='${maxspeed:backward}' }|

That works only if exactly one tag is set. But when both forward and 
backward are available, I get the value of forward even if backward is 
less. An example is wayhttp://www.openstreetmap.org/browse/way/70594951.

I played with additional / different rules, and my conclusion is that it 
is NOT POSSIBLE to compare the values of two tags with each other.

For example, I tried:

|highway=*&  maxspeed!=* { set maxspeed=999 }
maxspeed:forward=*&  (maxspeed:forward<maxspeed) { set maxspeed='${maxspeed:forward}' }
maxspeed:backward=*&  (maxspeed:backward<maxspeed) { set maxspeed='${maxspeed:backward}' }|

And you can guess the result: maxspeed=999, for that way with 
maxspeed:forward=60 and maxspeed:backward=40.

Is my conclusion correct?
And, if so, will there be a patch?
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