[mkgmap-dev] natural=wetland; why is ~ disallowed at top level?

Mon Jan 18 07:47:31 GMT 2010

Hi Steve,

> If there are multiple rules with the first term natural=mud then they
> are put into a list in the order that they occur in the file. They are
> then evaluated in order until one matches.  Only the conditions after
> natural=mud are run, eg for the rules:
> 
>    natural=mud & colour=brown [0x50 ...]
>    natural=mud [0x51 ...]
> 
> you create a list of instructions that does the following:
>    if colour == brown then return [0x50, ...]
>    return [0x51, ...]

I see.  I guess that only the first matching [] rule will be run
and that any {set} or {add} rules will not affect further tests.

> > 3. Why doesn't RuleFileReader.optimiseAndSaveBinaryOp() check for
> > second.isType(EXISTS)?  Why doesn't it attempt to swap operands when
> > first.isType(NOT_EXISTS)?
> No particular reason other than I am never tempted to start a rule
> with !=.
> 
> So yes you could rewrite (eg):
>    a!=b & c=*
> as
>    c=* & a!=b
> that would be valid.

OK, I will fix that in the parser, because it makes the language cleaner
in my eyes (regular, symmetric, orthogonal, for want of a better word).
The same would apply to second.isType(OR), I suppose.

One last question.  The attached patch does not affect runtime much
(similar amount of difference in execution time can be observed between
repeated runs), but it affects the map generation:

-rw-r--r-- 1 marko marko 45474816 18.1. 09:00 gmapsupp.img
-rw-r--r-- 1 marko marko 45475840 16.1. 22:17 gmapsupp-nop.img
-rw-r--r-- 1 marko marko 45475840 18.1. 09:13 gmapsupp.img

The first gmapsupp.img was generated with the patch applied, the latter two
without.  As far as I understood your explanation, these would be executed
the same, under the highway=* key.  (This would not change even if I added
the above-mentioned tweakings for second.isType(), because
the first.isType(EXISTS) would be checked before second.isType() in any case.)

Do you have any idea why the surface ~ '...\|...' would omit some definitions
that are included by the surface=... | surface=...?

Best regards,

	Marko
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