[mkgmap-dev] type/subtype of points and cities

Tue Apr 23 11:51:12 BST 2019

Hi

I think the mkgmap internal handling of types/subtypes of points is
obscure.

In the points style file, the type code is always full, ie type << 8 |
subtype, but when the points are read back from the RGN file for the
MDR processing, the representation is the same provided the subtype is
not zero, otherwise it is just type! Logic then decides that if the
value is <= 0xff it is because the subtype is zero.

It is simpler and much clearer to preserve the original representation.
This also allows unambiguous use of type 0 with subtypes, and,
possibly, city with subtypes.

It also allows the same function to be used to test a type for being in
the 'city' range, regardless of the context. mkgmap wasn't consistent
the ranges for the isCity test.

City POI are written in a different manner to the RGN file. The old
range for this was:
  type >= 0x0100 && type <= 0x1100
which I've kept, except changing to: ...& type < 0x1200. A similar
range was used for MDR5.

However, city POI are held in group 1 of MDR 9/10. This is used in Find
> City 'By Name'. The old range was: type <= 0xf, where, if the subtype
was zero, type is right shifted by 8 (see above), non-zero subtypes
messed up the testing. Now it uses the same range as above.

Actually neither of these ranges are correct for my Garmin devices.
Find > City show nearby POI with types in the range 0x0100..0x0d1f,
regardless of the img RGN or MDR. The eTrex Legend labels POIs in this
range as {Large/Medium/Small} City/Town and points in the range
0x0e00..0x111f as "*".

Find > City 'by-name' returns POI if in group 1 of MDR 9/10. I find it
a useful feature to have a POI that can be searched for but doesn't
flood the list of nearby points.

Generally, non-zero subtypes for cities cause problems in the RGN
structure and I've added a test for this to the style validation.

There is also a fix to --make-poi-index, but I can't detect any effect
of this option.

This patch won't make any difference to the img output unless the there
are points 0x1000, 0x1100.

If this patch is accepted, I'll do the equivalent to the img display
system.

Regards
Ticker
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