[mkgmap-dev] patch to write polygons in decreasing order

Sat Oct 29 06:39:04 BST 2016

A good guide for the extended types of blue maps is this one:
https://mega.nz/#!YV8V2ZzI!Vo9x3_tVvJhrRrErPQC8NIGKrA95AL2Up_mIDzKiadI

There is another big difference between topo maps and real blue maps:
On topo you start with an empty map that is considered all land. Then you draw water polygons such as sea or riverbank on this.
On blue you start with an empty map that is considered all water. Then you draw land polygons on this.

Until now I do not know any 3rd party maps that are real blue maps. Today all homemade maps are topos that may just look like blue maps. But this is no problem as long as you can make sure that polygons like intertidal zones, depth areas or fairways are drawn on top of the sea/riverbank polygons and not covered by them.

Von: nwillink
Gesendet: Samstag, 29. Oktober 2016 07:12
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] patch to write polygons in decreasing order

Having examined a 'blue' map more closely the polygon type structure is more
complicated:

My blue map of the Southwest coast of England  only uses extended types: ie

Here are some of the polygons:

0x10104 base map similar to 0x4a or 0x4b (Interestingly I can't detect any
4a or 4b)

0x10101 = land

0x10301 = intertidal (green)

0x10302 0x10304 -0x10305 depth areas (shades of blue)

0x10409 Danger Area

0x10507 tidal area 

etc

As stated earlier TYP files have no effect on colour nor draworder.
I looks like the imgs contain (GMP) tiles and in this respect are similar to
Garmin GB Discoverer maps etc

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