[mkgmap-dev] New clip box functionality for splitter

Sun Sep 16 17:08:58 BST 2012

More thoughts to greatly simplify the clipping:

As WanMil suggested all nodes would have to be stored along with a flag to 
show if it initially resides inside or outside the clip box.

Each way will then be tested in turn against the min longitude, max 
longitude, min latitude, max latitude.

Taking the min longitude test as an example:
If a way goes from inside the clip box (>= min longitude) then goes outside 
and remains outside, the way will be clipped to min longitude.
When it goes inside to outside and returns inside (>= min longitude) no clip 
occurs, and nodes between are flagged to reside inside the clip box.
If a way goes from outside clip box then goes inside and remains inside, 
the way will be clipped to min longitude.
When it goes from outside to inside and returns outside it will need to be 
determined if the way describes a line or a polygon: if a line it is 
clipped, if a polygon nodes in the way outside will be flagged to reside 
inside the clip box

Then similar is done for the other clip lines.

This would allow breathing of the clip box to to take into account highways, 
rivers etc, which go outside and return into the clip box. And get rid of 
complex polygon clipping entirely.

Any thoughts?

WanMil, I will look at the bounds utility you mentioned.

Regards, Geoff.

-----Original Message----- 
From: Geoff Sherlock
Sent: Sunday, September 16, 2012 2:42 PM
To: Development list for mkgmap
Subject: Re: [mkgmap-dev] New clip box functionality for splitter

The more I consider this the more complicated it gets. If you take the
polygon for a wood selected in JOSM and highlighted in red in the JPG
attached. Discarding everything to the left of the light blue line would
leave three closed polygons for the wood. Highways are also another worry.
If a highway goes outside the clipping area and returns into the clipping
area, should the clip bounds be auto-adjusted to allow the whole highway to
be included??? How many times should a clip bound be extended before enough
is thought to be enough??? Or should the cut be brutal, along the lines the
user entered?

Now I have used osmconvert I doubt I could write anything that would work
faster within the splitter. So I guess I will have to think of a something
else as my first project.

Regards, Geoff.

On September 16, 2012 12:19 PM, Henning wrote:

-----Original Message----- 
From: aighes
Sent: Sunday, September 16, 2012 12:19 PM
To: Development list for mkgmap
Subject: Re: [mkgmap-dev] New clip box functionality for splitter

I think using osmconvert/osmosis is the usual way and I have no problems
with it. To improve speed, you can cut a rectangular once out of a
larger extract, split it and create an areas.list-file. For secend time
(and each time after this) you use the larger extract and let splitter
cut all tiles via your created areas.list-file.

Henning

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