[mkgmap-dev] Optimizing MapSplitter

Mon Nov 10 09:50:30 GMT 2014

Hi Steve,

looks promising.

If I got it right, the redraw time is influenced by 
a) how many sub divisions are overlapping a given bbox and
b) how many objects are in these sub divisions  and
c) how complex the objects are (means, how much time it takes to render them)

The optimization goal for a given bbox would be to minimize the number
of (complex) objects which are outside of the bbox, as
they have to be rendered and then ignored.
So, maybe we can calculate a ratio between "number of objects to render" and 
"number of objects in the bbox" and try to optimize (minimize) that.

As we don't have a given bbox, we may create a grid
and measure and report the ratio of each grid element.

In the past it turned out to be rather difficult to split roads
at this stage, so I'd like to leave them out and split
only shapes and normal lines.
A possible alternative to splitting roads could be to place
large road objects into their own sub division, so that
they don't contain other objects. 

I think I'll create a new branch for that stuff.

Gerd

Date: Mon, 10 Nov 2014 08:46:10 +0000
From: steve at parabola.me.uk
To: mkgmap-dev at lists.mkgmap.org.uk
Subject: Re: [mkgmap-dev] Optimizing MapSplitter

Hi Gerd

> So, what I am looking for is a tool that helps to find
> areas which are heavily overlapped, something like
> a heatmap.

When displayed it looks like this:
http://files.mkgmap.org.uk/download/223/Selection_040.png

I need to add a couple of getters and a fix to mkgmap (attached)
then I will check it all into display.

..Steve

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