[mkgmap-dev] [Patch v1] Oneway handling

Tue May 14 21:09:44 BST 2013

Hi Gerd,

I don't know if your patch makes sense or not.
But let's start thinking loud (the following thoughts might be 
completely wrong!!!):

The LineMergeFilter should not modify routing at all. This is (should 
be?) catched by the rule that lines are merged only if resolution < 24 
or the line is no road. That also means that merging is only a cosmetic 
and performance change.
Cosmetic: the lines are getting longer and therefore they will be 
visible to resolutions with lower number because the subsequent filter 
work better with longer lines.
Performance: fewer objects and smaller img size for the device to display.

Merging of lines changes the behaviour of subsequent filters. You've 
found a good example with Minkos way and the DouglasPeuckerFilter. When 
having a look at this example I think the LineMergeFilter should not 
merge lines to closed ways (unless they are roundabouts). If a way is 
already closed it should not be merged any more.

Despite the absence of detailed knowledge of the map format I think that 
the oneway flag should not matter in resolutions < 24. Overlays with 
oneway arrows depend on the fact that they use a typ file with specific 
images. Having two ways A (oneway=yes) and B (oneway=no) you will have 
three MapLine objects:
Object 1 type 0x06 derived from A
Object 2 type 0x1022 derived from A which paints the oneway arrows
Object 3 type 0x06 derived from B
You can merge 1 with 3 because 2 will remain and will still paint the 
oneway arrows. But 1 and 3 doesn't depend on being oneway or not. This 
is interesting only for the routing layer, isn't it?

So from my point of view it should benefit more to have a look which 
operations in the filters modify the routing network and eliminate them.
This might be performed by creating a textual output of the routing 
layer. The create an output before the filters are applied and a second 
output with filters applied. Both outputs should be identical.

WanMil

> Hi,
>
> attached is a patch that should fix cosmetic issues with merge-lines and
> oneways.
>
> The idea:
> 1) merge-lines should not merge two lines if one is a oneway and one is not
> 2) merge-lines should not merge two oneway lines if the angle between
> the two ways is too small (< 30°).
> Not sure what it does with roundabouts.
>
> Please try this if your style creates overlays for oneways. I don't
> expect any changes in routing.
> Compiled version is here:
> |http://files.mkgmap.org.uk/download/123/mkgmap.jar|
>
> @Steve: Please can you check if the implemented test reg. bearings makes
> sense?
>
> Gerd
>
>
>
>
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