not an idea - but a comment. I think that for such a special nonusual
case, there should be no degradation for the general use. Wouldn't it be
enough to just switch off douglas peucker algo for maps where you want
to include long "straigt" lines?
On 25.07.2014 10:46, Gerd Petermann wrote:
Hi Roger,
the problem is caused by the routine that removes obsolete points from
straigt lines.
This routine doesn't care (enough) about the spherical distortian.
The routine uses herons formula to "calculate distance of point in the
middle to line c1,c2".
This formula is for 2D, but used to work good enough with the rather
short ways
we have in OSM. (The formula is also used in the Douglas-Peucker filter).
With long lines the as in your data, the errors are too big and the
routine returns garbage.
If I got that right, we have to use the formula for the "Cross-track
distance" as described here:
http://www.movable-type.co.uk/scripts/latlong.html
Unfortunately, this routine uses more trigonometrical calculations, so
it will be slower.
@Programmers: Any other ideas?
Gerd
------------------------------------------------------------------------
Date: Wed, 25 Jun 2014 12:12:18 +0100
From: [email protected]
To: [email protected]
Subject: [mkgmap-dev] Incorrect compilation of grid lines
I have a file containing the British National Grid lines, as printed
on Ordnance Survey maps. This can be found at
http://www.rogercalvert.me.uk/osm/GBGrid/GBGrid.zip (this contains two
files, they are the same except for the addition of the 'version' tag
in the GBGrid06.osm file). I compile this file with mkgmap and overlay
it on my GPS map.
This works correctly with mkgmap 2654 and It displays correctly in JOSM.
With mkgmap version 3241, the lines are misaligned and out of
position. The behaviour is the same on MapSource, BaseCamp and my
device. No error messages are produced.
(I have not used any versions of mkgmap in between these two).
My style file allocates codes in the 0x10300 range to these lines, but
the effect is the same when I use code 0x21 (contour) for all lines.
Attached are screen dumps for a small part of the map, from JOSM,
mkgmap 2654 and mkgmap 3241, and also the batch file I used to compile it.
I would greatly appreciate any advice.
Many thanks,
Roger
--
------------------------------------------------------------------------
Roger Calvert
http://www.rogercalvert.me.uk
------------------------------------------------------------------------
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--
keep on biking and discovering new trails
Felix
openmtbmap.org & www.velomap.org
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