[talk-ph] Automated assessment of OSM coastline data quality

[maning sambale]

Interesting.  Thanks for sharing Eugene.

I think the common issue for the Philippines is the third case in the
first image ("coastline with detailed but inaccurate approximation").
When we started the coastline correction 3 years ago, there was very
little hi-res imagery.  For my part, I did most of the corrections
using the Landsat imagery.  Vewing with bing's hires imagery, there is
an obvious offset from the Landsat derived correction.  As mentioned
in the article, this is not considered in the output visualization.

If we can get Cristoph's code for making this visualization, maybe we
can setup another webmap (like the Sawtooth Coastlines webmap) to
coordinate improvements?
Helping Indonesia improve its coastline is a good inter-community
project as well. :)


On Sun, Apr 14, 2013 at 3:26 AM, Eugene Alvin Villar <seav80 at gmail.com> wrote:
> Hi guys,
>
> Here's a nice analysis done by Christoph Hormann in automated assessment of
> the quality of OSM's coastline data:
> http://www.imagico.de/map/coastline_quality_en.php
>
> If you don't want to read the whole article, here's the TL;DR version:
>
>> Coastlines where there are a few nodes per kilometer AND where the angle
>> at each node is large means that the coastline is most likely to be of low
>> quality. The last map image in the article highlights areas in the world
>> where these "low" quality coastlines are located such as large parts of
>> Indonesia.
>
>
> The Philippines is on the "average" to "probably good" side of the scale. I
> think this is thanks in a large part to the coastlines correction
> collaboration the OSMPH community did 3 years ago:
> http://wiki.openstreetmap.org/wiki/Philippines/Coastline_corrections
>
> But if you look at Japan, you can see that it is on the "probably very good"
> side of the quality scale. So the Philippines still needs a lot of
> improvement.
>
> If you want to help out improving the OSMPH coastlines, you can do the
> following:
> 1. Go to the OSMPH imagery coverage map (either
> http://maning.github.io/Imagery_Coverage_Map/ or
> http://tools.openstreetmap.org.ph/imagery_coverage/ )
> 2. Look for remote/provincial coastline areas with high-res Bing satellite
> imagery
> 3. Zoom into a coastline, then switch between the Bing and OSM/MapQuest
> background layers to check the coastline accuracy
> 4. Click on the "Edit in Potlatch" or "Edit in JOSM" link to edit away! (You
> need to enable JOSM's Remote Control feature [it is enabled by default in
> newer JOSM versions] for the "Edit in JOSM" link to work.)
>
> If you're using JOSM, the Improve Way Accuracy tool
> (http://josm.openstreetmap.de/wiki/Help/Action/ImproveWayAccuracy) is
> *extremely* helpful. If will eliminate the need to click-drag your mouse.
>
> Maybe in the future, we can recreate the quality algorithm developed by
> Christoph Hormann and create a webmap specific for the Philippines. :-)
>
> Keep on mapping!
>
> Eugene
>
>
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> talk-ph at openstreetmap.org
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>



--
cheers,
maning
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