Well Landsat's resolution is low so any coastline traced using Landsat (like almost all of the coastline corrections 3 years ago) will have a low average distance between nodes marking it as low to average quality. So while the offset may be a problem, I think the low node density can be already used as a flag for coastlines that still need improvement.
On Mon, Apr 15, 2013 at 10:28 AM, maning sambale <[email protected] > wrote: > 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 <[email protected]> > 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 > > > > > > _______________________________________________ > > talk-ph mailing list > > [email protected] > > http://lists.openstreetmap.org/listinfo/talk-ph > > > > > > -- > cheers, > maning > ------------------------------------------------------ > "Freedom is still the most radical idea of all" -N.Branden > wiki: http://esambale.wikispaces.com/ > blog: http://epsg4253.wordpress.com/ > ------------------------------------------------------ >
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