[talk-ph] better ways to coordinate coastline mapping?

Eugene Alvin Villar seav80 at gmail.com
Tue Jul 6 05:00:27 BST 2010


Anyway, it seems that Negros is actually the "cleanest" large island in
terms of coastlines. :-)


On Tue, Jul 6, 2010 at 11:57 AM, Eugene Alvin Villar <seav80 at gmail.com>wrote:

> To clarify things, the sawtooth detection script is quite naive. It simply
> detects if there are at three or more series of nodes where each pair of
> adjacent nodes have the same latitude or longitude. This will also detect
> any three linear nodes that all have the same latitude or longitude like
> this: o----o----o  (A bit silly, I know, but the middle node should probably
> be deleted anyway.)
>
> The idea of the webmap is to highlight where there are coastlines derived
> from the raster SRTM data. 99% of our coastlines were derived from SRTM and
> any "sawtooth" is an indication that this should be cleaned up to better
> match the actual coastline (like Landsat or PGS).
>
> It's ridiculously easy to defeat the script: just nudge nodes. But the
> point is not to defeat the script but to check out areas in need of
> correction. I would assume that anybody moving coastline nodes would do so
> to correct or refine the data and not simply to defeat the script, right?
> Right? :-D
>
> Another clarification, the webmap is still just an initial map and it
> doesn't currently do any updates (so maning's recent work on Mindanao's
> eastern coast won't be picked up yet). I'm working with maning to devise a
> way to have the map update on a near-daily basis by tying into his OSM-PH
> Garmin Maps workflow. Wait in the future for this.
>
>
>
>
> On Tue, Jul 6, 2010 at 10:17 AM, Ed Garcia <eppgarcia at gmail.com> wrote:
>
>> Ah I get it ... So it detects node strings that form a "step" (a
>> horizontal and a vertical combination).  It may be good to make mappers
>> aware that such a combination will trigger sawtooth detection by Eugene's
>> script.  For there are some coastline contours that are indeed on a step
>> shape.  Good way to avoid it is to move the nodes just a bit so the
>> longitude/latitude pairings would not be exactly the same.  I found this out
>> on one of my Marinduque island edits.
>>
>> thanks!
>>
>>
>>
>> On Tue, Jul 6, 2010 at 9:31 AM, maning sambale <
>> emmanuel.sambale at gmail.com> wrote:
>>
>>> @ ed,
>>> The technique is outlined here:
>>>
>>> http://wiki.openstreetmap.org/wiki/Talk:WikiProject_Philippines/Coastline_Corrections
>>>
>>> Couple of suggestions:
>>> 1. short link to the coastline correction wikipage
>>> 2. enable link to editors only at higher zoom level (perhaps 15-17?)
>>> 3. should be an osm-ph image of the week
>>>
>>> On Tue, Jul 6, 2010 at 9:20 AM, Ed Garcia <eppgarcia at gmail.com> wrote:
>>> > Wow! amazing ... how do you detect "sawtoothness"?  can you teach this
>>> at
>>> > the skillshare?  OSM genius ka talaga!
>>> >
>>> > Anyway, I take note of the sawtooth patterns between Lucena and
>>> Pagbilao
>>> > Quezon ... I have corrected this already but the sawtooth appears only
>>> on
>>> > higher zoom-out levels now.  Does this mean it is good as "done" now?
>>> It
>>> > still appears on yoursawtooth_coastlines map though.
>>> >
>>> > ed
>>> >
>>> > On Tue, Jul 6, 2010 at 1:04 AM, Eugene Alvin Villar <seav80 at gmail.com>
>>> > wrote:
>>> >>
>>> >> HI guys,
>>> >>
>>> >> Here's an *initial* webmap showing where the jagged coastlines are as
>>> of
>>> >> July 3:
>>> >> http://forge.codedgraphic.com/osm/sawtooth_coastlines/
>>> >>
>>> >> The larger the circle, the more jagged steps there are to clean up.
>>> >>
>>> >> Sorry, there's no link going to Potlatch or JOSM/Merkaartor. I'll add
>>> that
>>> >> up when I learn more of OpenLayers. But for now, this will have to do.
>>> >>
>>> >> Enjoy!
>>> >>
>>> >> Eugene
>>> >>
>>> >> On Mon, Jul 5, 2010 at 9:30 AM, maning sambale
>>> >> <emmanuel.sambale at gmail.com> wrote:
>>> >>>
>>> >>> We missed the June target to to finish the 10 largest islands.
>>> >>>
>>> >>>
>>> http://wiki.openstreetmap.org/wiki/WikiProject_Philippines/Coastline_Corrections#Priorities
>>> >>>
>>> >>> That's OK.  All we need is to finish mainland Mindanao and we can set
>>> >>> our radar to the next 20 on the list.
>>> >>> We are also working on some webmap to visualize the "sawtooth".  More
>>> >>> on that when its ready.
>>> >>>
>>> >>>
>>> >>> On Sun, Jul 4, 2010 at 5:48 PM, maning sambale
>>> >>> <emmanuel.sambale at gmail.com> wrote:
>>> >>> > I can load it in my public dropbox.
>>> >>> >
>>> >>> > On Sun, Jul 4, 2010 at 2:23 PM, Eugene Alvin Villar <
>>> seav80 at gmail.com>
>>> >>> > wrote:
>>> >>> >> Hi guys,
>>> >>> >>
>>> >>> >> Once we are done with the large islands, the next step is to do
>>> the
>>> >>> >> smaller
>>> >>> >> islands. Ian Haylock has helpfully provided the PGS coastlines[1]
>>> for
>>> >>> >> the
>>> >>> >> Philippines last year[2] which he edited to combine ways. PGS
>>> itself
>>> >>> >> was
>>> >>> >> automatically generated by a software by analyzing the Landsat
>>> >>> >> imagery.
>>> >>> >> Unfortunately, Ian's file was hosted on a free file server and has
>>> now
>>> >>> >> expired but I think several people on the mailing list managed to
>>> >>> >> download
>>> >>> >> it.
>>> >>> >>
>>> >>> >> I tried opening the file last year in Merkaartor but my old laptop
>>> >>> >> couldn't
>>> >>> >> handle the data. Now that I have a 4GB-RAM laptop, loading the
>>> data
>>> >>> >> into
>>> >>> >> Merkaartor is very manageable. Using the PGS coastlines is much,
>>> much
>>> >>> >> easier
>>> >>> >> than tracing Landsat by hand. I tried this with Homonhon Island
>>> and
>>> >>> >> editing
>>> >>> >> is way faster than actually uploading it[3]. Hehehe. What I did
>>> was to
>>> >>> >> delete the SRTM-derived coastline[4] and replace it with the PGS
>>> >>> >> coastline[5].
>>> >>> >>
>>> >>> >> I think uploading the PGS coastlines is better for the smaller
>>> >>> >> islands. I'll
>>> >>> >> see what we can do to have the PGS coastlines (55MB) uploaded
>>> >>> >> somewhere.
>>> >>> >>
>>> >>> >> [1] http://wiki.openstreetmap.org/wiki/Prototype_Global_Shoreline
>>> >>> >> [2]
>>> >>> >>
>>> http://lists.openstreetmap.org/pipermail/talk-ph/2009-June/001071.html
>>> >>> >> [3] http://www.openstreetmap.org/browse/changeset/5129873
>>> >>> >> [4] http://www.openstreetmap.org/browse/way/4327906
>>> >>> >> [5] http://www.openstreetmap.org/browse/way/65592780
>>> >>> >>
>>> >>> >> Eugene
>>> >>> >>
>>> >>> >>
>>> >>> >> On Thu, Jun 17, 2010 at 8:20 PM, maning sambale
>>> >>> >> <emmanuel.sambale at gmail.com>
>>> >>> >> wrote:
>>> >>> >>>
>>> >>> >>> UPDATE. Only two islands from the top ten need some coasty
>>> coastline
>>> >>> >>> love.
>>> >>> >>>
>>> >>> >>>
>>> >>> >>>
>>> http://wiki.openstreetmap.org/wiki/WikiProject_Philippines/Coastline_Corrections
>>> >>> >>>
>>> >>> >>> Anyone working on Negros and Mainland Mindanao?
>>> >>> >>>
>>> >>> >>
>>> >>> >>
>>> >>> >
>>> >>> >
>>> >>> >
>>> >>> > --
>>> >>> > cheers,
>>> >>> > maning
>>> >>> > ------------------------------------------------------
>>> >>> > "Freedom is still the most radical idea of all" -N.Branden
>>> >>> > wiki: http://esambale.wikispaces.com/
>>> >>> > blog: http://epsg4253.wordpress.com/
>>> >>> > ------------------------------------------------------
>>> >>> >
>>> >>>
>>> >>>
>>> >>>
>>> >>> --
>>> >>> cheers,
>>> >>> maning
>>> >>> ------------------------------------------------------
>>> >>> "Freedom is still the most radical idea of all" -N.Branden
>>> >>> wiki: http://esambale.wikispaces.com/
>>> >>> blog: http://epsg4253.wordpress.com/
>>> >>> ------------------------------------------------------
>>> >>>
>>> >>> _______________________________________________
>>> >>> talk-ph mailing list
>>> >>> talk-ph at openstreetmap.org
>>> >>> http://lists.openstreetmap.org/listinfo/talk-ph
>>> >>
>>> >>
>>> >>
>>> >> --
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>>> >>
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>>> >
>>> >
>>> >
>>> > --
>>> > website administrator:
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>>> > - reeflife.eppgarcia.com
>>> >
>>> > PADI Divemaster #491048
>>> >
>>>
>>>
>>>
>>> --
>>> cheers,
>>> maning
>>> ------------------------------------------------------
>>> "Freedom is still the most radical idea of all" -N.Branden
>>> wiki: http://esambale.wikispaces.com/
>>> blog: http://epsg4253.wordpress.com/
>>> ------------------------------------------------------
>>>
>>> _______________________________________________
>>> talk-ph mailing list
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>>
>>
>>
>> --
>> website administrator:
>> - www.waypoints.ph
>> - reeflife.eppgarcia.com
>>
>> PADI Divemaster #491048
>>
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>
>
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>



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