[talk-ph] On editing PH coastlines

Ed Garcia eppgarcia at gmail.com
Fri Apr 10 06:08:28 BST 2009


I have also been doing "coastal cleanup" lately.  Main reason being that
since I use OSM map tiles for waypoints.ph and since a lot of our
destination waypoints are near the coasline (beaches and island destinations
are the most popular), I wanted to have good coastline detail on OSM and
correct those current "sawtooth" coasts.

Most interesting to clean up is the area around west Batangas, especially
north Nasugbu which have dozens of mini peninsulas and promontories.  They
are interesting to look at now (on Osmarender for now as Mapnik may still
take time to update the coasts)

http://openstreetmap.com/?lat=14.1316&lon=120.6185&zoom=13&layers=0B00FTF

I did encounter similar concerns as Maning had too regarding mangroves and
wide rivers.  I am more particularly concerned if the landsat is actually
accurate enough for mapping smaller details such as rivers ... similar
problem with Yahoo imagery on Makati as reported earlier on another
discussion.

Just recently, we took tracks and points on the Mangrove Project of
Sariaya.  We particularly and specifically navigated the wide river that
divides the mangrove area and the tracks were taken with a GPS276C with
external antena on the boat and had more than 8 satellites in view (very low
position error).  Now, when the tracks were superimposed on JOSM against the
WMS landsat image, the river was off by as muchg as 50 meters!   I just went
ahead and used the GPS tracks instead of the landsat image for plotting the
river:

http://openstreetmap.org/?lat=13.82952&lon=121.46565&zoom=15&layers=B000FTF

As what really to follow as "coastline", my opinion is to make existing
structures or natural "protrusions" as the coastline.  Not knowing what to
really follow earlier, I looked at what was done to represent the coastline
on the Manila Bay and Malabon area and I see that the coastline was traced
along the piers and man-made "land" areas.  So, I guess that will do well
for showing piers / wharfs / mangroves /very wide beaches / tidal lands.

:>) ed


On Fri, Apr 10, 2009 at 11:46 AM, Maning Sambale <emmanuel.sambale at gmail.com
> wrote:

> Hi,
>
> Since my etrex GPS died,  I have resorted to coastline mapping to
> improve previous coastline import.  I have completed several islands
> already and my next target is Luzon mainland (already completed most of
> north-east Luzon up to Ilocos Sur).  At first, I thought it should be
> easy, just load LANDSAT WMS and your good to go.  But really it isn't.
>
> Because,
>
> 1) coastline is a fractal problem [1], at varying zoom-levels you get
> different details.  Using landsat, you need to be at zoom 14-16 to get
> the most detail.
>
> 2) I find it difficult to select, move, and delete nodes of the SRTM
> generated coastline.  You have to use several keystrokes and
> mouse-clicks.  What I do instead is delete several coastline ways and
> then create a new coastline way.
>
> Some questions:
>
> 1) How do we map mangrove [2] areas along coastlines?  In the "field"
> mangroves are either inland extending to the coast and even beyond
> coastline.  Do we include mangroves in inter-tidal areas as part of the
> coastline?
>
> 2) Where do coastline and large rivers converge?  River deltas [3] is
> particularly problematic.
>
> 3) Sand bars? Siltation areas?  Any suggestions on how we map this?
>
> Me thinks: coastlines will never be complete because we have so much
> coastline and the threat of sea-level rise due to climate change
>
>
>
>
> [1] http://library.thinkquest.org/26242/full/ap/ap4.html
> [2] http://en.wikipedia.org/wiki/Mangroves
> [3] http://en.wikipedia.org/wiki/River_delta
>
> --
> 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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