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

[maning sambale]

The top ten islands is almost complete (not in the mandelbrotian sense).

I added a new list of coastline bounty in the wiki (11-30 largest islands)
http://wiki.openstreetmap.org/wiki/WikiProject_Philippines/Coastline_Corrections#Priorities

Please edit the status as you start working on each island.

Note that some have a 99% status already, but, it is good for other
eyeballs to have a look and comment on the actual %age and status.

On Wed, Jul 7, 2010 at 2:03 AM, Eugene Alvin Villar <seav80 at gmail.com> wrote:
> On Tue, Jul 6, 2010 at 2:42 PM, Jim Morgan <jim at datalude.com> wrote:
>>
>> Eugene Alvin Villar wrote, On Tuesday, 06 July, 2010 11:57 AM:
>> > 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
>>
>> There are a number of cases where a near-straight line is acceptable.
>> Maybe it would be better -- and I'm not sure if this is possible -- to
>> examine, say, a series of three nodes. It would check if the first two have
>> the same lat or long. If they have the same lat, then the second and third
>> points would need the same long; if they have the same long, then the second
>> and third points would need the same lat. Then you'd be correctly
>> identifying the step-fashion jaggies, rather than straight lines.
>>
>>
>> To increase certainty, you could make this a series of four, or five
>> points. Again I don't know if this is possible or plausible, but it would
>> seem like a better pattern to look for. Not sure if the formatting will come
>> through but ....
>>
>>
>>  p1 |_____ p2
>>          |
>>          |
>>       p3 |______  p4
>>                 |
>
> I intentionally wanted to detect collinear nodes since I wasn't sure if the
> original SRTM-based data have those collinear nodes or not.
>
> In any case, the script detects sawtooth coasts if the latitude or the
> longitude is *exactly* the same, right down to the 7th decimal place (which
> translates to an accuracy of about 1 cm). So if there are a series of
> coastline nodes that have the same latitude or longitude for each adjacent
> pair of nodes, then they are most likely generated from raster data, like
> SRTM. I don't think Mother Nature created coasts that follow latitudes and
> longitudes. :-)
>
>
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>



-- 
cheers,
maning
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