Charles Seaton wrote:
> I would like to use a higher resolution coastline than the high resolution
> coastline optionally provided with (specifically, I would like to use the
> NOAA/NOS Medium Resolution Coastline). I can see two ways to do this:
>
> Option 1) Create a coastline file using the in the NOAA/NOS data in the same
> format as the data files used by the basemap toolkit. I couldn't find a
> description of this format, but it appears that it is partially explained by
> the code snippet:
>
> if line.startswith('P'):
> area = float(linesplit[5])
> west,east,south,north =
> float(linesplit[6]),float(linesplit[7]),float(linesplit[8]),float(linesplit[9])
> typ = int(linesplit[3])
>
> So the first line of the existing high resolution coastline is:
> P 0 169598 1 W 79866900.000 -17.53378 190.35911 -34.83044 77.71958
>
> Which should be interpreted as
> typ = 1
> area = 79866900.000
> west = -17.53378
> east = 190.35911
> south = -34.83044
> north = 77.71958
>
> area is used to control whether this segment of coastline is displayed
> the directions are the bounding box for the coastline segment
> I am not clear on how typ is used (I see it getting manipulated, but I don't
> see it ever getting used), or what its acceptable values are. I am also not
> clear what the first, second and fourth values of the line are (not counting
> the initial 'P'). Any help with this format would be appreciated.
>
> Option 2) Load a coastline by whatever means I choose as a list of lists of
> touples (or some other format?) and then transform those values using the
> basemap object. If the coastline were easily expressed as a pair of lists or
> arrays lon,lat, then I could simply use
>
> b=basemap(...)
> coastx,coasty = b(lcoastlon,coastlat)
>
> but the coastline is made up of multiple segments (islands, etc). Is the
> best way to transform a collection of segments simply to loop over the
> segments?
>
> coast = [ [(x11,y11),... (x1n,y1n)], [(x21,y21),... (x2n,y2n)],...
> [(xn1,yn1),...(xnn,ynn)] ]
> newcoast = []
> for c in coast:
> ln,lt = map(list,zip(*c))
> x,y = m(ln,lt)
> newcoast.append(zip(x,y))
>
> Once I have a transformed list of lists of touples, I can replace the
> basemap objects coastsegs
> b.coastsegs = newcoast
>
> and then draw the coastline using the built-in
> b.drawcoastlines()
>
> Or is there some method that I am missing?
>
>
>
Charles: If you can get the coastlines in a shapefile, that's probably
the easiest way to do it. See the fillstates.py example for reading in
and plotting shapefiles on maps.
-Jeff
--
Jeffrey S. Whitaker Phone : (303)497-6313
NOAA/OAR/CDC R/PSD1 FAX : (303)497-6449
325 Broadway Boulder, CO, USA 80305-3328
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