| Coastal boundaries over sat data [message #21224] |
Wed, 16 August 2000 00:00  |
Daniel Peduzzi
Messages: 29
Registered: June 1999
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Junior Member |
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I have some satellite imagery in its native projection (DMSP,
GOES, Meteosat, and GMS) with accompanying latitude/longitude
pairs for each pixel. I'd like to display these images in their
native projections using 0-100% grayshades, but overlayed with
coastal boundaries in some non-grayshade color.
Is this possible using the standard map routines available in
V5.2? I've found plenty of ways to draw boundaries over data
which have been remapped to some other projection, but not in
the raw satellite projection.
Alternatively, does somebody have a routine to do this?
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Dan Peduzzi
peduzzi@mediaone.net
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| Re: Coastal boundaries over sat data [message #21551 is a reply to message #21224] |
Wed, 30 August 2000 00:00  |
Sylvain Carette
Messages: 19
Registered: May 2000
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Junior Member |
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<tt>Interesting thread</tt><tt></tt>
<p><tt>There is a small application with source code (in Delphy - kind
of OO Pascal)</tt>
<br> <a href="http://www.davidtaylor.freeserve.co.uk/software/hrpt.htm">HRPT
programs - from David Taylor, Edinburgh</a>
<br><tt>It doesnt display continent outline but it can "rectify" the image
which might be the projection you are looking for. The code is well commented
and readable even for a non-pascal programmer (like me - but I'm used to
C so its similar).</tt><tt></tt>
<p><tt>It may or may not be pertinent for your need since it remap the
data - not a real projection, a rectification or an unwrapping of the data.</tt>
<br><tt>On my side, I need to use that kind of rectification applied along
the path of the satellite to build continuous "ribbon" of avhrr data. Maybe
this could be somewhat applied to your case; instead of applying a projection
on the image array, you proccess each line separately as is it were a whole
image and reset the projection for each line and appending all the lines
together.</tt><tt></tt>
<p><tt>If the only thing you want is to overlay the continent outline over
the "natural" data, I think I would consider the problem as applying a
*warping* to the outline derivated from the lat/lon values contained in
the data instead of using map projection.</tt><tt></tt>
<p><tt>Hope this could be of some help</tt><tt></tt>
<p><tt>Sylvain Carette</tt>
<br><tt>VRML designer-composer</tt><tt></tt>
<p><tt>Ben Marriage wrote:</tt>
<blockquote TYPE=CITE><tt>Daniel Peduzzi wrote:</tt>
<br><tt>></tt><tt></tt>
<p><tt>> Thanks...that is a handy program, and I've used it before in the
past.</tt>
<br><tt>> I'm not sure that it can be used for what I want to do, though,
since</tt>
<br><tt>> I don't want to remap the data...only display it in its *native*</tt>
<br><tt>> projection with coastal boundaries.</tt>
<br><tt>></tt>
<br><tt>> In other words, if I have 1000 scanlines of DMSP data (1465 elements</tt>
<br><tt>> wide), and accompanying 1465x1000 lat/lon arrays, I'd like to
display</tt>
<br><tt>> a 1465x1000 image overlaid with coastlines.</tt><tt></tt>
<p><tt>I did something like this to check if an AVHRR pixel was over land
or</tt>
<br><tt>not.</tt>
<br><tt>I'll post the code here in case you are interested. I had to create
an</tt>
<br><tt>image which consisted of 0s and 1s corresponding to sea and land.
I did</tt>
<br><tt>this from IDL using map_set and map_continents (filling it as color=1),</tt>
<br><tt>then tvrd() and saving into a format handy format (in this case,
idl</tt>
<br><tt>save format) You could try doing it without filling, just keeping
the</tt>
<br><tt>continent outline in a file. I then have to restore this file each
time</tt>
<br><tt>I need to check for land. This is fairly resolution dependent,
but works</tt>
<br><tt>OK for me (AVHRR data around Antarctica).</tt><tt></tt>
<p><tt>It's a rather quick and dirty method - but *it works for me*(TM)</tt><tt></tt>
<p><tt>Ben</tt>
<br><tt> ;=========================================================== ================ </tt>
<br><tt>function landmaskcheck, lats, longs</tt><tt></tt>
<p><tt>; land_mask.idl is an image which has a 0 over the sea and a 1 over</tt>
<br><tt>; land. This was produced from a 2048x2048 window and using the</tt>
<br><tt>; map_set and map_continents procedures to define areas of land
and sea.</tt>
<br><tt>; Then, using the convert_coord function we convert latitudes and</tt>
<br><tt>; longitudes to land mask subscripts to determine if that pixel
is over</tt>
<br><tt>; land.</tt><tt></tt>
<p><tt>sizeimg = size(lats)</tt><tt></tt>
<p><tt>; this file contains 0s and 1s corresponding to sea/land.</tt>
<br><tt>; restoring this file creates an IDL variable called MASK</tt><tt></tt>
<p><tt>restore,file='~/cloudcl/data/land_mask.idl'</tt><tt ></tt>
<p><tt>; open up a new window</tt><tt></tt>
<p><tt>oldwin = !D.window</tt>
<br><tt>window,xs = 2048,ys=2048,/pix,/free</tt>
<br><tt>newwin = !d.window</tt><tt></tt>
<p><tt>; setup the map reprojection used to create the land mask file initially</tt><tt></tt>
<p><tt> map_set,-90,0,0,/ster,/noborder,xmarg=0,ymarg=0,limit=[-30,- 90,-45,0,-80,90,-55,-135],/iso </tt><tt></tt>
<p><tt>; convert the input image longitudes and latitudes to device coordinates</tt>
<br><tt>in</tt>
<br><tt>; the new reprojection</tt><tt></tt>
<p><tt>sub = convert_coord(longs,lats,/data,/to_device)</tt><tt></tt>
<p><tt>; squish them to the right size</tt><tt></tt>
<p><tt>xsub = reform(sub[0,*],sizeimg[1],sizeimg[2])</tt>
<br><tt>ysub = reform(sub[1,*],sizeimg[1],sizeimg[2])</tt><tt></tt>
<p><tt>; this bit produces an image (same size as the input) which contains
a 1</tt>
<br><tt>over</tt>
<br><tt>; land and a 0 over the ocean</tt><tt></tt>
<p><tt>flag = mask[xsub,ysub]</tt><tt></tt>
<p><tt>wdelete,newwin</tt>
<br><tt>wset,oldwin</tt><tt></tt>
<p><tt>return,flag</tt><tt></tt>
<p><tt>end</tt>
<br><tt> ;=========================================================== ================= </tt></blockquote>
<tt></tt></html>
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