Re: orthographic projection

[Patrick Joeckel <joeckel@xxxxxxxxxxxxxxxxx>]

----------  Forwarded Message  ----------
Subject: Re: orthographic projection
Date: Tue, 08 Aug 2000 10:55:09 -0700
From: Jonathan Callahan <callahan@pmel.noaa.gov>


Patrick,

Yes, there is a problem with some of the map projections when
encountering the edges of a longitude axis even though it is defined as
modulo.  This simple work around is to use region qualifiers to force
Ferret to draw over the region that wasn't drawn properly the first
time.  I've added two lines that will get you the output you want. 
Additions to your script are marked with "HERE >"


-- Jonathan Callahan

Patrick Joeckel wrote:
> 
> Dear Ferreters,
> 
> below I included a script which uses the orthographic projection for plotting
> data. Two problems occur:
>  1) go mp_land plots the map on top, however with a gap where the underlying
>      lon-axis (defined with modulo) wraps around
>  2) the interpolation with "fill" exhibits a discontinuity at the same meridian
>      (take a look over Europe !!!)
> 
> Are these problems known to anyone, and does possibly a workaround exist ?
> Hope anybody can help me !
> 
> Best regards ...
>           Patrick Joeckel
> 
> --------------------------------------------------------
> cancel data/all
> cancel variable/all
> cancel region
> 
> define axis/x=1.875:358.125/npoints=96/unit=lon/mod xax
> define axis/y=-90:90:10/unit=lat yax
> define grid/x=xax/y=yax g2d
> 
> let one = x[gx=xax]+y[gy=yax]
> let data = COS((5*x[gx=xax]/180)*3.1415+1)*SIN((Y[gy=yax]/180)*3.1415)
> 
> ppl shaset 0 100 100 100
> 
> set grid g2d
> go mp_orthographic 0 90
> go mp_aspect
> 
> fill data*mp_mask, x_page, y_page
HERE > fill/over/x=90w:90e data*mp_mask, x_page, y_page
> 
> go mp_graticule 0 360 10 -90 90 30 5
> 
> go mp_land 13 " " 1 1
HERE > set region/x=90w:909e
HERE > go mp_land 13 " " 1 1
> 
> --------------------------------------------------------
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