In article <MPG.16a6689c231416089897c5@news.frii.com>, david@dfanning.com wrote:
> Kenneth Bowman (k-bowman@null.com) writes:
>
>> If the finished "thing" (I avoid the word object) is to be 2-D, try the
>> SATELLITE projection in MAP_SET.
>>
>> If you want a 3-D "thing", you could do a CYLINDRICAL EQUIDISTANT plot
>> with MAP_SET. CONTOUR will return the coordinates of the isopleths
>> (PATH_INFO, PATH_XY). Then transform the longitude-latitude coordinates
>> into 3-D space and use direct or object graphics to display the resulting
>> lines.
>
> Somehow I knew the answer to this was going to be easy. :^)
Oh, its not nearly as hard as object graphics. Here is a direct graphics
example.
Note that the work of extracting the contour lines and converting to
Cartesian coordinates is only a few lines of IDL code.
I leave it to you object wizards to turn the 3-D lines into objects and stick
a sphere object inside. ;-)
Ken
PRO SPHERICAL_PLOT
COMPILE_OPT IDL2
cr = ''
nx =
65
;Grid resolution in longitude
ny =
33
;Grid resolution in latitude
x =
(360.0/(nx-1))*FINDGEN(nx)
;Longitude grid
y = -90 +
(180.0/(ny-1))*FINDGEN(ny)
;Latitude grid
xx = x # REPLICATE(1.0,
ny) ;2-D longitude grid
yy = REPLICATE(1.0, nx) #
y ;2-D latitude grid
z = SIN(!DTOR*xx) *
COS(!DTOR*yy) ;Test function to
contour
;Standard contour plot on satellite map projection
MAP_SET, /SATELLITE, /CONT, /ISOTROPIC
CONTOUR, z, x, y, LEVELS = -0.95 + 0.1*FINDGEN(20),
/OVERPLOT ;Contour z
PRINT, 'Enter <cr> to continue.'
READ, cr
;Get contour info
CONTOUR, z, x, y, PATH_INFO = path_info, PATH_XY = path_xy,
$ ;Contour z, save contour info
/PATH_DATA_COORDS, CLOSED = 0, LEVELS =-0.95 + 0.1*FINDGEN(20)
;2-D plot using contour info
PLOT, [0, 0], [1, 1], /NODATA, $
XTITLE = 'Longitude', $
XSTYLE = 1, $
XRANGE = [0.0, 360.0], $
XTICKS = 4, $
YTITLE = 'Latitude', $
YSTYLE = 1, $
YRANGE = [-90., 90.0], $
YTICKS = 6
FOR k = 0, N_ELEMENTS(path_info)-1 DO BEGIN
i0 =
path_info[k].offset
;First element of the k'th contour
i1 = i0 + path_info[k].n -
1 ;Last element of the k'th
contour
; PRINT, k, path_info[k].type, i0, i1
xc =
REFORM(path_xy[0,i0:i1])
;Extract x-coords of k'th contour
yc =
REFORM(path_xy[1,i0:i1])
;Extract y-coords of k'th contour
IF (path_info[k].type EQ 1) THEN
BEGIN ;Close contours, if needed
xc = [xc, path_xy[0,i0]]
yc = [yc, path_xy[1,i0]]
ENDIF
PLOTS, xc,
yc ;Plot
contours
ENDFOR
PRINT, 'Enter <cr> to continue.'
READ, cr
;3-D plot using contour info
PLOT_3DBOX, [0,0], [0,0], [0,0], /NODATA, $
XTITLE = 'X', $
XSTYLE = 1, $
XRANGE = [-1.0, 1.0], $
XTICKS = 4, $
YTITLE = 'Y', $
YSTYLE = 1, $
YRANGE = [-1., 1.0], $
YTICKS = 4, $
ZTITLE = 'Z', $
ZSTYLE = 1, $
ZRANGE = [-1.0, 1.0], $
ZTICKS = 4
r = 0.9
FOR k = 0, N_ELEMENTS(path_info)-1 DO BEGIN
i0 =
path_info[k].offset
;First element of the k'th contour
i1 = i0 + path_info[k].n -
1 ;Last element of the k'th
contour
; PRINT, k, path_info[k].type, i0, i1
xc =
REFORM(path_xy[0,i0:i1])
;Extract x-coords of k'th contour
yc =
REFORM(path_xy[1,i0:i1])
;Extract y-coords of k'th contour
IF (path_info[k].type EQ 1) THEN
BEGIN ;Close contours, if needed
xc = [xc, path_xy[0,i0]]
yc = [yc, path_xy[1,i0]]
ENDIF
x3 = r * COS(!DTOR*yc) *
COS(!DTOR*xc) ;Convert to Cartesian
coordinates
y3 = r * COS(!DTOR*yc) * SIN(!DTOR*xc)
z3 = r * SIN(!DTOR*yc)
PLOTS, x3, y3, z3, /T3D
ENDFOR
END
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