MAG_GRID
Name
MAG_GRID
Purpose
Return a magnetic grid warped to the current map projection,
that can be overlayed on an image.
Category
SNOE, image, mapping
Calling Sequence
result = mag_grid()
Inputs
NONE
Optional Inputs
NONE
Keyword Parameters
HIRES: Set this keword equal to one (1) to produce a high
quality grid. This may take some time (less than a
minute). The default is a low quality (but quick)
image
MAGTHICK: Set this to the line thickness desired.
OVAL: Set this to the thickness desired for the auroral oval
grid lines (i.e. the 60 and 70 degree latitude lines)
LATDEL, LONDEL: See MAP_GRID documentation
Outputs
This function returns a bytescaled image. The size is the size
of the current device. The array returned contains the value 1
where the field lines are, and 0 everywhere else.
Side Effects
NONE known
Restrictions
Must call map_set before this function
Requires mag_grid.pro
Procedure
This function warps a CGM magnetic lookup table (LUT) onto the
current map projection. Since our LUTs are at a 1 degree
resolution, the quality of the lines is poor. Hence the /HIRES
keyword. The algorithm is the same in this case, but the image
is created much larger (approx 20 times), and then shrunk
down. The result is a higher quality image.
Example
;;; set up and display the data
MAP_SET, 88.5, 277.5, /cyl, /iso
TV, MAP_IMAGE( data, xx, yy ), xx, yy
img = TVRD()
;;; get the grid for the above map_set projection
grid0 = MAG_GRID()
grid1 = MAG_GRID( /HIRES, YEAR=2000, magthick=2, oval=4 )
;;; overlay grid on image, and display
magGridColor = 255
img[ WHERE( grid1 EQ 1 ) ] = magGridColor
TV, img
Modification History
Written by: Ted Fisher, Summer 2000
Oct, 2001 TAF: made lots of misc usability improvements
Oct, 2001 KDM: added documentation, removed xysize
Jul, 2002 KDM: Removed YEAR keyword. LOAD_CGM has
own. Uses _EXTRA=e