FIXED_MAP_GRID Name
FIXED_MAP_GRID Purpose
The MAP_GRID procedure draws the graticule of parallels and meridians,
according to the specifications established by MAP_SET. MAP_SET must be called
before MAP_GRID to establish the projection type, the center of the
projection, polar rotation and geographical limits.
Category
Mapping.
Calling Sequence
MAP_GRID Inputs
NONE
Optional Inputs
NONE
Keyword Parameters
BOX_AXES: Surround the map window with a "box" style axes with
annotations, outside the box, where the parallels intersect the
sides, and the meridians intersect the bottom and top edges of the
box. The border of the box is drawn in alternating foreground and
background colors, with color changes at each intersection with
a parallel or meridian. This keyword determines the thickness of
the box's border, in millimeters. If LABEL is not explicitly
specified, it defaults to 1 when this keyword is present. If this
feature is selected, be sure to leave enough room around the map
window for the annotation, usually by specifying the XMARGIN and
YMARGIN keywords to MAP_SET. See the example below.
CHARSIZE: The size of the characters used for the labels. The default is 1.
COLOR: The color index for the grid lines.
FILL_HORIZON: Fills the current map_horizon.
HORIZON: Draws the current map horizon.
INCREMENT: Determines the spacing between graticle points.
GLINESTYLE: If set, the line style used to draw the grid of parallels and
meridians. See the IDL User's Guide for options. The default is
dotted.
GLINETHICK: The thickness of the grid lines. Default is 1.
LABEL: Set this keyword to label the parallels and meridians with their
corresponding latitudes and longitudes. Setting this keyword to
an integer will cause every LABEL gridline to be labeled (i.e,
if LABEL=3 then every third gridline will be labeled). The
starting point for determining which gridlines are labeled is the
minimum latitude or longitude (-180 to 180), unless the LATS or
LONS keyword is set to a single value. In this case, the starting
point is the value of LATS or LONS.
LATALIGN: This keyword controls the alignment of the text baseline for
latitude labels. A value of 0.0 left justifies the label,
1.0 right justifies it, and 0.5 centers it.
LATDEL: The spacing in degrees between parallels of latitude in the grid.
If not set, a suitable value is determined from the current map
projection.
LATS: The desired latitudes to be drawn (and optionally labeled). If
this keyword is omitted, appropriate latitudes will be generated
with consideration of the optional LATDEL keyword. If this
keyword is set to a single value, drawn (and optionally labeled)
latitudes will be automatically generated as
[...,LATS-LATDEL,LATS,LATS+LATDEL,...] over the extent of the
map. The single valued LATS is taken to be the starting point
for labelling (See the LABEL keyword).
LATLAB: The longitude at which to place latitude labels. The default is
the center longitude on the map.
LATNAMES: An array specifing the names to be used for the latitude labels.
By default, this array is automatically generated in units of
degrees. This array can be a string array or numeric, but should
not be of mixed type. When LATNAMES is specified, LATS must also
be specified, but the number of elments in the two arrays need not
be equal. Extra LATNAMES are ignored, while LATNAMES not supplied
are automatically reported in degrees. LATNAMES can be used when
LATS is set to a single value. It this case, the LATS used will
start at the specified latitude and progress northward, wrapping
around the globe if appropriate. Caution should be used when
using LATNAMES in conjunction with a single LATS, since the
number of visible latitude gridlines is dependent on many factors.
LONALIGN: This keyword controls the alignment of the text baseline for
longitude labels. A value of 0.0 left justifies the label,
1.0 right justifies it, and 0.5 centers it.
LONDEL: The spacing in degrees between meridians of longitude in the grid.
If not set, a suitable value is determined from the current map
projection.
LONLAB: The latitude at which to place longitude labels. The default is
the center latitude on the map.
LONS: The desired longitudes to be drawn (and optionally labeled). If
this keyword is omitted, appropriate longitudes will be generated
with consideration of the optional LONDEL keyword. If this
keyword is set to a single value, drawn (and optionally labeled)
longitudes will be automatically generated as
[...,LONS-LONDEL,LONS,LONS+LONDEL,...] over the extent of the map.
The single valued LONS is taken to be the starting point for
labeling (See the LABEL keyword).
LONNAMES: An array specifing the names to be used for the longitude labels.
By default, this array is automatically generated in units of
degrees. This array can be a string array or numeric, but should
not be of mixed type. When LONNAMES is specified, LATS must also
be specified, but the number of elments in the two arrays need not
be equal. Extra LONNAMES are ignored, while LATNAMES not supplied
are automatically reported in degrees. LONNAMES can be used when
LONS is set to a single value. It this case, the LONS used will
start at the specified longitude and progress eastward, wrapping
around the globe if appropriate. Caution should be used when
using LONNAMES in conjunction with a single LONS, since the number
of visible longitude gridlines is dependent on many factors.
MAP_STRUCTURE: Set this keyword to a !MAP structure, as returned from
MAP_PROJ_INIT. If this keyword is set then the gridlines are passed
through MAP_PROJ_FORWARD and the resulting lines are drawn using
Cartesian coordinates. If this keyword is not set then it is assumed
that MAP_SET has been called to set up a map projection.
NO_GRID: Set this keyword if you only want labels but not gridlines.
ORIENTATION: Specifies the clockwise angle in degrees from horizontal
of the text baseline that the labels should be rotated. Note,
that the rotation used in MAP_SET is also clockwise, but XYOUTS
is normally counterclockwise.
T3D: Set this keyword to indicate that the generalized transformation
matrix in !P.T is to be used. If not present, the user-supplied
coordinates are simply scaled to screen coordinates.
ZVALUE: Sets the Z coordinate, in normalized coordinates in the
range of 0 to 1, at which to output the continents.
Note - This keyword has effect only if keyword T3D is set and the
transformation is stored in !P.T
Outputs
Draws gridlines and labels on the current map.
Example
map_set,10,20,23.5,/cont,/ortho,/horizon ; establish a projection
lats=[-65,-52,-35,-20,-2.59,15,27.6,35,45,55,75,89]
; choose the parallels to draw
map_grid,lats=lats,londel=20,lons=-13,label=2,lonlab=-2.5,latlab=7
;draw the grid
Make a map with a grid surrounded by a box style axis:
map_set, /STEREO, 40, -90,scale=50e6,/CONTINENTS, XMARGIN=3, YMARGIN=3
map_grid, /BOX_AXES, COLOR=3, CHARSIZE=1.5 ;
Modification History
Written by: SVP, May, 23 1996.
DMS, Feb, 1996 Note that this version plots all gridlines
unless a 4 element LIMIT was specified to MAP_SET.
SVP, Nov 1996 Changed over !map1 (new IDL5 maps)
SVP, May 1996 Map_Grid used to live inside of map_set.pro, now
it lives here.
SVP, May 1996 Changed LABEL to determine the skip between labelled
gridlines.
Also, added the LATS and LONS keywords to give complete
control over where the labels go.
SVP, Sept 1996 Added LATNAMS,LONAMES, and ORIENTATION keywords
DMS, Nov, 1996 Rev 2 of maps.
DMS, Jul, 1997 Added Box Axes
CT, Jan 2004: Added MAP_STRUCTURE keyword.
Renamed the function FIXED_MAP_GRID with fixed at lines 555-556 and
664-665 as described here: http://www.dfanning.com/map_tips/missinggrid.html.
This is required to get proper grid output in some applications, but
it breaks other code.