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<title>Coordinate Grids</title>
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<h3><img alt="" src="../sun.gif" align="middle" height="98"
width="100"> Coordinate Grids</h3>
<blockquote>
<p>DS9 can create and display coordinate grids as an overlay on an
image. The Display Coordinate Grid Menu is used to display
grids. A coordinate grid is composed of Grid Lines, Axes,
Border, and Title. Axes include tick marks, title, and numbers.
The appearance of the coordinate grid is specified by
parameters. These parameters may be configured via the
Coordinate Grid Parameters dialog box. In addition to the axes
titles and the grid title, the following menus are available. </p>
<p><b><a name="Format"></a>Numeric Formats</b></p>
<p>The user may specify custom numeric formats for either axes.
The format specification can be empty (default) or a print
function, based on the selected coordinate system:<br>
</p>
<blockquote> <tt>image</tt><br>
<tt>physical</tt><br>
<tt>detector</tt><br>
<tt>amplifier</tt><br>
<tt>wcs linear</tt><br>
<tt>wcs equatorial</tt><br>
</blockquote>
<p>The format specification string to be passed to the C "printf"
function (e.g. "%%1.7G") in order to format a single coordinate
value.</p>
<p>The Format string supplied should contain one or more of the
following characters. These may occur in any order, but the
following is recommended for clarity:</p>
<blockquote> "": Indicates that a plus sign should be prefixed to
positive values. By default, no plus sign is used.<br>
"z": Indicates that leading zeros should be prefixed to the
value so that the first field is of constant width, as would be
required in a fixed-width table (leading zeros are always
prefixed to any fields that follow). By default, no leading
zeros are added.<br>
"i": Use the standard ISO field separator (a colon) between
fields. This is the default behaviour.<br>
"b": Use a blank to separate fields.<br>
"l": Use a letter ("h"/"d", "m" or "s" as appropriate) to
separate fields.<br>
"g": Use a letter and symbols to separate fields ("h"/"d", "m"
or "s", etc, as appropriate), but include escape sequences in
the formatted value so that the Plot class will draw the
separators as small super-scripts.<br>
"d": Include a degrees field. Expressing the angle purely in
degrees is also the default if none of "h", "m", "s" or "t" are
given.<br>
"h": Express the angle as a time and include an hours field
(where 24 hours correspond to 360 degrees). Expressing the angle
purely in hours is also the default if "t" is given without
either "m" or "s".<br>
"m": Include a minutes field. By default this is not included.<br>
"s": Include a seconds field. By default this is not included.
This request is ignored if "d" or "h" is given, unless a minutes
field is also included.<br>
"t": Express the angle as a time (where 24 hours correspond to
360 degrees). This option is ignored if either "d" or "h" is
given and is intended for use where the value is to be expressed
purely in minutes and/or seconds of time (with no hours field).
If "t" is given without "d", "h", "m" or "s" being present, then
it is equivalent to "h".<br>
".": Indicates that decimal places are to be given for the final
field in the formatted string (whichever field this is). The "."
should be followed immediately by an unsigned integer which
gives the number of decimal places required, or by an asterisk.
If an asterisk is supplied, a default number of decimal places
is used which is based on the value of the Digits attribute.<br>
</blockquote>
<p>All of the above format specifiers are case-insensitive. If
several characters make conflicting requests (e.g. if both "i"
and "b" appear), then the character occurring last takes
precedence, except that "d" and "h" always override "t".</p>
<p>The default formats are <tt>d.3</tt> for degrees and <tt>hms.1</tt>
/ <tt>dms.1</tt> / <tt>ldms.1</tt> for sexagesimal.<br>
</p>
</blockquote>
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