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<title>Contour Creation</title>
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<h1>Contour Maps</h1>
<P> Selecting <B>Make Contour Map</B> from the <B>Edit</B> menu brings
up a dialog box which allows one to specify how the contour map will
be created for the current image in the current graph (indicated by
the green bounding box)...</P>
<BLOCKQUOTE>
<P> <B>Image Range</B>: Minimum and maximum pixel values of the
selected image.</P>
<P> <B>Contour Range</B>: Minimum and maximum values to contour over.
The values are initially taken from a "clean" approximation of the min
and max pixel values of the image, but the user can change these
values to whatever is desired. (Note that the min value need not be
less than the max value.)</P>
<P> <B># Contours</B>: Number of contour levels to produce between the
range points. One can either click on the <B><</B> or <B>></B>
buttons to decrease/increase the number or type in a new number
directly.</P>
<P> <B>Scale</B>: Scaling method for interpolating contour levels.
The <B>linear</B> method will space the contours over a constant
interval from the min and max range. The other two options -- sqrt
and log -- do much the same thing but based on the square root or
logarithm of the min and max values. These latter options bring out
the finer details at the lower contour levels in images with a large
dynamic range. </P>
<P> <B>Contours</B>: This is the actual list of contours to draw. The
previous contour items update this list each time they are clicked,
but the list may be customized prior to clicking the <B>Make Contours</B>
button.
<P> <B>Resolution</B>: This determines how detailed (and accurate) the
contours will be. At high resolution, contours will be produced based
on the value from each pixel of the image. Low resolution will
produce contours using the average pixel value in 3x3 sections,
resulting in a lot few points to be plotted and, therefore, faster
performance. Medium resolution uses 2x2 sections. Using high
resolution when the contour intervals are similar in size to the image
noise will create an enormous number of points, significantly slowing
down POW.</P>
<P> <B>Separate Graph</B>: If this box is checked, when the contours
are created, the contours will be placed in a separate graph by
itself. Otherwise, the contours will be placed on top of the current
graph along with the original image.</P>
</BLOCKQUOTE>
<P> Click on the <B>Make Contours</B> button to build and draw the
contours. After a set of contours is created, its parameters can
still be modified in this dialog box and the contours recreated
(replacing the previous version) with the <B>Make Contours</B> button.
Contours are created as a POW curve, so one can control its display
features (color, line style, etc) from the <A
href="EditGraphs.html">Edit Graphs</A> dialog box.</P>
<P> If the original image contains <B>WCS</B> information, the
contours will be created in terms of celestial coordinates. (Without WCS
information, contours will be drawn in pixel coordinates.) As a
result, one can place the contours made from one image into a graph
containing another image (with its own, possibly different, WCS
information) and the contours will be positioned appropriately for the
new graph. This can be used to compare observations of the same
object at different wavelengths (eg, radio and optical).</P>
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