diff options
Diffstat (limited to 'ds9/doc/user/contour/thread.xml')
| -rw-r--r-- | ds9/doc/user/contour/thread.xml | 258 |
1 files changed, 258 insertions, 0 deletions
diff --git a/ds9/doc/user/contour/thread.xml b/ds9/doc/user/contour/thread.xml new file mode 100644 index 0000000..48d4d32 --- /dev/null +++ b/ds9/doc/user/contour/thread.xml @@ -0,0 +1,258 @@ +<?xml version="1.0" encoding="us-ascii" ?> +<!DOCTYPE thread> + +<thread> + + <info> + + <version>June 2009</version> + <title> + <long>Contours</long> + </title> + <history> + <entry day="24" month="June" year="9" who="liz"> + Original version + <!-- copied in part from CIAO ds9 thread //--> + </entry> + </history> + </info> + + <text> + <overview> + + <synopsis> + <p> + Contours are shapes which are drawn on the data at a + specified pixel value. ds9 can create and display contours + as an overlay on an image. + </p> + </synopsis> + </overview> + + <sectionlist> + + <section id="create"> + <title>Creating Contours on a Dataset</title> + + <p> + This thread uses Chandra data from an observation of the + galaxy cluster Abell 2142 (ObsID 5005). + </p> + + <p> + After loading the data into ds9 and setting the desired + scale, click on the "Contours" item in the "Analysis" menu + to turn on contour display. Open the "Contour Parameters" + window from "Analysis → Contours Parameters". There + are two sliding scales which are used to set the number and + smoothness of the contours and fields for setting the range + of values to use. + </p> + + <figure id="dialog"> + <title>Contour Parameters dialog box</title> + <description>The "Contour Parameters" dialog box has sliding + scales to set the number and smoothness of the contours and + fields for setting the range of values.</description> + <bitmap format="png">dialog.png</bitmap> + </figure> + + <p> + Typically, you will want to generate between 1 and 10 + contours; larger numbers will take longer to generate and + display. A smoothness level of 1 will evaluate the contour + at each image pixel, while a level of 2 will evaluate the + contour at every other pixel, and so on. A larger smoothing + will generate contours more quickly, but less detail will be + available. + </p> + + <p> + By default, the range of the data scale is filled in as the + limits. Under the "Method" menu, there are two choices: + </p> + + <list type="1"> + <li> + block (the default) - blocks down the image by the + smoothness factor before contours are calculated. The + larger the smoothness, the faster the result. + </li> + + <li> + smooth - smooths the image before calculating contours. + The larger the smoothness, the slower the result. + </li> + </list> + + <p> + In this example, the number of levels is set to 6 and the + smoothing is set to 5. The contours will be generated over + the limit 1 to 100. The default method (block) is used. + </p> + + <p> + After clicking the "Generate" button, the list of contours + is calculated and displayed in the "Levels" portion of the window. + Click "Apply" and the ds9 display is updated with the new + contour levels, as shown in <figlink id="xraycontour"/>. + </p> + + <figure id="xraycontour"> + <title>X-ray data with contours</title> + <description>Diffuse emission with + contours overlaid; a point source is visible in the upper + left corner of the image.</description> + <bitmap format="png">xraycontour.png</bitmap> + </figure> + + <p> + The contour parameters can be adjusted until the desired + result is achieved. Be sure to click "Generate" whenever + an adjustment is made so that the levels are recalculated. + </p> + + </section> + + <section id="copy"> + <title>Copying the Contours to Another Frame</title> + + <p> + In this section, we take the X-ray contours just generated + and display them on an optional image from the Digital Sky Survey (DSS). + </p> + + <p> + From the "Analysis → Image Servers" menu, select one + of the DSS server options (e.g. "SAO-DSS"). The server + dialog box allows you to retrieve an optical image of the + field of your observation and load it into a new frame. The + default retrieval image size and (RA,Dec) is equal to the + size and center of the field currently displayed. Here the + width and height have been set to 40, but the (RA,Dec) + determined by ds9 are used. + </p> + + <figure id="dssdialog"> + <title>SAO-DSS Server dialog box</title> + <description>The fields for Ra, Dec, width, and height are + populated with values determined from the x-ray data image.</description> + <bitmap format="png">dssdialog.png</bitmap> + </figure> + + <p> + Click on "Retrieve" and the data is loaded into a new ds9 + frame. + </p> + + <p> + To copy the x-ray contours: + </p> + + <list type="1"> + <li><p> + Select the frame with the X-ray data in it. + </p></li> + <li><p> + Use "Frame → Match Frames → WCS" to align the + two images. + </p></li> + <li><p> + To copy the contours, open the "Contour Parameters" + dialog again and select "Copy Contours" from the + "File" menu. Leave the window open, as it is needed in + a future step. + </p></li> + <li><p> + Select the frame with the optical data in it. + </p></li> + <li><p> + Using the "File" menu of the "Contour Parameters" + dialog, select "Paste Contours". + </p></li> + <li><p> + Adjust the parameters (if desired) in the small dialog box + that is displayed, then click "OK". + </p></li> + </list> + + <p> + The optical image now has the x-ray contours overlaid. + Since the WCS is the same, correlation between x-ray + and optical features may be seen. + </p> + + <figure id="dsscontour"> + <title>X-ray and optical data with contours</title> + <description>The x-ray data is in the left frame and the + optical data is in the right frame; both have the x-ray + contours displayed on the data.</description> + <bitmap format="png">dsscontour.png</bitmap> + </figure> + + <p> + To delete contours which have been pasted into a + frame, select "Clear" from the "File" menu of the "Contour + Parameters" dialog. + </p> + + </section> + + <section id="save"> + <title>Saving the Contours</title> + + <p> + To save the contours to a text file, choose "Save Contours" + from the "File" menu of the "Contour Parameters" dialog. + The contours are saved in a text file which can be loaded + back into ds9 with the "Load Contours" menu item. + </p> + + <p> + The contours generated in this thread have been saved as <a href="ds9.con">ds9.con</a>. + </p> + + </section> + + <section id="convert"> + <title>Converting to Polygons and Saving</title> + + <p> + The contours can be converted to ds9 polygon regions for use + in filtering data. Converting to polygons also allows you + to select and/or delete specific contours. + </p> + + <p> + <strong>Note that the contours cannot be <threadlink id="save">saved + in ds9 format</threadlink> after converting.</strong> If you wish to + save the contours, do so before continuing. + </p> + + <p> + To convert the contours, select "Convert to Polygons" from + the "File" menu of the "Contour Parameters" dialog. The + contours are now defined as ds9 polygons, e.g. + </p> + +<screen> +polygon(3535.2112,4184.5,3540.5,4179.1154,3548.5,4176.8219,3555.9012,4184.5,3548.5,4191.9558,3540.5,4190.3926) +</screen> + + + <p> + The polygon-shaped contours can be saved as a ds9 region + file from the "Region Save → Regions" menu. The region + file for these contours has been saved as <a href="a2142.reg">a2142.reg</a>. + </p> + + </section> + + + </sectionlist> + </text> + +</thread> + + + |