Ross Beyer PIRL, LPL
rbeyer@lpl.arizona.edu September 1999
Pixelito will read in a TIFF image, and knowing the direction
that the sun is coming from in the image, will allow the
user to select a point, and then draw a line in the down-sun
direction. The user can then either plot up the DN values
of the pixels along the line, or run a very rough photoclinometry
algorithm on the line.
How to run Pixelito
Be running IDL 5.2 or later. Make sure that you have the
FETCH_FIELDS DLM module written at PIRL. Then at the
IDL prompt, just type `pixelito' .
TIFF selection window
When you run pixelito it will bring up a file selection window
where you should enter the name of the TIFF file to be read in.
Data entry
After you have selected the file, Pixelito needs other information.
You can either enter the information by hand, or if the image is a
MOC image that has been released via the PDS, then Pixelito can
get the information for you. The MOC image name entry is case
insensitive, but must be of the form phase name (AB-1, M2) - orbit
number (then a slash for AB and SPO or a dash for all later phases),
and then image number. For example: AB-1-080/03, spo-2-252/03, or
M2-0002-00001.
Sun Angle
This value is an angle where zero is directly to the
right of the image and increases CLOCKWISE. If the
sunlight were coming from the top of the image,
sun_angle=270.
Incidence Angle, Emission Angle, Resolution
If you are not going to be using the photoclinometry
option, you can just hit `enter' in these fields.
Pixelito Main Window
This window displays the image that Pixelito read in, and
the option buttons.
Snap to/Drag
This button tells the cursor how to behave. When
set to `Snap to' it will draw the line from the
point that you left-click the cursor. When set
to `Drag' it will clicking and releasing the mouse
will drag the line around the image.
Line Length
The length of your line, in pixels.
Display DN values along this line
This will bring up a plot window of the DN values
along the line that you have selected.
Print DN to postscript file & an ASCII list
This will write out two files: an ASCII list of
the X and Y coordinates of the pixels in your
line along with their DN values, and a postscript
Plot of DN values along the line that you have
selected (identical to the above option).
Do photometry on this line
This will read the DN values along the line and
invoke a very simple photoclinometry algorithm
based on techniques from Squyres (1981,
Icarus 46, p.156). It computes the surface slopes
for each image element. It also goes on to plot a
profile of heights based on those slopes. This
code can be found in `showsl.pro' part of the
Pixelito routines.
NOTE: This algorithm is very rough, and rather
full of errors, use with extreme care (or not at
all).
Print Slopes & Heights to postscript file & an ASCII list
This will write out two files also. The first is
an ASCII list of the X and Y coordinates of the
pixels in your line along with their computed slopes,
distance along line in resolution units and height
above the first point in resolution units. The
second is a Postscript plot of the profile (idenical
to the above option).
Write Image
This allows you to write out the image with the line
plotted out on it, either as a GIF or a TIFF.
Close
This closes and exits Pixelito.
Last modified: 13 SEP 99