McIDAS Learning Guide
Version 2006

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Loop Control System - Creating a Loop

In this exercise, you will start a McIDAS session with six frames, display six images with the IMGDISP command and loop the frames using Alt L. Then, you will switch to the opposite loop with the Alt O command.
  1. Start a McIDAS session.
    At the Unix prompt:
    Type:  mcidas
    Your session should still be set for six frames from the last time you made changes in the Configuration GUI. If not, set it for six frames, as described in Getting Started.
  2. Log on to the workstation.
    Type:  LOGON initials project I
  3. Check the loop bounds.
    Press:  Alt F
    The default loop bounds are 1 through 3 as shown. Notice that the loop bounds in the status line is 1-3. 
        Video Status for Your Workstation
                            Frame(s)
                            --------
 Number of Available               6
 Current                           1   (Opp = 4 )
 Loop Bounds                    1 to  3
 Visible (K & W toggle)      Yes/Yes
 Looping (L toggle)               No
 Cursor parameters: Size =   31 /   31         Type = Xhair
         Center position =   10 /   10         Color = RED
 
 Image frames   1 -  6     with imbedded graphics    are  480 BY  640
  4. Display six images using the following IMGDISP commands. IMGDISP is discussed further in the Satellite Imagery lesson.
    Type:  IMGDISP GV4.1 1 STATION=DCA REPEAT=3
    Type:  IMGDISP GI4.1 4 STATION=DCA REPEAT=3
  5. Loop frames 1 through 3.
    Press:  Alt L
    Notice that the status line at the bottom of the Text and Command window changes to show an L under Switches and the Frame number changes as the loop progresses: 
     IMA GRA Bounds Switches                          Date        Time   T  
 [2] [2]  1-3       L                        23 Oct 2000297 15:43:31 0
  6. Toggle to the opposite loop.
    Press:  Alt O
    The loop displays frames 4 through 6 and the bounds in the status line changes to 4-6.

  7. Stop the loop.
    Press:  Alt L
    The loop display returns to the first frame in the current loop sequence, in this case, frame 4. Notice that the status line now has a value of 4 in the Frame position and the L is not listed in the switches section. 
     IMA GRA Bounds Switches                          Date        Time   T
   4   4  4-6                                23 Oct 2000297 15:44:01 0
  8. Toggle to the primary loop.
    Press:  Alt O
  9. Use the single letter commands A and B to manually step through the current loop. Alt A advances through the frames; Alt B moves backwards through the frames.
    Press:  Alt A
    Press:  Alt B

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