Cursoring
Cursoring |
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Simply click on the trace you wish to cursor. The cursor will move to the
trace you clicked on and that trace will become active. The x and y-cursor edit
boxes will change to the color of the new active trace and those edit boxes will
be updated to contain the current x and y locations of the cursor. Although the
color of the edit box will often be enough to let you know which trace is active it
sometimes may be difficult to tell at a glance if there are many traces plotted.
For this reason a cursor ID tag is displayed just to the left of the
y-cursor edit box. This will be especially helpful if you assigned meaningful
trace names in the plt calling sequence. This cursor ID tag is also in the same
color as the active trace.
Click on a trace, hold down the mouse button and drag the cursor left or right. The cursor will follow the mouse as you are dragging and the edit boxes will continually update with the current cursor location. Make sure you click directly on the trace. If you are not close enough to the trace, when you drag the mouse the x and y axis limits will pan to follow the mouse movement.
If you type a new value into the x-cursor edit box, the cursor will move to (x,y) where x is the value you typed in, and y is the value of the active trace at location x. (i.e. the cursor will remain on the active trace). However if you type a new value into the y-cursor edit box, the cursor will move up or down (off the trace) to the location (x,y) where x is the old cursor x position, and y is the value you typed in.
In
the lower left corner of the display you will find the cursor peak/valley
buttons (up and down arrows) as well as the delta cursor button. (Delta cursors
are described below.) When you click
on the up arrow (peak finder) button, the cursor will move to the largest peak in the
current display range of the active trace. The next click on the up arrow will move
the cursor to the second largest peak and so on. Moving the cursor by clicking
on the trace or by using the cursor slider will reset the peak finder so that the next time
you click on the up arrow the cursor again moves to the largest peak in the
display range. An alternate way to reset the peak finder is to right
click on the peak finder button. The valley button works the same as the peak button except the
cursor moves to successive local minima.
If the string
'Slider'
or
'S' appear in the
'Options'
argument then this slider is inserted just below the peak/valley/delta buttons
shown above. This slider has two different functions depending on whether the x
axis has been expanded.
If the x axis has not been expanded (or has been expanded by less than a factor of two) then this slider moves the cursor left or right by 1% of the data length when you click on the left or right slider arrows and left or right by 5% of the data length when you click in the trough area of the slider to the left or right of the slider button. The slider button itself is not used in this mode and remains fixed in the middle of the slider.
If the x axis has been expanded (by more than a factor of two) then this slider makes it easy to quickly scroll thru the data set or to pan to a particular location. Clicking on the left or right arrows moves the view window left or right by 10% of the visible range i.e. currently visible data will be scrolled out of view after 10 clicks. (Holding the mouse button down over these arrows results in a pleasing continuous scrolling effect.) Clicking in the trough area to the left or right of the slider button moves the view window left or right by 100% of the visible range (i.e. currently visible data will be scrolled out of view for every click). Note that the slider button moves to show the relative position of the data currently in view. Also you can do a quick pan by grabbing the slider button with the mouse and dragging it left or right. Dragging it as far as possible to the left or right causes the plot to pan to the beginning or end of the data and dragging it near the center of the slider pans the plot to show data near the middle of the data set. Note that all three panning methods (arrow, trough, button) keep the amount of data displayed constant (i.e. the difference between the upper and lower x-axis limits doesn't change). The data cursor is kept in the middle of the x-axis during this type of panning.
When the data density is high (i.e. a long vector is plotted) it can be difficult to move the cursor by the smallest amount possible (i.e. one data element) by dragging the cursor with the mouse, so an alternate method is provided for this. Simply click on the x-axis label (for example "Milli-seconds" in the plot below) and the cursor will move forward by one data element. And a right click will move in the reverse direction. This method of moving the cursor also proves useful when it is difficult to see the data ordering (unconnected markers for instance).
When you right click on the y-axis label, the menu box and all cursor objects disappear. This is useful for making screen captures of the plots since these objects are used for data exploration and are normally just a distraction in a hardcopy. Right clicking again causes the objects to reappear. (The plt hideCur; command has the same effect.)
Delta cursors are useful for measuring horizontal or vertical distances between two points on a trace. First move the cursor to the desired reference point on the trace. Then press the Delta (∆) cursor button. The reference location will be marked with a large red plus (about 4 times bigger than the normal cursor). Also the Delta cursor button will be highlighted as an additional reminder that delta cursors are enabled. Next, click on a different point on the same trace (or drag the cursor to the desired location). The view will then look similar to the picture shown here. (You can also click on a point on a different trace -- the delta cursor will still work as expected.) You can read the current location of the cursor (the small yellow plus) in the usual way - i.e. the edit boxes just to the right of the grey x/y labels. In this case the cursor x location is 5.75 msec and the y location is 0.377755. The other two edit boxes show how far away the cursor is from the marked reference. In this example, it shows that the cursor at a location 1.55 msec later than and .37885 units less than the marked reference. Simply click on the delta cursor button again, and the reference mark will disappear, the delta cursor button returns to its normal color, and the usual cursor operation will return.
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When you click on the cursor ID tag (Line 4 in this example) the ID tag changes to Avg and the edit box then shows the average y-value of all the points of the active trace that are within the current display x limits.
When you click on the ID tag a second time, the Avg changes to RMS and the edit box then shows the rms value of the active trace. As with Avg, the rms calculation only includes points that are within the currently displayed x-axis limits. (In case you are not familiar with this commonly used form of averaging - rms stands for "root mean square" and is calculated by taking the square root of the average of the squares of the data values).
When you click on the ID tag a third time, the RMS changes to Y/X and the value in the y-cursor edit box changes to show the ratio of the y and x cursor values at the current cursor position (i.e. the slope of the line from the origin to the cursor). If delta cursors were enabled, and additional edit box appears to the right of the y-cursor edit box. This additional box contains ΔY/ΔX, which is the slope of the line connecting the marked position to the current cursor. You can use this to estimate the slope of a trace at a particular point.
Clicking the ID tag a fourth time (or clicking in the plot area) restores the cursor readout to show the usual Y value and the ID tag again shows the name of the cursored trace.
The usual cursor can show the value of only one of the visible traces on the plot. With a dual cursor, two such values can be shown at the same time. This is especially useful when displaying two tightly linked values (for example, the magnitude and phase of a complex quantity). You specify a dual cursor for the Nth trace by including 'DualCur',N in the parameter list. This means that trace N will never be the active trace and so its value will never appear in the usual y value readout location (immediately to the right of the "y:" cursor label). However when you cursor any other trace, the value of trace N will appear just to the right of the value for the active trace. (Note - this is the same readout location used for delta cursors). In the plot area, the dual cursor appears on the chosen trace along with the usual cursor on the active trace.
This example was created by including 'DualCur',1 in the parameter list so that the first trace (green in this example) is always cursored along with the active trace. In this picture, Line 2 (purple) has been selected as the active trace (by clicking on it) and so its y value is shown (also in purple) in the usual y-readout location. As you move the active cursor back and forth along the x-axis, the dual cursor on trace 1 (the asterisk) tracks the back and forth movement and the Line 1 y-value is shown in the green edit box. The dual cursor is easily distinguished from the usual cursor by its shape - an asterisk if the dual cursored trace is on the left axis or a square if it is on the right axis. (See the next section for a discussion of the right hand axis.)
A complication happens when you are using the dual cursor and delta cursor features at the same time, because the same auxiliary y readout location is used for both features. The conflict is resolved as follows ... If you click directly on a trace, the delta cursor value is displayed. If you click anywhere else on the plot, the dual cursor value is displayed. It is easy to tell which value is displayed because two x cursor values are displayed in delta cursor mode whereas only one x cursor value appears in dual cursor mode.
When using subplots, the full cursoring features described above apply only the main (lower left) plot. The cursoring features that are only available on the main plot are:
Each subplot however has its own y-axis cursor readout. These cursor readouts are easy to identify since its background color matches the trace and axis colors. Also the full panning and zooming features of plt are supported for each subplot. For dual column subplots, moving the cursor left and right by left/right clicking on the x-axis label (as described above) works independently for the two columns as you would expect.