The Tracking Error Graph is a graphical presentation of the most recent 1 to 15 minutes of guiding errors. You can choose to display the errors in either or both axes, expressed in either the camera (X–Y) or telescope (RA–Dec) frame of reference. In addition either RMS Trends or markers indicating when corrections were commanded can be displayed. The data can be plotted against time, with the graph auto-scrolling toward the left when it fills up, or as a scatter plot of Y errors against X errors. The vertical scale and time duration of the graph are selectable. The peak excursion and current RMS value of each error are displayed at the bottom of the graph for quick reference.
The Tracking Error Graph window can be adjusted to any desired size using the mouse; the graph automatically stretches or shrinks to fill it.
Tracking errors are always collected whether this window is active or not, so you can turn it on to check for guiding anomalies if you suspect one has occurred based on inspection of a main camera image.
Please note that the graph shows the instantaneous measurements of guider offset, not the actual tracking of the mount itself. If you set the Aggressiveness to a low value, such as 2 to 4, the mount will effectively be following a “rolling average” of the current and recent guider measurements. In that situation, you may see a large scatter on the graph due to seeing, but the actual guiding performance could be several times better than indicated by that scatter. Of course this only works if the “real” errors are slow enough to be tracked out with a low aggressiveness.
All options are selected from the menu at the bottom left corner of the window.
The Plot submenu
contains commands to select what is plotted. Choose Camera
Axes or Telescope Axes
depending on whether you want to see the guiding errors as measured
in the camera frame of reference, or as rotated to the telescope frame.
The latter setting can be useful when determining if poor guiding
results from a mechanical problem in the telescope mount.
Please note that the default setting of Telescope Axes means the graph display will likely not match the error display on the Guide tab. This is normal, and is more informative than displaying camera coordinates because the autoguider camera may be rotated relative to the telescope mount axes.
Select X Error to plot the error in the X axis (dark green) against time, Y Error for that in Y (dark blue), X and Y Errors to superimpose both on one graph, or X and Y (separate) to display them in separate graphs within the same window, as shown above. Select X–Y Scatter Plot to plot Y error against X error.
Select Show RMS Trends to display the root-mean-square error as well as the instantaneous error. The RMS error is a moving average of the measurements made over an adjustable interval called the RMS Window, discussed below. RMS Trends are shown in a lighter color than the raw measurements. They are not available when X and Y Errors are plotted on the same graph.
Show Corrections draws special "boxed" markers to indicate where MaxIm DL's autoguiding logic corrected the tracking. When the graph mode is X Error, Y Error or X and Y (separate), the position of the marker indicates the magnitude of the correction using the alternate vertical scale at the right end of the plot. In the other modes, the boxed marker is plotted either on the line (see next) or replacing the usual marker for a measurement on that axis. Correction markers and RMS Trends are mutually exclusive, except in X–Y Scatter Plot mode.
Select Lines if you want the tracking graphs to be shown as lines. Breaks in the line shows periods when guiding was stopped or the guide star was not detected. Turn off Lines if you want the graphs to be plotted with symbols at each measurement. Small triangles are used for raw error measurements, and plus signs for RMS averages. Diamond symbols are used in scatter plot mode.
The Vertical Scale submenu allows you to select whether tracking errors and trends are displayed in pixels or in arc seconds, and the range of the Y axis (±0.5, ±1, ±2, ±5, ±10, or ±20). You must have specified the guider telescope focal length on the Site and Optics dialog and connected to the autoguider before selecting ArcSec for the first time. Thereafter MaxIm DL uses the most recent conversion factor if the autoguider is not connected.
The Time Span submenu allows you to select how much data is plotted in the graph, based on a time range ending at or near the time of the most recent measurement. The available choices are 1, 3, 6, 10, and 15 minutes. Data is not lost when the selected Time Span is shortened, only when the data point ages beyond the maximum limit of 15 minutes.
The RMS Window submenu allows you to specify the length of time over which data is averaged when computing the RMS error. You can choose between 30 seconds, 1, 2, 3 or 4 minutes. RMS information is not plotted for a measurement if there is insufficient data in the interval of this duration immediately preceding it.
NOTE: if RMS always shows N/A then you need to adjust RMS Window. If you are using long guider exposures you may need to increase the RMS Window, or you will not get enough samples to calculate an RMS value. A minimum of 8 samples is required; for example, if you have a 30 second window and use 6 second guide exposures, you will never get an RMS value. In this case you need to increase the RMS Window.
Plot type, Vertical Scale, Time Span, and RMS Window length can be adjusted at any time and the display is automatically updated.
The Peak Values submenu allows you to specify whether the extrema displayed in the status area at the bottom of the graph Reset Automatically, as soon as the peak data point is no longer displayable, i.e., is 15 or more minutes older than the most recent point, or are Reset Manually, on user command. When in manual reset mode, use the Reset Now command to reset the peak display to zero. As new measurements are made, the peak values will creep upwards.
Click Save Data to record the available measurements to a disk file. This calls up a file selector dialog with which you navigate to the desired destination folder and specify a filename. The file is written in the same format as the Tracking Log.
Click Load Data to load and display a previously saved graph or a Tracking Log. (Tracking Logs exceeding 15 minutes in duration are automatically clipped. If necessary, you can divide them into shorter segments with any text editor.) If you start the guider after loading a file, old data will be automatically flushed as soon as the first measurement is made.
The Clear Graph command erases all data from the graph. If the guider is active, the next measurement made will begin a new graph, resetting the reference time shown in the window title to the current time.