 News |
FAQ
|
| Search
|
Home
|
| Getting Started | Documentation | Glish | Learn More | Programming | Contact Us |
|
| Version 1.9 Build 1556 |
|
Here is a detailed description of the option record elements. This is based on how they appear in the Adjust.. GUI sorted by context.
These are the options available to raster, contour and vector Viewerdisplaydatas. Jump to display type specific options:
In this roll-up, adjustments can be made to select how the data is sliced for display, i.e. which axes of the data are mapped to X and Y on the screen. As well, a third axis (where appropriate) can be assigned to the Z (or movie) axis, which is the data axis along which progressive frames will be shown when a Viewerdisplaypanel is playing a sequence of frames. The new selection will not take place until the Apply button at the bottom of the adjustment window is pressed. If you have accidentally selected the same axis for more than one display axis, then this will be indicated by red crosses, and you should correct your error, and press Apply again.
This roll-up is only present when the image or array has more than three axes, and is used to set the location in the data along all of the axes which are not mapped to either X, Y or Z (movie) axes in the Display axes roll-up. Simply sliding any of the scales should result in immediate updates to any Viewerdisplaypanel on which this Viewerdisplaydata is registered.
Note: For measurement sets, these sliders are incorporated into the Display axes rollup.
In this roll-up, adjustments can be made to how the coordinates under the pointer (mouse cursor) are displayed.
By default, position tracking is enabled, so that as your move the pointer over the display, the data value and coordinate are shown in the status line beneath the display. This information will be displayed on any Viewerdisplaypanel on which this Viewerdisplaydata is registered.
You can turn position tracking off with the switch called Position Tracking? at the bottom of the rollup.
Position tracking can also be turned on for all Viewerdisplaydatas registered on a single Viewerdisplaypanel by pressing the t key, and turned off by pressing Shift-t, while the pointer is hovering over the particular Viewerdisplaypanel.
Other options in this rollup are
You may display absolute or relative (to the reference pixel) coordinates. This switch toggles between the two.
You may display world or pixel coordinates. This switch toggles between the two.
A data lattice is discrete, but each pixel can be considered to extend
over the range i
0.5. E.g. pixel [20,30] in a 2D images
covers the range [19.5,29.5] to [20.5,30.5]. By default
pixel coordinates are presented integrally. If you like, this
optional allows you to have them presented fractionally.
If the data contain a spectral axis, this menu will be included. It allows you to select the units for the presentation of the spectral coordinates (e.g. km/s or Hz etc). Conversion to km/s is only possible if the Spectral coordinate contains the rest frequency. In its absence, no conversion to km/s will be offered. You can set the rest frequency with the coordsys.setrestfrequency function.
If the data contain a spectral axis, this menu will be included. If you ask to see the spectral coordinate as a velocity, then this allows you to select the type of velocity definition (e.g. optical, radio etc.).
The parameters in this roll-up offer basic control over the axis labels (which by default are not visible). To turn them on, select True for Axis labelling & annotation. The other parameters in this roll-up are pretty much self explanatory, and include text entries for the axis labels (unset will give reasonable defaults in most cases), and control of whether tick marks or grid lines are drawn.
In this roll-up, finer control over the axis label properties is provided.
Here you have control over whether the axis labels are shown as world coordinates or image pixel coordinates (1-relative). You may select whether the labels are relative (to the reference pixel) or absolute.
For Direction coordinates, you may select the units of the labels if they are relative. For Spectral coordinates you may select the units of the labels, and the velocity type. For other Coordinate types, you don't yet have further control over the units.
You can also choose the Direction coordinate reference type of the following J2000, B1950, GALACTIC, ECLIPTIC and SUPERGAL. Your coordinate grid will reflect these types.
You can also choose where to place your axis labels. The default Auto is usually sufficient, but other placements are available.
Colors can be selected for various elements of the labelling, and the character font and size can be chosen. It is generally recommended to first select character font and size, and then pop on over to the Canvas Manager (available under the File menu of the Viewerdisplaypanel) to finely tune the positioning of the displayed image on the Viewerdisplaypanel. In a future release of AIPS++, this geometry adjustment will be automatic.
This option controls the dimensions with which data pixels are drawn to the screen. Fixed lattice means data pixels will be mapped to square pixels on the screen, in as much as the screen pixels themselves are square. Fixed world means that the aspect ratio of the pixels according to the coordinate system of the image will be honoured. Finally, selecting flexible will allow the raster map to stretch independently in each direction to fill as much of the Viewerdisplaypanel as possible. The default setting is fixed world.
This option controls how individual data pixels are drawn to the screen. Selecting center means that pixels at the edge of the display will be drawn only from the centres inwards. That is, down the left hand border of the raster map, only the right-hand half of the pixels will be visible, and along the bottom of the raster map, only the upper half of the pixels will be visible. So for center, the raster map is drawn from the center of the bottom left pixel in the selected data to the center of the top right pixel in the selected data.
Selecting edge (the default) will change this behaviour such that all data pixels will be drawn fully on the screen. This would be useful for cases where only one of the display axes only has length one pixel.
This setting controls how the data are resampled to the resolution of the screen. The default, nearest, means nearest neighbour resampling, whereby each pixel on the screen is colored according to the intensity of the nearest corresponding data pixel. The alternative, bilinear, applies a bilinear interpolation to produce smooth-looking images independent of the screen pixel dimensions of the data pixels. While bilinear resampling normally produces a better looking image, it can be significantly slower than nearest neighbour resampling, so be aware of this.
If the data source (image or array) is Complex, then this menu allows you to select whether you wish to see the magnitude, phase, real or imaginary part.
This region entry is only available for raster maps of images, and allows the selection of a particular part of the image for display. A region can be placed in the region entry, and the easiest way to do this is to bring up the Regionmanager using the spanner menu to the right of the entry. Simply create a region with the Regionmanager, and send it to this control by pressing Send or Send & dismiss in the Regionmanager.
This entry is only available for raster maps of images, and allows you to specify a Boolean expression mask which is applied On-The-Fly (OTF). Thus you can apply an extra mask to the image in addition to its current persistent default mask.
The syntax is that of the Lattice Expression Language and use of the mask expression entry widget is equivalent to use of the mask keyword that is available in many Image tool functions and provides an OTF mask capability. See note 223 for details on LEL. Also see the Image tool and the Image Analysis chapter of this document for extra information.
For example, let us say you have an image on disk called 3c273.im and you have made a raster display of it with the Viewer. You then decide to mask the image as bad where all pixels are negative. You could do this with the Image tool function calcmask which would calculate and store a new mask for you. But perhaps you want to try several different masks before making one persistent. In this case, in the entry widget, you would enter the same expression that you would have provided to calcmask.
'3c273.im' > 0
and the display would be updated so that all non-negative pixels are good and all negative pixels are bad (masked). Thus, where the expression is True, the pixels are displayed. (Note: use the image filename, rather than the name of any image tool you have created, in these expressions).
When you use the Mask expression in combination with an Image region, the mask expression is applied first, and then the region. This means the shape of the mask expression must match that of the image being displayed.
Also note that if the image you are displaying has an underlying pixel mask (see the Images module), then the final mask that is applied is the union of that mask and the mask expression.
Finally, There is one important difference between using the expression mask entry widget and the mask keyword in Image tool functions. With the Image tool, you can embed Image tool names in your expressions. However, when you use the mask expression entry widget in the adjustment GUI, you must always refer to the image disk file name. You cannot use the Image tool name.
Now to the raster specific options.
Display a color wedge (bar). Note: In RGB mode the wedge isn't supported yet. The wedge will align itself to the image only if you set Basic Settings - Aspect Ratio to flexible, or the displaypanel is resized to fir the new aspect. The orientation of the wedge can be changed in the viewercanvasmanager.
The axis label to show on the wedge. The default unset shows the brightness unit if available.
Color of the axis label text.
Size of the axis label text in terms of pgplot character height.
The (pgplot) font to use for the label.
This option is specific to raster maps, and controls whether the pixel intensities for this Viewerdisplaydata are mapped to colors selected from a colormap (chosen elsewhere in the adjustment panel), or are instead mapped to one of the following color channels: red, green, blue, hue (color), saturation (color strength) or value (brightness). Use of any color mode requires that the Viewerdisplaydata be registered on a suitable Viewerdisplaypanel. That is, color mode colormap rasters must be registered on an Index Viewerdisplaypanels, color mode red, green or blue rasters will only draw when registered on RGB Viewerdisplaypanels, and color mode hue, saturation and value rasters will only draw when registered on HSV Viewerdisplaypanels.
You can use the type in entry box provided to set the minimum and or maximum data values being mapped to the colormap. Additionally, the limits can be set graphically by using the histogramgui window. This can be opened by selecting 'Histogram' from the spanner menu. For very high dynamic range images, you will need to type in a number much less than the maximum to see the low-level brightness pixels.
The default value for this option is False. When enabled for raster maps, some internal optimisation of colors from the colormap (or color channel) is made. The number of colors allocated to a given range of data is proportional to the fraction of pixels whose pixel intensities lie in that range. Thus color cells are allocated where they are needed most.
This option offers further control over the mapping of data values to color cells from the colormap. The overall process in selecting a color for a particular pixel is as follows: the data value of the pixel is clipped lie between the data minimum and maximum as specified elsewhere in this Basic settings roll-up. Then, according to this option which is described below, this clipped pixel intensity is mapped to an index between 0 and the number of colors available in the selected colormap. The color which is in the colormap at this position, which itself is controlled by the current stretch, shift, contrast, brightness and invert settings of the colormap, is then drawn for this particular pixel.
So, the scaling power cycles option controls the mapping of clipped pixel intensities to color look-up values. When this is set to zero, a straight line connects (domainMin, rangeMin) and (domainMax, rangeMax) on a plot where the domain is the input data values constrained to the range given by the data min and max sliders, and the range runs from 1 to number of colors in the selected colormap. See for sample curves.
As the scaling power decreases from zero, the curve deviates from the straight line, rising above it, such that an increasing fraction of the available colormap is used for data values close to the data minimum. This curve is calculated using a log function.
As the scaling power increases from zero, the curve deviates from this straight line, falling below it, such that an increasing fraction of the available colormap is used for data values closer to the maximum. The curve is calculated using an exponential function. 1.1
You can select a range of different colormaps here. Selections here only take effect if the color mode option is set to colormap.
You can choose to have a color bar (wedge) displayed next to your data. At the moment the wedge can be placed to the right-hand side of the image. Note: In RGB mode the wedge isn't supported yet. The wedge will align itself to the image only if you set Aspect Ratio to flexible.
Following are the contour specific options.
This option is simply where you enter the levels at which you would like contours to be drawn. There are two main ways to enter contour levels:
The contour levels given will be multiplied by the factor entered in this option before being drawn.
This option indicates whether the vector of contour levels, specified in the Contour levels box, multiplied by the scale factor, are absolute levels (that is, in the native units of the image), or are instead fractional levels, where 0 is mapped to the lowest pixel intensity in the image, and 1 is mapped to the highest.
This option controls the thickness of the contour lines. While only integer values will show any effect on-screen, PostScript output will be affected by the fractional part of the line width.
Set this option to True if you would like contours of negative values in your data to be dashed rather than solid lines.
Set this option to True if you would like contours of positive values in your data to be dashed rather than solid lines.
Select a color for the contours.
Now to the vector specific options
Vector map adjustments are based on those Basic settings. The following options are not available: resampling mode, complex mode and data minimum & maximum. In their place, the following options are added in the Basic settings section:
If the data source is Complex (z = R + iI) this option is available. It is a menu with two values: values normal and polarimetric mean the phase (position angle) is computed from atan2(I, R) and atan2(I, R)/2, respectively. The latter is appropriate when the Complex data holds, say, the Complex linear polarization z = Q + iU which has a two-fold symmetry. The default is polarimetric.
If the data source is Complex, this option allows you to discard the amplitude information and show all vectors with equal length.
If the data source is Complex (
z = R + iI) this option is available.
The default is no debiasing. The amplitude is computed from
. Now if the real and imaginary parts are
drawn from independent gaussian variables (as is the case for the
Complex polarization z = Q + iU), then even in the absence of
signal, the mean amplitide is positive. This is noise bias. This
option attempts to remove it to first order via
amp = 
.
To do this, you need the variance of the noise (assumed the same for real and imaginary). See the next option.
If the data source is Complex, this option is available. It is only
used if the debias option is selected (see above). The debiasing
is accomplished via
amp = . By
default, the variance is worked out for you from the image (the real and
imaginary 10-sigma clipped variances are worked out separately and
averaged). However, even though a clipping algorithm is used, the
variance may not be accurate. If you know the variance of the noise
accurately, enter it here.
By default, the amplitudes of the vectors are scaled so that the longest vector is of length 5% the length of the smallest display window dimension. This is an extra scale factor that you can apply to all the vectors to make them longer or shorter.
By default, vectors are displayed for every third pixel in x and y. You can change that with these options.
You can add an extra rotation (degrees) to the position angles here (e.g. to show a magnetic field position angle from electric field vectors).
This option allows you to put arrow heads on the vectors. However, if the Phase type is Polarimetric arrow heads are not displayed (two-fold symmetry makes them meaningless).
This option allows you to change the arrow head shape from a triangular head (value 0) to an open head. In between, you get 'barbed' shaped heads.
This option controls the thickness of the vector lines. While only integer values will show any effect on-screen, PostScript output will be affected by the fractional part of the line width.
Select a color for the vectors.
Now to the marker specific options
Marker map adjustments are based on those Basic settings. The following options are not available: resampling mode, complex mode and data minimum & maximum. In their place, the following options are added in the Basic settings section:
By default, the marker shape is a square. At present, this is the only marker shape available.
By default, the amplitudes of the shapes are scaled so that the width of the shape 5% the length of the smallest display window dimension. This is an extra scale factor that you can apply to all the shapes to make them bigger or smaller.
By default, markers are displayed for every third pixel in x and y. You can change that with these options.
This option controls the thickness of the marker outline. While only integer values will show any effect on-screen, PostScript output will be affected by the fractional part of the line width.
Select a color for the marker.
Skycatalog Viewerdisplaydatas are different from the others since they don't carry a coordinate system. Therefore the option record looks quite different.
This option should rarely need to be adjusted, especially for catalog overlay Viewerdisplaydatas. The value of this option specifies how many different views of the catalog overlay are stored in a cache, and can therefore be redrawn quickly on demand. A different view is generated when one or more options are altered.
This roll-up provides options for selecting which column is used to label the sources, and for setting the properties of the labels themselves.
This option must be changed from <none> if you want labels to appear next to the source markers. Select the column which contains the names; the options offered are only the columns which contain strings.
Select the line width for the text labels; this effectively controls how bold the labels appear.
This option offers the choice of font for the labels.
Adjust the size of the text labels.
This option enables the user to select a color for the labels, which can of course be different to the color of the markers themselves.
The labels can be drawn at any rotation, so this option allows the setting of that angle in integer degrees.
Labels can be offset vertically and horizontally from the markers. Careful use of these options and the label angle can be used to avoid most conflicts between labels and markers.
This roll-up provides options for controlling the appearance of the markers used to mark the positions of the sources.
This option is a poor but functional way to choose a marker for your sources from the catalog.
This option controls the size of the markers.
Markers can be drawn in any of the available colors selected from this menu.
In this roll-up, some general properties of the catalog overlay can be set.
Long > 0 && Long < 1Two nice features of TaQL are:
Name == pattern('NGC*')
Name == regex('^NGC.+')
Raster measurement set Viewerdisplaydatas have some inputs similar to those for raster image display, with some additional interface for selecting and editing (flagging) the MS data.
This roll-up provides choice boxes for Visibility Type (Observed, Corrected, Model, Residual) and Component (Amplitude, Phase, Real, or Imaginary).
Changes to Visibility Type or Component (changing from Phase to Amplitude, for example) require the data to be retrieved again from the disk into memory, which can be a lengthy process. When a large MS is first selected for viewing, the user must trigger this retrieval manually by pressing the 'Apply' button, after selecting the data to be viewed (Field IDs and Spectral Windows, below).
Changing visibility type between 'Observed' and 'Corrected' can also be used to assure that data and flags are reloaded from disk. You should do this if you're using another flagging tool simultaneously (such as autoflag or msplot), so that the viewer sees the other tool's new edits and doesn't overwrite them with obsolete flags. The 'Apply' button alone won't reload unless something within the viewer itself requires it; in the future, a button will be provided to reload flags from the disk unconditionally.
You can also choose to view the difference from a running mean or the local RMS deviation of either Phase or Amplitude (this will not require a disk reload). There is a slider for choosing the nominal number of time slots in the 'local neighborhood' for these displays.
(Note: Insufficient Data is shown in the tracking area during these displays when there is no other unflagged data in the local neighborhood to compare to the point in question. The moving time windows will not extend across changes in either field ID or scan number, so you may see this message if your scan numbers change with every time stamp. An option will be added soon to ignore scan boundaries).
You can retrieve and edit a selected portion of the MS data by entering the desired Spectral Window and Field ID numbers into these boxes. Especially with large MSs, it makes sense to edit only one or two fields at a time, and to select spectral windows which all have the same number of channels. Doing this will also greatly reduce data retrieval times and memory requirements.
You can separate the ID numbers with spaces or commas; you do not need to enter enclosing brackets. Changes to either entry box will normally cause the selected MS data to be reloaded immediately from disk. If you wish, you can turn off 'autoapply', in order to change both spectral window and field selections, without reloading data after each change. In that case, press 'Apply' after entering all your selections.
If you select, say, spectral windows 7, 8, 23, and 24, the animator, slice position sliders, and axis labelling will show these as 1, 2, 3, and 4 (the 'slice positions' or 'pixel coordinates' of the chosen spectral windows). Looking at the position tracking display is the best way to avoid confusion in such cases. It will show something like: Sp Win 23 (s 3) when you are viewing spectral window 23, the third selected spectral window.
Changes to MS selections will not be allowed until you have saved (or discarded) any previous edits you have made (see Flagging Options - Save Edits, below).
Initially, all fields and spectral windows are selected. To revert to this 'unselected' state, choose 'Original' under the wrench icons next to the entry boxes.
This rollup is very similar to that for images: it allows the user to choose which axes (from Time, Baseline, Polarization, Channel, and Spectral Window) are are on the display and the animator. There are also sliders here for choosing positions on the remaining axes.
Changing the choice of axis on one control will automatically swap axes, maintaining different axes on each control. Changing axes or slider/animator positions does not normally require pressing 'Apply'-the new slice is shown immediately. However, the display may be partially or completely grey in areas where the required data is not currently in memory, either because no data has been loaded yet, or because not all the selected data will fit into the allowed memory (see Max. Visibility Memory, below). When the cursor is over such an area, the following message shows in the position tracking area:
press 'Apply' on Adjust panel to load data
Pressing 'Apply' will reload the memory buffer so that it includes the slice you are trying to view.
The message No Data has a different meaning; in that case, there simply is no data in the selected MS at the indicated position.
For large measurement sets, loading visibility data into memory is the most time-consuming step. At present it is not possible to show the usual progress meter window, but similar feedback is provided in the console window. Again, careful selection of the data to be viewed can greatly speed up retrieval.
These options allow you to edit (flag or unflag) MS data. The crosshair and rectangle region mouse controls are used on the display to pick the data region to edit; the options below determine how the edits will be applied.
You have the option to display flagged regions in the background color (as in msplot or TVFLG) or to highlight them with color. In the former case, flagged regions look just like regions of no data. With the color option, flags are shown in shades of blue: darker blue for flags already saved to disk, lighter blue for new flags not yet saved; regions with no data will be shown in black.
This setting determines whether selected regions will be flagged or unflagged. In contrast to msplot, this does not affect previous edits; it only determines the effect which later edits will have. Both flagging and unflagging edits can be accumulated and then saved in one pass through the MS.
These flagging extent checkboxes have a similar operation to those in msplot. They allow you to extend your edit over any of the five data axes. For example, to flag all the data in a given time range, you would check all the axes except Time, and then select the desired time range with the region mouse control. Such edits will extend along the corresponding axes over the entire selected MS (whether loaded into memory or not) and optionally over unselected portions of the MS as well (Use Entire MS, below). Use care in selecting edit extents to assure that you're editing all the data you wish to edit.
This control can be used to extend subsequent edits to all baselines which include the desired antenna[s]. For example, if you set this item to 'Yes' and then click the crosshair on a visibility point with baseline 3-19, the edit would extend over baselines 1-3, 2-3, 3-3, 3-4, 3-5, 3-6, ... 3-<nAntennas>. Note that the second antenna of the selection (19) is irrelevant here-you can click anywhere on the display where the first antenna number is 3, to select all baselines which include antenna 3.
This item controls the edit extent only along the baseline axis. If you wish to flag all the data for a given antenna, you must still check the boxes to flag all Times, Channels, Polarizations and Spectral Windows. There would be no point, however, in activating both this item and the 'Flag All Baselines' checkbox. You can flag an antenna in a limited range of times, etc., by using the appropriate checkboxes and selecting a rectangular region of visibilities with the mouse.
The 'Undo' buttons do the expected thing: completely undo the effect of the last edit (or all unsaved edits). Please note, however, that only unsaved edits can be undone. In contrast to msplot, there is no ability to revert to the flagging state at the start of the session, once flags have been saved to disk.
"Yes" means that saving the edits will flag/unflag over the entire MS, including fields (and possibly spectral windows) which are not currently selected for viewing. Specifically, data within time range[s] you swept out with the mouse (even for unselected fields) will be edited.
In addition, if "Flag/Unflag All..." boxes were checked, such edits will extend throughout the MS. Note that only unselected times (fields) can be edited without checking extent boxes for the edits as well. Unselected spectral windows, e.g., will not be edited unless the edit also has "Flag/Unflag All Spectral Windows" checked.
Warning: Beware of checking "All Spectral Windows" unless you have also checked "All Channels" or turned "Entire MS" off; channel edits appropriate to the selected spectral windows may not be appropriate to unselected ones. Set "Use Entire MS" to"No" if your edits need to apply only to the portion of the MS you have selected for viewing. Edits can often be saved significantly faster this way as well.
Also note that checkboxes apply to individual edits, and must be checked before making the edit with the mouse. "Use Entire MS", on the other hand, applies to all the edits saved at one time, and must be set as desired before pressing "Save Edits".
The measurement set Viewerdisplaydata works like a text editor in that you see all of your edits immediately, but nothing is committed to disk until you press 'Save Edits'. Feel free to experiment with all the other controls; nothing but 'Save Edits' will alter your MS on disk. As mentioned previously, however, there is no way to undo your edits once they are saved, except by manually entering the reverse edits.
Also, you must save (or discard) your edits before changing the MS selections. If edits are pending, the selection change will not be allowed, and a warning will appear on the console.
If you close the tool, unsaved edits are simply discarded, without prior warning. It's important, therefore, to remember to save them yourself. You can distinguish unsaved flags (when using the 'Flags In Color' option), because they are in a lighter shade of blue.
The program must make a pass through the MS on disk to save the edits. This can take a little time; progress is shown in the console window.
These four rollups contain entries similar to those for image Viewerdisplaydatas. Some of those entries were unnecessary and were omitted for simplicity here; others will be added in the future.
Together with the brightness/contrast and colormap adjustment mouse controls on the Viewerdisplaypanel, the following Basic settings are especially important for adjusting the color display of your data:
At present, these are only sliders, without the histogram capabilities of the image Viewerdisplaydatas. Lowering the data maximum will help brighten weaker data values.
This has exactly the same usage as for image Viewerdisplaydatas. Again, lowering this value often helps make weaker data visible. If you want to view several fields with very different amplitudes simultaneously, this is probably the first adjustment you should make.
Greyscale or Hot Metal colormaps are generally good choices for MS data.
Adding a Color Wedge to the right of your display helps to show the effect of your other color scale adjustments. Its displayed scale and units are not always up-to-date at present (a known problem, to be fixed soon). In the meantime, moving the slider for Data minimum or maximum will cause the correct scale to be displayed.
These settings can help optimize your memory usage, especially for large MSs, if you feel comfortable tweaking such things. A rule of thumb is that they can be increased until response becomes sluggish, when they should be backed down again.
You can run the unix 'top' program and hit 'M' in it (to sort by memory usage) in order to examine the effects of these settings. Look at the amount of RSS (main memory) and SWAP used by the X server and 'glishtk' processes. If that sounds familiar and easy, then fiddling with these settings is for you. Otherwise, the default settings should provide reasonable performance in most cases.
As with the Skycatalog, the value of this option specifies the maximum number of different views of the data to save so that they can be redrawn quickly. If you run an animation or scroll around zoomed data, you will notice that the data displays noticably faster the second time through because of this feature. Often, setting this value to the number of animation frames is ideal Note, however, that on multi-panel displays, each panel counts as one cached image.
Large images naturally take more room than small ones. The memory used for these images will show up in the X server process. If you need more Visibility Memory (below) for a really large ms, it is usually better to forgo caching a large number of views.
This option specifies how many megabytes of memory may be used to store visibility data from the measurement set internally. Even if you do not adjust this entry, it is useful to look at it to see how many megabytes are required to store your entire (selected) MS in memory. If the slider setting is above this, the whole selected MS will fit into the memory buffer. Otherwise, some data planes will be 'greyed out', and the selected data will have to be viewed one buffer at a time, which is somewhat less convenient. The largest process called 'glishtk' contains this buffer memory; it actually contains the entire display library, but the memory buffer can dominate its size.
