Data Discovery Tool: Plots

Plots can be made from Tables, and plots are made automatically in the Data Discovery Tool -- it attempts to make an SED for you (from either NED

or VizieR

). Plotting is covered in this section. The Tables section discusses tables more generally. The Visualization section covers intearcting with images.

Contents of page/chapter:
+Default Plot
+Plot: A First Look
+What is it plotting?
+Plot Linking
+Plot Navigation
+Changing What is Plotted
+Restricting What is Plotted
+Overplotting

Default Plot

By default, after doing a search, a plot appears in the upper right of your browser window.

To obtain a full-screen view of the plot, click on the expand icon in the upper right of the window pane when your mouse is in the window: . To return to the prior view, click the "Close" arrow in the upper left.

The plotting tool in the Data Discovery tool, by default, has the spectral energy distribution (SED) for your search target, pulled either from NED (works best for extragalactic objects) or VizieR .

Plot format: a first look

This is the SED that the Data Discovery tool shows for Arp 220, with the data being retrieved from NED.

Letting your mouse hover over a point tells you the values of the point under your cursor:. Clicking (in an unbinned plot) highlights that point, and it stays highlighted, though you must keep your mouse on the point in order to see the information about how many points it represents.

This is the SED that the Data Discovery tool shows for HD 878, with the data being retrieved from Vizier.

What is it Plotting?

The tool is plotting its best guess as to what the SED is of the object. The y-axis is nuF_nu and the x-axis is wavelength in microns.

NED

If it uses NED to translate the name of the object to RA/Dec, then it will use NED data to get an SED. Very common names are resolved via NED but may not have an SED in NED. Try "M101" to get an SED; try "M16" to get the coordinates from NED but find no SED.

The units from the points are what are supplied by NED. (Note that the carats are used in an on/off sense, e.g., erg s^-1^ cm^-2^ means ergs per second per centimeter squared, where the first carat means "superscript" and the second carat means "back to normal".) No additional translation has been done here, aside from multiplying to get nuF_nu.

The points that NED reports can come in a variety of units, but the data are filtered down to only include those in units of Jy before multiplying and plotting.

VizieR

If it uses SIMBAD to translate the name of the object to RA/Dec, then it will use VizieR to get an SED. Try the name of a star (like HD 878) to get an SED.

The VizieR photometry tool allows for easy visualization of photometry points extracted around a sky position from photometry-enabled catalogues in VizieR. Even when an object name is used as a target, what is returned is just a list of photometry points found within some search radius, and should not be mistaken for an actual SED for the target object -- there is no guarantee that all photometry points correspond to the target, especially for extended sources or stars in a cluster in close (projected) proximity.

Note that, for VizieR searches, an additional circle appears on the image on the left; this is the search radius used to retrieve the points from VizieR that are shown here.

Plot Linking: Plots are linked to catalog and image(s)

If you move your mouse over any of the points in the plot, you will get a pop-up telling you the values corresponding to the point under your cursor. If you click on any of the points, the object(s) corresponding to that point will be highlighted in the SED table -- you may need to click on the SED tab at the bottom to bring it to the foreground. This works the other way too - click on a row in the SED tab, and the object will be highlighted in the plot or the catalog or the image.

The actual data table is a a table like any other here, so you can search and sort that table too.

Plot Navigation

The top right of the plot window has a row of icons:

which we now describe.

Plot mode

This trio of icons controls the plot interaction 'mode'. By default, you are in 'selection' mode, as seen here -- the last icon is darker, like a pushed-in button. To activate the other modes, click on the other icons, and they become darker or "pushed in."

Zoom mode: When this mode is active, when you click and drag in the plot, the plot is zoomed to the region you have selected. Even when this mode isn't active, you can also zoom using your scroll feature on your mouse. To return to the original view, click on .
Pan mode: When this mode is active, when you click and drag in the plot, it moves around in response to where you drag. To return to the original view, click on .
Select mode: When this mode is active, when you click and drag in the plot, you are given additional options at the top of the plot : The checkmark means "select" and the funnel means "filter." The difference is that filtering (temporarily) limits what is shown in the plot, catalog, and image (see general information on filters), and selecting just highlights the points enclosed within your selection. To cancel either one, click on cancel filters or cancel selection .

Re-scale plot

Return to the view that optimizes the range of x and y to show the currently displayed points.

⚠ Tips and Troubleshooting: Did you accidently zoom in the plot with your magic mouse or touchpad? Click on this icon to reset the plot.

Save plot

Save the plot. It will save as a png file, wherever your browser is configured to save files. The saved png is the same size as it is on your screen. If you want a big version, make the desired plot big on your screen (expand the view to take up as much space as possible) before saving the png.

Undo

Restore everything to the defaults. If you've played a lot with the plot, you may want to undo everything you've done. Click this icon to restore everything back to the defaults.

Filter from plot

Pull up interactive filters. This button brings up filters for the displayed catalog in an interface like all the other tables here, except you don't see the values in the catalog themselves; you can enter filters here in the same way you can everywhere else in this tool (see general information on filters).

Configure plot

Click on this icon to change what is plotted (much more on this below).

Expand plot

Click on this icon to make the plot take up the whole browser window. To return to the prior view, click the "Close" arrow in the upper left.

Help

This icon may not appear, but if it does, it is a context-sensitive help marker, which should bring you to this online help.

Changing what is plotted

To change what is plotted, click on the gears icon in the upper right of the plot window pane:

. Configuration options then appear; the options are a little different than other plots in tools like this:

This section describes how to change what is plotted, i.e., the "Modify Trace" option at the top of the pop-up. Overplotting is covered in more detail below.

You can specify what should be plotted on each axis. The magnifying glass is a link that brings up a table that lists all of the available columns in the catalog. Alternatively, you can just start typing, and viable options appear below the box. Whatever you put in the box must match the column name as shown in the catalog exactly.

Click on the black triangle to reveal additional options.

The default plot is an SED from either NED or VizieR (see above) and is manipulating the columns to make the SED in reasonable units. You can change what column is plotted, and whether or not errors are shown.

By default, the boundaries of the plot are set to encompass the full data range. Here you can change the boundaries to specific numbers. (This can also be set via filtering from the plot; see below.)

You can enter simple mathematical relations in these boxes too, such as (for a WISE catalog) "w1mpro-w4mpro" to put [W1]-[W4] on one axis. Supported operators:

+,-,*,/
abs(x), acos(x), asin(x), atan(x), atan2(x), ceil(x), cos(x), exp(x), floor(x), lg(x), ln(x), log10(x), log(x), power(x,y), round(x), sin(x), sqrt(x), tan(x)
degree(x) and radians(x) are also supported -- these are the same functions as in ADQL and convert radians to degrees or degrees to radians. For small astrometric offsets, you could make a scatterplot of dec2-dec1 vs. (ra2-ra1)*cos(radians(dec1)) instead of typing cos(dec1*pi()/180). (NB: pi() is also a supported function you can use, instead of typing 3.14159.)
Non-alphanumeric column names (e.g., those with - or + or similar characters) should be quoted in expressions.

Under "Trace Style," you can control whether the points are shown as individual points, connected points, or just lines connecting the points.

Under Trace Options, you have many choices.

Choose the symbol type: circle (default), open circle, square, open square, diamond, open diamond, cross, x, upward-pointing triangle, hexagon, or star.
Choose the color. By default, the point color is a mid-range blue that is darker where more points. This is specified by the rgba vector shown in the example here (31, 119, 180, 50) where the last number is in units of fraction of 1, so 0.5=50% in this example. Click on the magnifying glass to bring up a color picker window:

From here, you can click on your desired color in the top colorful box. Immediately below that box, you can change the color and saturation of the top box so that you can select from a different range of colors. Below that, you can enter numerical hex codes or RGBA values (where the value for RGB is between 0 and 255, and A is in units of percent, e.g., 50 = 50%). Finally, you can also select from a pre-defined set of 15 colors by clicking on any of the small boxes. Note that the numerical codes update as you select different colors. Click "OK" to implement your color choice, or click 'x' in the upper right to close the window without changing the color.
⚠ Tips and Troubleshooting: Don't like the transparency feature of the points that makes them darker when there are more points? Set the last value of the vector (A) to 1. Don't like the blue? Pick a diferent color entirely. Want the faintest point to be brighter than it is by default? Set the last element of the color vector ("A") to be 0.7 or 0.8.
Choose the color map. By default, all of the points are the same color, but darker where there are more points. You can change this such that the color scale of the points is tied to a column value, such as w1snr (WISE-1 signal-to-noise ratio) in a WISE catalog. If you select this option, you can also change the color scale to any of many different options (see the drop-down). Simple mathematical relations (as above) are also permitted in this box.
Choose the size map. By default, all of the points are the same size. You can change this such that the color scale of the points is tied to a column value, such as w1snr (WISE-1 signal-to-noise ratio) in a WISE catalog. Simple mathematical relations (as above) are also permitted in this box.

Under "Chart Options", you can specify:

title of the plot;
labels on the x and y-axis;
whether or not there is a grid;
whether or not the axis is reversed (as for ra in the examples above);
whether the x-axis is on the top or bottom and the y-axis is on the left or right;
whether or not the axis is logarithmic;
the maximum and minimum values of the plot range;
the aspect ratio of the plot (e.g., square or rectangular).

By default, the boundaries of the plot are set to encompass the full data range. Here you can change the boundaries to specific numbers. (This can also be set via filtering from the plot; see below.)

⚠ Tips and troubleshooting:

VizieR searches by position to find all counterparts. As such, you may want to change the plot to be RA/Dec and filter down so that you select different counterparts. Then, you'll want to return to the SED view of your now filtered points. The values to copy back into the plot parameters box are:
- x: 2.998*power(10,14)/("_sed_freq"*power(10,9))
- no x errors by default
- y: ("_sed_flux")*("_sed_freq"*power(10,9))
- y error, symmetric: ("_sed_eflux")*("_sed_freq"*power(10,9))
NED SEDs are curated, so outliers are less likely to be a problem. BUT if you need them, the values to copy back into the plot parameters box are:
- x: 2.998*power(10,14)/("Frequency")
- no x errors by default
- y: ("Flux Density")*("Frequency")
- y error, symmetric: ("Upper limit of uncertainty")*("Frequency")

Restricting What is Plotted

You can also restrict what data are plotted in any of several different ways.

You can filter the table itself (discussed in another section).

You can set axis limits on the plot itself from the plot options pop-up (discussed above).

However, and perhaps more powerfully, you can set limits from the plot itself using a rubber band zoom. Click on the select icon in the plot () Click and drag in a sub-region of the plot. New icons appear: If you click on the funnel icon, only those data points that pass the filter are shown in the plot, in the table, and/or overlaid on the image(s). (This is the behavior of 'filter', as opposed to 'select'; the former restricts what is shown, the latter just highlights the points.) For more on filters, see the filtering discussion in the tables section.

If you move your mouse over any of the points, you will get a pop-up telling you the values corresponding to the point under your cursor. If you click on any of the points, the object(s) corresponding to that point will be highlighted in SED table. This works the other way too - click on a row in the SED table, and the object will be highlighted in the plot.

You can also zoom with your mouse on the plot -- do whatever you would do with your mouse to scroll but with your mouse over the plot.

Overplotting

At the top of the pop-up that you get when you click on the gears, you have two radio buttons:

They are "Overplot New Trace" and "Modify Trace." Modifying traces (plots) has been covered above; in this section, we will cover overplotting. This is sometimes called "multi-trace," meaning that more than one thing is plotted.

When you select "Overplot New Trace," you get a new interface that is very similar to the original interface where you selected what to plot:

As before, you need to :

select a plot type (scatter, heatmap, histogram);
tell it what column(s) (and and manipulations thereof) you want for x, y, and associated errors;
select the trace style (points, connected points, lines);
set any additional trace options;
set any additional chart options.

The best way to explain how to use this feature is probably via an example. I have a plot of [W1] vs. [W1-W4]. Now I am going to add on top of it a plot of [W2] vs. [W1-W4]. Click on the gears to bring up the pop-up. Select "Overplot New Trace." Enter "w1mpro-w4mpro" for x and "w2mpro" for y. Expand "Chart Options." Note that it has preserved the overall chart title from before, but has erased the X and Y labels (and lost the reversal of the y axis) because the overplot could literally be anything, and need not be the same columns or even the same units as what is already plotted. Type them in again. Here is the configuration window right before clicking "ok", and the resultant plot.

After you add the overplot, if you click on the gears again, note that the choices at the top of the window have changed. You can add another overplotted trace, modify a trace, or remove the active trace. Each trace that you add is a new 'layer' on the plot. The drop-down menu near the top of the window controls which trace is 'active' for setting the x, y, errors, trace style, name, symbol, color, etc. there is now a drop-down menu at the top of the plot: There is a legend on the plot specifying which color corresponds to which trace. In this example, the plot above has appeared using a blue and green color scheme, which may be too hard to differentiate. To change the new points' color, click on the gears, ensure "Modify Trace" is selected, select "trace 1" (as opposed to "trace 0", the first one you loaded), go down and expand the "Trace Options" and pick a different color. You can also change the legend name from "Trace 1" to, in this case, "[W2]". Click "apply" to apply the changes to the plot. Note that once you change the trace name, the relevant drop-down menus in the pop-up window and the legends on the plot update accordingly.

Note that the pop-up spawned by clicking the gears now has an additional option at the top: "Add New Chart", "Overplot New Trace", "Modify Trace", and "Remove Active Trace." From here, you can modify a trace you have already plotted (as described above), overplot another trace (also as described above), or remove the selected trace:

⚠ Tips and Troubleshooting

Right now, the overplotting only works from the same catalog -- that is, you cannot plot [W1] vs. [W1]-[W4] from one catalog and overplot [W1] vs. [W1]-[W4] from another catalog. (We enthusiastically await this capability too.)
You can easily get yourself into a physically nonsensical situation, say, by overplotting a histogram onto a scatter plot. If you find yourself in a hopeless mess, click on the "undo" icon to reset everything and try again.
When you have more than one thing (trace) plotted, double click on the legend to bring that trace to the foreground and temporarily hide the other traces.