IRSA Viewer: Plots

Contents of page/chapter:
+Default Plot
+Plot Format: A First Look
+Plot Navigation
+Plot Linking
+Changing What is Plotted
+Plotting Manipulated Columns
+Restricting What is Plotted
+Overplotting
+Adding Plots
+Pinning Plots
+Combining Plots
+Examples

Default Plot

To obtain a full-screen view of your 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, by default, starts with RA and Dec plotted if it can find RA and Dec in the corresponding table. Note that it does so following astronomical convention -- RA increases to the left. If the catalog does not have RA and Dec, it plots the first two numerical columns it finds.

Plot Format: a First Look

The difference between them is that, for larger catalogs (left), the plot is binned, or 'decimated' -- the shades of grey correspond to how many points are encompassed in each 'cell', with the density scale given on the right hand side of the plot. In the context of this tool, this is called a heatmap. For smaller catalogs (right), each individual point is shown as a blue dot. In the context of this tool, this is called a scatter plot. Note that even when individual points are shown, where the points overlap, the color is darker.

In either case, letting your mouse hover over a point tells you the values of the point under your cursor, and (if binned) how many points are represented:
for binned plots, and
for just one point.
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 it.

The reason the tool makes a heatmap for large catalogs is to more fairly represent the point density -- and to make the plotting faster. In these cases, though, it will not give you the option to overplot errors (see below). If you have a heatmap and want a scatter plot, you need to filter or otherwise restrict the catalog to have fewer points (see below). You can change the bin size and shading via the plot options pop-up (more on this below).

Plot Navigation

Add new plot

You may or may not have this icon. Clicking on this icon adds a new plot. This has a separate section below.

Pin plot

This icon may not always appear. Clicking on this icon pins the plot. This has a separate section below.

Show table

This icon does not always appear. Clicking on this icon pulls to the foreground the table that generated the plot that is currently in the foreground. This is related to pinning, which has a separate section below.

Combine chart

This icon does not always appear. Clicking on this icon attempts to combine plots; it has a separate section below.

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.

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

Changing What is Plotted

This is the configuration window for a binned (a.k.a. decimated, heatmap, and/or greyscale) plot. By default, the "chart options" may be hidden; to reveal them, click on the name "Chart Options" or the disclosure arrow on the right. To hide them again, click on the disclosure arrow on the right.

The configuration window for a plot that shows individual points, once fully extended, is much longer (and scrollable), and so is shown here in two parts. Both the "Trace Options" and "Chart Options" may be hidden by default; to reveal them, click on the name or the disclosure arrow on the right. To hide them again, click on the disclosure arrow on the right.

Options found in both kinds of plots

In either case, 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.

In both of the examples above, RA is plotted on the x-axis. It has pulled the column name for the label; in this table, the column is "ra" rather than "RA", and it is case-sensitive. It has copied over the units ("deg") from the catalog, and plotted the x-axis increasing to the left as per astronomical convention. You can change what column is plotted, and whether or not errors are shown. Under "Chart Options", you can specify:

• title of the plot;
• labels on the x and y-axis;
• whether or not there is a grid shown;
• 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.)

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.

Click "Apply" to apply, and "Close" to return to the plot without making changes. (For the latter, you can also click the 'x' in the upper right.)

Options found only in binned plots

(Plots are binned if there are > 5,000 points in the catalog.) From the pop-up, you can control the color table that is used (greyscale is the default; there are many other choices in the drop-down menu), as well as the number of bins in the x and y directions. The default value for the number of bins is 100 in both directions.

Options found only in plots showing individual points

You can add errors. Toggle the error switch, and then additional choices appear. From there, you can select symmetric or asymmetric errors, and then you can specify an error as either an existing column in the catalog, or calculated from a column in the catalog.

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.

Example: Load either a smaller WISE catalog, or the same large WISE catalog, but filter it down such that w1snr, w2snr, and w3snr are all greater than 10, which limits the number of points to be <5,000. Plot w1snr vs. w1mpro. It shows the points individually. Change the labels. Change the point color map to scale with w2mpro (WISE-2 profile fitted magnitude). Change the point size map to scale with w4snr (WISE-4 signal-to-noise). Obtain this plot:

Plotting Manipulated Columns

For example, if you have loaded a WISE catalog, you can plot [W1]-[W2] vs. [W3]-[W4]. In terms of the names of the columns in the database, this is w1mpro-w2mpro vs. w3mpro-w4mpro.

If you have few enough points that the plot is not binned, you can add errors that you calculate. Here, the expression for the x-axis errors is sqrt(power(w1sigmpro,2)+power(w2sigmpro,2)) and for the y-axis errors, it is sqrt(power(w3sigmpro,2)+power(w4sigmpro,2)) -- that is, the errors for the individual photometric points added in quadrature.

Restricting What is Plotted (from the plot)

You can filter the catalog from 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 Then, 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.

Example: Obtain a WISE catalog of a star-forming region, say IC1396. Filter down the catalog to only have detections at all four WISE bands. (Limits have undefined errors, so ask the catalog to filter down such that w1sigmpro>0, w2sigmpro>0, w3sigmpro>0, and w4sigmpro>0). Plot w1mpro-w4mpro on the x-axis, and w1mpro on the y-axis. Reverse the y-axis to put bright objects at the top. Click and drag in the plot to select the bright and red objects, and filter them down to get a subset of bright and red sources. For clarity, the screenshot here has the sources selected, not filtered.

Overplotting

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. We have a plot of [W1] vs. [W1-W4] from above. Now 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.

Adding Plots

Scatter plots allow you to choose points, connected points, or lines; you can add errors to each point. There is a maximum of 5,000 points for scatter plots.

Heatmap plots are binned scatter plots; you can choose what color scale and how many bins to use.

Histogram plots allow you to choose how many bins or the bin width. Note that, if you provide a minimum number, the binning starts at the minimum value you provide, and may exceed the maximum you entered in order to fit in a whole bin.

You can change what is plotted after plotting by clicking on the gears, as described above.

You can have many plots up at the same time.

You can view multiple plots all at once or one at a time by clicking on the corresponding icons above the plots (just as when you have multiple images loaded). The single box means "one at a time", the set of four boxes means "all the plots at once". If you are viewing one at a time and have more than one plot loaded, you will see the ">" and "<" signs (as in the image here), and you can scroll among the plots by clicking on these arrows (just as when you have multiple images loaded).

⚠ Tips and Troubleshooting

• Note that many plots of a large catalog may make your browser run slowly.
• The tool will refuse to make a scatter plot for catalogs with >5,000 points.
• To remove a plot, click on the 'x' in the upper right corner of the plot.

Pinning Plots

When you make a plot that you want to retain, click on the "pin chart" icon and it will make a copy of that chart and keep it in your plot area, even as you continue to make more plots and work with more catalogs.

It saves your pinned plot in a different tab than your current plot. To change between them, just click on the corresponding tab. Here, there are three pinned charts, but the current view is the active chart:

⚠ Tips and Troubleshooting

• When you pin a plot, and then filter its parent catalog, the plot updates correspondingly, because it is still linked to its parent catalog.
• When you have multiple catalogs (or tables of any sort) loaded, if you want to bring to the foreground the catalog tab corresponding to a pinned plot, click on "show table" , and it will bring the corresponding catalog to the foreground of your tables pane.
• If you click on a source in the image (or catalog or plot), the same source is highlighted in the catalog (or image or plot).
• To change a pinned plot, click on the plot to bring it to the foreground, then click on the gears in the the corresponding plot area, and change what is plotted as described above.
• You can view the plots one a time or in a grid by clicking on the icon for one-at-a-time (big square) or tiled (4 small squares; if you are viewing them one at a time, you can use the ">" and "<" arrows to scroll through the list):
• There is a maxium of 12 charts that you can pin at one time.
• When many plots are pinned, and you view many plots at once, the margins on the plots will shrink down to make the data more visible. To view the plots with more reasonable margins, view the plots one at a time.
• To remove a pinned plot, click on the blue 'x' in the upper right corner of the plot.
• If you remove a catalog by clicking on the 'x' in the corresponding catalog tab, the pinned plot will be removed as well.

Combining Plots

This option only appears if you have pinned at least two plots, and it will only let you combine plots if it recognizes that you have spectra loaded. These can be spectra you extracted or have loaded in from a file.

Because combining is only possible for spectra at this time, the information on how to combine plots can be found in the chapter on spectra.

Examples of Catalog Plots

For this example, we are trying to find young stars in a star-forming region. We are searching in the WISE AllWISE catalog. Stars without circumstellar dust should be at a variety of W1 brightnesses, but all have [W1]-[W4]~0. Background galaxies should be faint and red. Stars with circumstellar dust (e.g., young stars) should be bright and red. Here, we will make a plot, identify a bright and red object in the plot, and find where it is in the WISE images.

1. Launch the IRSA Viewer tool. Click on "Images" at the top to search on images. For "Select Image Type", choose "View FITS Images", and for "Image Source", select "Search." Enter target as IC1396. Use Simbad's interpretation of the coordinates. Select image size of 1 degree (pick the units first, then enter the number). Select WISE AllWISE Atlas, all four bands. Click 'Search.'
2. Click on "Catalogs" at the top to search on catalogs. Select Project=WISE. Select the AllWISE database, and the AllWISE Source Catalog. Leave the cone search method and target as what it comes set up with as the default - it is set to the target we just used for our search. However, make sure to change the units of the drop-down to "deg" and enter 0.5 degree in the cone radius to match the images. Leave all the defaults in the Table Selection section. Click "Search." You may have to wait a bit for the catalog to be returned, because there are ~17,000 sources. If you choose to put the catalog search in the background, load it when it is ready.
3. By default, the catalog is overplotted on the images in the upper left, plotted as an x-y plot on the upper right, and loaded as a table on the bottom. Note that the plot on the upper right is a greyscale plot, which means that the plot shows a binned "heatmap" where darker colors mean more points. Note too that this decimation means that all ~17,500 sources are NOT overplotted on the images but a representational subset are overplotted. Only the first 100 are shown in the catalog on the bottom, though all are loaded, and you can page through the list, 100 at a time. Note that selecting a source in the image makes its corresponding row in the catalog change color. It doesn't highlight in the plot, because there are too many points in the plot.
4. Filter down the catalog to only have detections. By default, you should have a place to put in filters at the top of each column, but if you don't, go to the the upper right of the catalog pane, and click on the funnel icon to add filters to the top of each column in the catalog. In this AllWISE catalog, limits have null errors. To limit the catalog to just those with detections, in the top of the "w1sigmpro" (WISE-1 profile fittted magnitude error) column, type ">0" (without the quotes). Repeat for w2sigmpro, w3sigmpro, and w4sigmpro. After this process, you should have ~3,000 sources, enough fewer that the plot now has individual blue points (it is no longer a heatmap). Now the individual sources are also all shown on the images.
5. The plot comes up with an RA/Dec plot by default. Click on the gears icon in the upper left of the plot window to change what is plotted.
6. Ensure "Modify Trace" is selected in the pop-up window (by default, it should be selected). Enter in the x box: w1mpro-w4mpro. This is WISE-1 profile-fitted measurement in magnitudes minus WISE-4 profile-fitted measurement in magnitudes,or [W1]-[W4].
7. Enter in the y box: w1mpro. This is the [W1] mag.
8. Click on "Chart Options", and enter "[W1]-[W4] (mag)" for the x-label, and "[W1] (mag)" for the y-label. Click on "reverse" for the y-axis to make the brighter objects appear at the top of the plot. Check "grid" to make the grid appear for both axes.
9. Click "Apply."
10. Obtain this plot (configuration also provided for reference):
    
    
11. Ensure that the select icon is "active" in the plot (). Click and drag from corner given approximately by (2,6) to (7,11).
12. The icons in the upper right change after you do this, and we want to filter on this region. Click on the filter icon. This filters the table and the image overlays as well as the plot.
13. After this filtering, you should have about 100 points left in the catalog. The scatter plot after the filtering looks something like this:
    
    The points are shown as blue circles. Where they overlap, the blue appears darker.
14. We want to find an (astrophysically) bright and red object in the plot, catalog, and images. In order to find it easily in the images, first, zoom in relatively closely to any of the images. Select the lock drop-down in the image toolbar () and select "Align and lock by WCS." Ensure "pan by table row" is selected from the recenter icon ().
15. Now, find the brightest source near [W1]-[W4]~4.5 in the plot. Click on that point. It is highlighted in the overlays on top of the image, the images have jumped to center it, and it is highlighted in the catalog (though you may need to scroll slightly in the catalog to find the highlighted line). (If you have been following closely, it should be J213808.44+572647.6.)
    

Because you can do simple mathematical manipulations when specifying what to plot or use for errors, you can calculate these things on the fly. From the end of the prior example, cancel the filters, and impose new filters on the catalog by requiring w*snr>10 for all four bands. Intitiate a new plot by clicking on the plot's gears icon, and select "Add New Chart."

For the x-axis, ask it to plot w3mpro-w4mpro. Ask it to use symmetric errors and use sqrt(power(w3sigmpro,2) + power(w4sigmpro,2)). For the y-axis, ask it to plot w1mpro, and use w1sigmpro for the errors. Under "Chart Options", add the x label [W3]-[W4] and the y label [W1]. Reverse the y-axis to get bright objects at the top. Under "Trace Options", select red points just to be fancy. Obtain a plot something like this, which shows the calculated error bars for each point. Note that there are errors in both directions, though they are hard to see in the y direction.

Abbreviated Example: Plotting a histogram of [W1]

Picking up from the end of the prior example. Click on the blue 'charts' tab near the top of the window. Select "histogram." Enter w1mpro for the column. If you leave everything else to the defaults, you can obtain a plot like the below. As for xy plots, mousing over a column tells you more information about the contents of the column.

Still More Plots

Here are several more examples of plots made with IRSA tools.

Phase-folded light curve from K2 data:

Plot on the sky of stars where the color of the point is scaled to brightness in WISE-4:

Gaia distance (in kpc, from Bailer-Jones et al. 2018), with asymmetric errors, as a function of Gaia G magnitude, with colors of the point scaled to brightness in WISE-4:

[W1] light curve of Neptune over several years, with colors of the point scaled to heliocentric distance:

Absolute Gaia color-magnitude diagram of candidate members of a star-forming region (note some background giants still in the list), where point size is scaled by WISE-4 brightness: