Manipulating VOTables with TOPCAT and STILTS

Tom McGlynn

What are TOPCAT and STILTS?

• STILTS is a powerful library that enables users to filter and convert tables in VOTable and other popular formats.

• TOPCAT is a user interface built on top of STILTS with extensive GUI and graphics capabilities.

• All written by Mark Taylor (Bristol University/UK) originally as part of the Starlink project.

• This demo uses TOPCAT but the underlying functionality is available through the STILTS library (in Java).

• There are some other standalone commands built on STILTS (e.g., votcopy).

• There is a TOPCAT chapter in the NVO book.

Starting TOPCAT

• In the standard distribution as command ‘topcat’

• Note capabilities to download data from various VO and other data sources.

• Remember to run setup first!• Files used in this presentation:

Download these (Twiki doesn’t let TOPCAT read them directly)– http://nvo-twiki.stsci.edu/twiki/pub/Main/NVOSS2008Sched/spocs.csv– http://nvo-twiki.stsci.edu/twiki/pub/Main/NVOSS2008Sched/spocs.xml– http://nvo-twiki.stsci.edu/twiki/pub/Main/NVOSS2008Sched/exostars.xmlThis URL can be used directly– http://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=messier

Starting and loading a URL

Table loaded successfully

Getting to and from VOTables

• Converting to VOTables from CSVLoad spocs.csv (available on Twiki)Save as spocs.xml (VOTable)

Can covert into many formats.• Converting VOTables to CSV

Load http://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=messier

Save as CSV

Portal tools may work better in handling data in non-standard formats.

Convert to a CSV file

After loading CSV convert to VOTable

The table browser

Filtering data using TOPCAT

• Show SPOCS table (view/tabledata)• Create a subset (view/row subsets/+)

– Enter name=Sunlike– Enter criterion Teff>5720 && Teff<5820 &&

log_g>4.34 && log_g<4.54 && M_H>-0.1 && M_H <0.1

– Should create subset with ~30 rows.– Show with Views/Table data/Apply Subset/Sunlike

• We can use column names or $number.• A sample can be saved in any of the supported

formats.

Creating a subset

Histograms

• Click on histogram– Note which subsets are showing and click

on all– Change column to VMAG– Note both all and sunlike data.

Histograms

Plots

• X/Y display– Ensure that full sample is shown.– Change parameters to Teff/Age– Zoom around sun location– Create new sample from plot (third box

from right)– Note region selection tool (fourth from right)

X-Y plots

Creating a subset graphically

3-D Graphics/Synthetic columns

• 3-d displays (change third axis to something interesting in box)

• Creating new columns: column metadata/+– Name = AppMag– Expr = Vmag – 5*log10(Dist/10) [note striping

error]– Note function browser– New columns can be used anywhere and

show up on output

3-D plots

Creating a new column

Correlations using TOPCAT

• Load– SPOCS table– EXOStars table

• Click on double match• Cross-correlate by position:

– Find all the SPOCS stars that have exoplanets

Cross-correlations

Viewing the correlation

Saving the correlated data.

Many more capabilities

• Direct access to VO enabled services• Density plots• Column data conversions• Hundreds of functions usable in creating

columns• PLASTIC/SAMP communication with other tasks• Joining tables• Stacked plots or spherical plots• Table statistics• …