ESO Archive Frequently Asked Questions
How do I export search results?
In order to export search results from large datasets, users can follow one of the two options below:
There is an export option into three different ASCII data formats, with values separated by tabs (\t), commas, or pipe simbols (|). This can be combined with the "Return a maximum of n rows" setting, in order to retrieve a really large number of rows.
This can be accomplished by performing the following actions on the ESO Archive main query form:
- Check the Use tabular output radio button
- Check the Exports results to file checkbox, selecting additionally whether a Tab-separated-values, Comma-separated-values, or Pipe-separated-values is to be generated.
- Optionally, set the "Return a maximum of" to the number of expected rows (ie, 20000).
- When more than 10000 rows are expected, it is advised to uncheck the "Number of Frames / Instrument" and "Cumulative Exptime / Filter" options, as they might cause a timeout precluding the form from completion, and might end up not showing the export link.
After the query is completed (it might take as long as 15 minutes for a 20000 results query), the download link provided will be available for XXX time [please check] for reuse.
Command-line downloads, and VOTables
For users who prefer to download query results using command-line tools, they will have to build a query URL that can be used with downloading tools such as curl or wget.
Building a query URL
Query parameters have to be identified on the ESO Main archive query form (where they are identified as INPUT HTML tags). A selection of them follows:
- max_rows_returned: controls the maximum numbers of rows to be returned; used by the "Return a maximum of" option.
- Parameters governing extra fields to be returned:
- tab_object: target information
- tab_dp_cat: category information
- tab_target_coord: actual target coordinates
- tab_night: extra night information
- tab_obs_name: actual name of the observing block
- tab_origfile: adds the orinal file name as provided to the archive system (i.e., as saved in the PI pack)
- Common query parameters:
- target: target name; it must be used jointly with resolver, so that the target is converted to coordinates.
- resolver: one of simbad or ned; indicates which name resolver service will be used to convert the target name into coordinates.
- ra: right ascension; only if no target name is provided; can be a blank separated sexagesimal value, or a decimal one. See deg_or_hour.
- dec: declination; only if no target name is provided; can be a blank separated sexagesimal value, or a decimal one.
- deg_or_hour: can be one of degrees, or hours, and affects only the interpretation of the ra field when given in sexagesimal format.
- format: affects how coordinates are going to be shown in the results. SexaHour means sexagesimal format, with RA in HMS format; DecimHour means decimal format, with RA in hours, and DecimDeg means decimal format, with both RA and Dec in degrees. Requires tab_target_coord set to true.
- Format parameters:
- votable_out_mode: when set to true, returns an on-the-fly generated VOTable. The VOTable data format is a metadata-rich output format, that can be manipulated by GUI tools such as or command-line tools such as
Which if used would cause a browser, or command line tool, to download up to 2000 rows (max_rows_returned=2000) of calibration data (category=CALIB), corresponding to observations around an object known as Vega (target=vega), as resolved by Simbad (resolver=simbad) in VOTable format (votable_out_mod=true), with target coordinates written in decimal degrees (tab_target_coord=true&format=DecimDeg).
In order to download such VOTable, we would have to issue a suitable curl or wget command (see examples below), or used in a web browser, or users' favourite download manager.
In order to manipulate the VOTable from the command line, a package such as STILTS can be used. A few examples follow using the URL above, but more information can be found on the .
The output.votable.xml file can later be transformed into ASCII, CSV, TSV, or even a FITS binary table using the
As the STILTS toolset allows for the concept of "remote files", the URL can be used as input parameter:
By using the tpipe option, some additional filtering can be performed:
The fixcolnames command substitutes characters problematic for STILTS in column names by underscores (in the case of the ESO archive, the dot between data_products and dp_cat, for instance.