### 1 Introduction

PONGO is a set of commands for interactively plotting data stored in ordinary text files. It is based around the PGPLOT (SUN/15) graphics package.

Some highlights of PONGO are:

• Data are read from text files using a command (READF) that has:
• the ability to read files which contain character strings as well as numeric values;
• support for comment lines and column headings as an aid to remembering what the file contains;
• variable column delimiters, allowing LATEX and TEX format tables to be read;
• selective reading of the data;
• the ability to read in positions of Right Ascension and Declination in the format
HH:MM:SS.SSS   +DD:MM:SS.SSS
• Plots of astronomical positional data can be made in one of several geometries (TAN, SIN, ARC, GLS, AITOFF, MERCATOR and STG).
• Complicated mathematical manipulations can be performed on the data using Fortran-like statements to define the required transformation.
• Specialised extra data columns are provided, i.e. LABCOL for labels, SYMCOL for symbol numbers and EXCOL/EYCOL for errors.
• Many interactive cursor functions are provided.
• Error ellipses can be drawn.
• Vector plots can be drawn.
• Simple statistical analysis of the data is available.
• The data can be resampled.
• Functions defined by Fortran-like statements can be drawn.

PONGO can used from both the Starlink/ICL and IRAF/CL 1 command languages and integrates with other Starlink software packages.

Because the parameters PONGO uses for its commands are often similar to the arguments of the equivalent PGPLOT subroutines, it is useful to read the PGPLOT manual in conjunction with this user guide (if you are not already familiar with PGPLOT). In several cases the full descriptions of the parameters are given only in the PGPLOT manual.

1at the time of writing IRAF support is no longer available in a standard release