Introduction

ISOCONT is an IDL¹procedure which allows the user to overlay a contour plot of one image (IMAGE_2), on a color display of another (IMAGE_1). The two input images may come from different instruments, have different sizes and different resolutions. The only requirement is that they spatially overlap, i.e. they have roughly the same astronomical coordinates. ISOCONT was developed in order to facilitate the visualization and analysis of observations made with the ISOCAM infrared camera on-board the ISO² satellite launched by ESA³ The input images can be either in FITS⁴ format or contained in a CIA⁵ raster data structure (raster PDS) or beam-switch data structure (beam-switch PDS). If IMAGE_1 and IMAGE_2 are the same, then a color image is being displayed with an overlay of its own contour levels. Using only one image as input, one can create a nice display along with the astronomical coordinates. The output is displayed in a new IDL window approximately 650 x 650 pixels in size.

In section 2 we describe the formal syntax of ISOCONT. Approximately 30 keywords which modify the default settings are available and they are listed in Table 1. In section 3 we present a brief discussion and a series of several examples on the use of ISOCONT. Most of the examples are accompanied by a postscript figure of the output display. Finally in section 4 we include a brief discussion on FITS format files and the potential problems arising from the lack of a single astrometry standard in the FITS headers.

¹IDL is a registered trademark of Research Systems, Inc.
² Infrared Space Observatory
³European Space Agency
⁴Flexible Image Transport System
⁵ CAM Interactive Analysis