### The UV_PREVIEW command

With large datasets, imaging can be long. IMAGER offers a simple, fast pre-imaging viewer through command UV_PREVIEW.

This command will display the spectra obtained towards the phase center at several spatial scales (the default is for 4 tapers). It will also attempt to detect spectral features, by analyzing for each spectrum the noise statistics and the outliers. It performs automatic line identifications, using database(s) in the LINEDB\ or ASTRO data format selected by command CATALOG. Potential spectral lines in the band are displayed in blue, and detected ones in red. UV_PREVIEW also warns the user about improper scaling of the data weights. The line emission region is indicated in grey.

The result of this automatic signal detection and line identification is saved in a SIC structure named PREVIEW%, that is automatically used by commands UV_BASELINE /CHANNELS and UV_FILTER /CHANNELS to respectively remove the continuum and filter the line emission to produce a continuum data set. The detected line frequencies are stored in PREVIEW%FOUND%FREQ and their names in PREVIEW%FOUND%LINES. This can be used to reference the velocity scale of the data to one of the detected lines, by using command SPECIFY FREQUENCY 'PREVIEW%FOUND%FREQ[1]' for example before further processing.

An example is shown in Fig

Figure: The UV_PREVIEW output