fv: Features

fv is a general-purpose FITS file editor (formerly just a file viewer) able to manipulate virtually all aspects of a FITS file and perform basic data analysis of its contents.

(Highlighted items are new to release 3.2.)

• fv runs under most major operating systems: Unix/Linux, Windows, and Mac OS.
• Basic fv functions -- open, display, plot data, sort, save, close -- can be accessed from simple TCL scripts. With the XPA package (available separately from SAO) for unix, fv can be controlled by other programs. On Mac OS, fv can be controlled with AppleScript. Sample programs written using XPA (C, Tcl, and Csh), Tcl, and AppleScript are included.
• Files can be opened (read-only) across the internet (http and ftp protocols). FTP sites can be browsed from the "Open File" dialog box.
• The SkyView online database can be searched for images of and object lists for a region of the sky. Results are downloaded in FITS format which then can be plotted.
• Filename completion eases browsing large directories and typing long names... type the first few letters of a filename and then hit TAB.

• A summary window lists the contents and size of all the extensions in the FITS file. Entire extensions can be copied, cut, and pasted to/from the clipboard which can be saved to a new FITS file. New, empty FITS files can be created. Empty extensions of any of the 3 basic types -- image, ASCII table, and binary table -- can be appended to existing files.
• New function buttons have been added to the File Summary window to provide short cuts to common operations:

   - 'Hist' - displays a histogram image of 1 or 2 columns in a table
   - 'Plot' - plots table columns
   - 'Table All' and 'Table Select'
      - The first button displays all the columns in a table, whereas the
        second button allows the user to select which columns to display.  

• When displaying Hierarchical grouping tables, a new 'OPEN' button is available at the beginning of each row which can be used to open the corresponding group member file.
• Can display and edit images that are compressed with the new FITS 'Tile Compression' algorithm.
• FITS headers may be displayed in a scrolling text window. Keywords may be edited, inserted, or deleted, and an ASCII text listing of the header may be generated. Checksum keywords can be created or updated when a file is modified.

• Selected columns in a FITS table may be viewed in a scrolling spreadsheet. The values in the table may be edited, and rows and columns may be inserted or deleted in the table. Tables can be sorted using multiple keys and rows with identical keys optionally deleted. Table rows can be selectively deleted using a boolean expression evaluated for each row. The contents of a table may be saved to an ASCII text file.
• Line plots of one or more columns (or arithmetic expressions involving one or more columns) in a table may be generated and displayed in the POW widget. Data can be extracted from a subset of rows; each row of a vector column can be plotted as a separate curve. Individual columns or pairs of columns can be used to produce 1D or 2D histograms, respectively, and plotted in POW.
• A spreadsheet calculator function allows you to create new columns by performing arithmetic on existing columns.
• FITS images may be displayed with the usual pan, zoom, and color table manipulation facilities. Users may choose to use the SAOtng or DS9 image display tools (available separately from SAO), or the internal image display widget called POW that is supplied with fv. Double clicking an image displayed by POW will bring up a fv table of the image data with the clicked pixel highlighted.
• FITS image data also may be displayed as a table, allowing individual pixels to be edited. Selected rows or columns can be averaged and their pixels plotted in a line graph. Image data can be smoothed using a boxcar filter.
• On Unix machines with FTOOLS installed, one can select and execute an FTOOL from within fv.
• An optional "Desktop Manager" allows for management of the various fv windows.

POW is a general-purpose graphing widget which can display and manipulate line plots and images.

(Highlighted items are new to release 3.0.)

• Graphs can be repositioned and resized, and regions of interest can be zoomed in on. The cursor's position within a graph and, for images, the pixel's value located there are displayed in a continuously-updated readout.

• An image's colortable (i.e. contrast and bias) can be interactively manipulated. More than 20 different color schemes can be selected.
• Histogram Equalization colormap intelligently distributes the colormap according to the distribution of pixel intensities in an image.
• POW supports TrueColor displays and has more "X colormap friendly" support for PsuedoColor display. See the documentation for the "-cmap" fv command line switch or the POW "Color" help menu item for details.
• POW interprets standard FITS World Coordinate System (WCS) keywords, and optionally displays grid lines.
• Text labels can be placed on a graph at a position fixed either to the graph (eg, a legend) or to the graph's coordinate system (eg, an object label).
• Font, size, and style of labels can be independently controlled for graph titles, axis labels, tick labels, and each text label.
• Once displayed in POW, the contents of graphs can be edited and multiple graphs can be merged into one. Coordinate information (labels, pixel sizes, WCS parameters, etc) can be modified as well.
• Multiple images can be mosaiced within a single graph. The only restriction is that the images have identical rotations. (Well-separated WCS images will not be projected exactly, though.)
• A single intuitive dialog box controls virtually all aspects of a graph, from its contents and labels, to the tick mark spacing, to the display options of its curves, to the colormaps of its images.
• Each curve plotted in a graph can be displayed in a number of line styles/widths, point shapes/sizes, and colors. The color of a curve's points and connecting lines can have different colors. Graphs containing multiple curves will have different colors assigned to each curve.
• Log and semi-log graphs can be created from either logarithmic or regular curve data.
• POW can create, read, write, and graphically manipulate regions (boxes, circles, ellipses, polygons, lines, and points). Supports new DS9 region file format.
• POW can "blink" a set of images or graphs in rapid sequence. A 3D image cube can be animated in this manner.
• POW can create contour maps of images.
• Measure the distance between two points on a graph using the Ruler tool.
• Flux and centroid values for a region of an image can be calculated with the Probe tool.
• Plot an image cross-section with the Profile tool.
• A standalone tool, POWplot, can be used to display a single image without going through fv.

See the release notes for details on the changes from the previous version.