A string determining the co-ordinate Frame in which positions are to be stored in the output catalogue associated with Parameter OUTCAT. See Parameter FRAME for a description of the allowed values for this parameter. If a null (!) value is supplied, the positions will be stored the Frame used to specify positions within the input catalogue. [!]

The epoch at which the sky positions stored in the output catalogue were determined. It will only be accessed if an epoch value is needed to qualify the co-ordinate Frame specified by COLFRAME. If required, it should be given as a decimal-years value, with or without decimal places ("1996.8", for example). Such values are interpreted as a Besselian epoch if less than 1984.0 and as a Julian epoch otherwise.

This parameter is only accessed if Parameter PLOT is set to "Chain" or "Poly". If TRUE, polgons will be closed by joining the first position to the last position. [current value]

The NDF array component to be displayed if a non-null value is supplied for Parameter NDF. It may be "Data", "Variance", "Error", or "Quality". ["Data"]

If TRUE, a detailed description of the co-ordinate Frame in which the positions will be reported is displayed before the positions. [current value]

The graphics workstation. Only accessed if Parameter PLOT indicates that graphics are required. [current graphics device]

If an IRAS90 Sky Co-ordinate System specification is supplied (using Parameter FRAME) for a celestial co-ordinate system, then an epoch value is needed to qualify it. This is the epoch at which the supplied sky positions were determined. It should be given as a decimal years value, with or without decimal places ("1996.8" for example). Such values are interpreted as a Besselian epoch if less than 1984.0 and as a Julian epoch otherwise.

The identifier for the first position to be displayed. Positions are only displayed which have identifiers in the range given by Parameters FIRST and LAST. If a null (!) value is supplied, the value used is the lowest identifier value in the positions list. [!]

A string determining the co-ordinate Frame in which positions are to be reported. This application can report positions in any of the co-ordinate Frames stored with the positions list. The string supplied for FRAME can be one of the following.

• A domain name  such as SKY, AXIS, PIXEL.

• An integer value giving the index of the required Frame.

• An IRAS90 Sky Co-ordinate System (SCS) values such as "EQUAT(J2000)" (see SUN/163).

If a null value (!) is supplied, positions are reported in the co-ordinate Frame which was current when the positions list was created. The user is re-prompted if the specified Frame is not available within the positions list. The range of Frames available will include all those read from the supplied positions list. In addition, if a graphics device is opened (i.e. if Parameter PLOT is set to anything other than "None"), then all the Frames associated with the picture specified by Parameter NAME will also be available. [!]

This parameter is only accessed if Parameter PLOT is set to "Chain" or "Poly". It specifies whether the curves drawn between positions should be stright lines, or should be geodesic curves. In many co-ordinate Frames geodesic curves will be simple straight lines. However, in others (such as the majority of celestial co-ordinate Frames) geodesic curves will be more complex curves tracing the shortest path between two positions in a non-linear projection. [FALSE]

A catalogue containing a positions list such as produced by applications LISTMAKE and CURSOR.

A string specifying the justification to be used when displaying text strings at the supplied positions. This parameter is only accessed if Parameter PLOT is set to "Text". The supplied string should contain two characters; the first should be "B", "C", or "T", meaning bottom, centre, or top respectively. The second should be "L", "C", or "R", meaning left, centre, or right respectively. The text is displayed so that the supplied position is at the specified point within the displayed text string. [CC]

If TRUE the positions are labelled on the graphics device specified by Parameter DEVICE. The offset of the centre of each label from the corresponding position is controlled using the NumLabGap(1)  and NumLabGap(2) plotting attributes, and the appearance of the labels is controlled using attributes Colour(NumLab), Size(NumLab), etc. These attributes may be specified using Parameter STYLE. The content of the label is determined by Parameter LABTYPE. [FALSE]

Determines what sort of labels are drawn if the LABEL parameter is set TRUE. It can be either of the following.

• "ID" –- causes the integer identifier associated with each row to be used as the label for the row.

• "LABEL" –- causes the textual label associated with each row to be used as the label for the row. These strings are read from the "LABEL" column of the supplied catalogue.

If a null (!) value is supplied, a default of "LABEL" will be used if the input catalogue contains a "LABEL" column. Otherwise, a default of "ID" will be used. [!]

The identifier for the last position to be displayed. Positions are only displayed which have identifiers in the range given by Parameters FIRST and LAST. If a null (!) value is supplied, the value used is the highest identifier value in the positions list. [!]

The name of the text file in which the formatted co-ordinates of the selected positions may be stored. This is intended primarily for recording the screen output, and not for communicating positions to subsequent applications. A null string (!) means that no file is created. [!]

This parameter is only accessed if Parameter PLOT is set to "Chain" or "Mark". It specifies the type of marker with which each position should be marked, and should be given as an integer PGPLOT marker type. For instance, 0 gives a box, 1 gives a dot, 2 gives a cross, 3 gives an asterisk, 7 gives a triangle. The value must be larger than or equal to $-$31. [current value]

The method to use when sampling the input NDF (if any) specified by Parameter NDF at each of the positions in the catalogue. For details on these schemes, see the description of routine AST_RESAMPLEx in SUN/210. Note, "Nearest" is always used if Parameter COMP is "Quality" . METHOD can take the following values.

• "Bilinear" –- The displayed pixel values are calculated by bi-linear interpolation among the four nearest pixels values in the input NDF. This produces smoother output NDFs than the nearest-neighbour scheme, but is marginally slower.

• "Nearest" –- Each displayed pixel value is the value of the nearest input pixel.

• "Sinc" –- Uses the $\mathrm{\text{sinc}}\left(\pi x\right)$ kernel, where $x$ is the pixel offset from the interpolation point, and $\mathrm{\text{sinc}}\left(z\right)=sin\left(z\right)/z$. Use of this scheme is not recommended.

• "SincSinc" –- Uses the $\mathrm{\text{sinc}}\left(\pi x\right)\mathrm{\text{sinc}}\left(k\pi x\right)$ A valuable general-purpose scheme, intermediate in its visual effect on NDFs between the bi-linear and nearest-neighbour schemes.

• "SincCos" –- Uses the $\mathrm{\text{sinc}}\left(\pi x\right)cos\left(k\pi x\right)$ kernel. Gives similar results to the "SincSinc" scheme.

• "SincGauss" –- Uses the $\mathrm{\text{sinc}}\left(\pi x\right)e^{-k{x}^2}$ kernel. Good results can be obtained by matching the FWHM of the envelope function to the point-spread function of the input data (see Parameter PARAMS).

• "Somb" –- Uses the $\mathrm{\text{somb}}\left(\pi x\right)$ kernel, where $x$ is the pixel offset from the interpolation point, and $\mathrm{\text{somb}}\left(z\right)=2\ast J_1\left(z\right)/z$. $J_1$ is the first-order Bessel function of the first kind. This scheme is similar to the "Sinc" scheme.

• "SombCos" –- Uses the $\mathrm{\text{somb}}\left(\pi x\right)cos\left(k\pi x\right)$ kernel. This scheme is similar to the "SincCos" scheme.

• "Gauss" –- Uses the $e^{-k{x}^2}$ kernel. The FWHM of the Gaussian is given by Parameter PARAMS(2), and the point at which to truncate the Gaussian to zero is given by Parameter PARAMS(1).

The initial default is " Nearest" . [current value]

Determines the graphics database picture with which the supplied positions are to be aligned. Only accessed if Parameter PLOT indicates that some graphics are to be produced. A search is made for the most recent picture with the specified name (e.g. DATA, FRAME or KEY) within the current picture. If no such picture can be found, or if a null value is supplied, the current picture itself is used. The name BASE can also be supplied as a special case, which causes the BASE picture to be used even though it will not in general fall within the current picture. ["DATA"]

If an NDF is supplied, the values within the NDF at the positions specified in the input catalogue are displayed on the screen and written to Output Parameter PIXVALS. The displayed values are calculated by interpolating between the NDF pixel values using the interpolation method specified by Parameter METHOD. The NDF array component to be displayed is specified by Parameter COMP. [!]

The output catalogue in which to store the selected positions. If a null value is supplied, no output catalogue is produced. See Parameter COLFRAME. [!]

An optional array which consists of additional parameters required by the Sinc, SincSinc, SincCos, SincGauss, Somb, SombCos, and Gauss methods (see Parameter METHOD).

PARAMS( 1 ) is required by all the above schemes. It is used to specify how many pixels are to contribute to the interpolated result on either side of the interpolation or binning point in each dimension. Typically, a value of 2 is appropriate and the minimum allowed value is 1 (i.e. one pixel on each side). A value of zero or fewer indicates that a suitable number of pixels should be calculated automatically. [0]

PARAMS( 2 ) is required only by the Gauss, SombCos, SincSinc, SincCos, and SincGauss schemes. For the SombCos, SincSinc, and SincCos schemes, it specifies the number of pixels at which the envelope of the function goes to zero. The minimum value is 1.0, and the run-time default value is 2.0. For the Gauss and SincGauss schemes, it specifies the full-width at half-maximum (FWHM) of the Gaussian envelope measured in output pixels. The minimum value is 0.1, and the run-time default is 1.0. On astronomical NDFs and spectra, good results are often obtained by approximately matching the FWHM of the envelope function, given by PARAMS(2), to the point-spread function of the input data. []

The type of graphics to be used to mark the positions on the graphics device specified by Parameter DEVICE. The appearance of these graphics (colour, size, etc.) is controlled by the STYLE parameter. PLOT can take any of the following values.

• "None" –- No graphics are produced.

• "Mark" –- Each position is marked with a marker of type specified by Parameter MARKER.

• "Poly" –- Causes each position to be joined by a line to the previous position. These lines may be simple straight lines or geodesic curves (see Parameter GEODESIC). The polygons may optionally be closed by joining the last position to the first (see Parameter CLOSE).

• "Chain" –- This is a combination of "Mark" and "Poly". Each position is marked by a marker and joined by a line to the previous position. Parameters MARKER, GEODESIC, and CLOSE are used to specify the markers and lines to use.

• "Box" –- A rectangular box with edges parallel to the edges of the graphics device is drawn between each pair of positions.

• "Vline" –- A vertical line is drawn through each position, extending the entire height of the selected picture.

• "Hline" –- A horizontal line is drawn through each position, extending the entire width of the selected picture.

• "Cross" –- A combination of "Vline" and "Hline".

• "STCS" –- Indicates that each position should be marked using the two-dimensional STC-S shape read from the catalogue column specified by Parameter STCSCOL.

• "Text" –- A text string is used to mark each position. The string is drawn horizontally with the justification specified by Parameter JUST. The strings to use for each position are specified using Parameter STRINGS.

• "Blank" –- The graphics device is opened and the picture specified by Parameter NAME is found, but no actual graphics are drawn to mark the positions. This can be useful if you just want to transform the supplied positions into one of the co-ordinate Frames associated with the picture, without drawing anything (see Parameter FRAME).

Each position may also be separately labelled with its integer identifier value by giving a TRUE value for Parameter LABEL. ["None"]

The unformatted co-ordinates of the positions selected by Parameters FIRST and LAST, in the co-ordinate Frame selected by FRAME. The axis values are stored as a one-dimensional vector. All the Axis-1 values for the selected positions are stored first, followed by the Axis-2 values, etc. The number of positions in the vector is written to the output Parameter NUMBER, and the number of axes per position is written to the output Parameter DIM. The axis values may not be in the same units as the formatted values shown on the screen. For instance, unformatted celestial co-ordinate values are stored in units of radians.

The increment between position identifiers to be displayed. Specifying a value larger than 1 causes a subset of the position identifiers between FIRST and LAST to be displayed. [1]

The name of a catalogue column containing an STC-S description of a two-dimensional spatial shape associated with each position. The STC-S format is an IVOA proposal for describing regions of space, time and spectral position. For further details, see the STC-S document on the IVOA web site (http://www.ivoa.net/Documents/). An STC-S description of a shape includes the co-ordinate system in which the shape is defined. This application assumes that all the STC-S shapes read from the specified column will be defined within the same co-ordinate system. The transformation from the STC-S co-ordinate system to the co-ordinate system of the displayed image is determined once from the first shape plotted, and then re-used for all later shapes. ["Shape"]

A group of text strings which are used to mark the supplied positions if Parameter PLOT is set to "Text". The first string in the group is used to mark the first position, the second string is used to mark the second position, etc. If more positions are given than there are strings in the group, then the extra positions will be marked with an integer value indicating the index within the list of supplied positions. (Note, these integers may be different from the identifiers in the supplied positions list). If a null value (!) is given for the parameter, then all positions will be marked with the integer indices, starting at 1.

A comma-separated list should be given in which each element is either a marker string, or the name of a text file preceded by an up-arrow character "$$^". Such text files should contain further comma-separated lists which will be read and interpreted in the same manner. Note, strings within text files can be separated by new lines as well as commas.

A group of attribute settings describing the style to use when formatting the co-ordinate values displayed on the screen, and when drawing the graphics specified by Parameter PLOT.

A comma-separated list of strings should be given in which each string is either an attribute setting, or the name of a text file preceded by an up-arrow character "$$^". Such text files should contain further comma-separated lists which will be read and interpreted in the same manner. Attribute settings are applied in the order in which they occur within the list, with later settings overriding any earlier settings given for the same attribute.

Each individual attribute setting should be of the form:

$<$name$>$=$<$value$>$

where $<$name$>$ is the name of a plotting attribute, and $<$value$>$ is the value to assign to the attribute. Default values will be used for any unspecified attributes. All attributes will be defaulted if a null value (!)–-the initial default–-is supplied. To apply changes of style to only the current invocation, begin these attributes with a plus sign. A mixture of persistent and temporary style changes is achieved by listing all the persistent attributes followed by a plus sign then the list of temporary attributes.

See Section E for a description of the available attributes. Any unrecognised attributes are ignored (no error is reported).

In addition to the attributes which control the appearance of the graphics (Colour, Font, etc.), the following attributes may be set in order to control the appearance of the formatted axis values reported on the screen: Format, Digits, Symbol, Unit. These may be suffixed with an axis number (e.g. Digits(2)) to refer to the values displayed for a specific axis. [current value]

The number of axes for each position written to output Parameter POSNS.

The number of positions selected.

The pixel values at the listed positions. Only used if a non-null value is supplied for Parameter NDF.