TRUE if labelled and annotated axes are to be drawn around the contour map, showing the current co-ordinate Frame of the supplied NDF. The appearance of the axes can be controlled using the STYLE parameter. If a null (!) value is supplied, then axes will be drawn unless the CLEAR parameter indicates that the graphics device is not being cleared. [!]

TRUE if the graphics device is to be cleared before displaying the contour map. If you want the contour map to be drawn over the top of an existing DATA picture, then set CLEAR to FALSE. The contour map will then be drawn in alignment with the displayed data. If possible, alignment occurs within the current co-ordinate Frame of the NDF. If this is not possible, (for instance if suitable WCS information was not stored with the existing DATA picture), then alignment is attempted in PIXEL co-ordinates. If this is not possible, then alignment is attempted in GRID co-ordinates. If this is not possible, then alignment is attempted in the first suitable Frame found in the NDF irrespective of its domain. A message is displayed indicating the domain in which alignment occurred. If there are no suitable Frames in the NDF then an error is reported. [TRUE]

The NDF component to be contoured. It may be "Data", "Quality", "Variance", or "Error" (where "Error" is an alternative to "Variance" and causes the square root of the variance values to be displayed). If "Quality" is specified, then the quality values are treated as numerical values (in the range 0 to 255). ["Data"]

The height below which the contours will be drawn with dashed lines (if possible). A null value (!) results in contours being drawn with the styles specified by Parameters PENS, PENROT, and STYLE. [!]

The plotting device. [current graphics device]

If TRUE, then a faster, but in certain cases less-accurate, method is used to draw the contours. In fast mode, contours may be incorrectly placed on the display if the mapping between graphics co-ordinates and the current co-ordinate Frame of the supplied NDF has any discontinuities, or is strongly non-linear. This may be the case, for instance, when displaying all-sky maps on top of each other. [TRUE]

The contour plot normally has square pixels, in other words a specified length along each axis corresponds to the same number of pixels. However, for images with markedly different dimensions this default behaviour may not be suitable or give the clearest plot. When FILL is TRUE, the square-pixel constraint is relaxed and the contour plot is the largest possible within the current picture. When FILL is FALSE, the pixels are square. [FALSE]

Height of the first contour (Linear and Magnitude modes).

The required contour levels (Free mode).

TRUE if a key of the contour level versus pixel value is to be produced. The appearance of this key can be controlled using Parameter KEYSTYLE, and its position can be controlled using Parameter KEYPOS. [TRUE]

Two values giving the position of the key. The first value gives the gap between the right-hand edge of the contour map and the left-hand edge of the key (0.0 for no gap, 1.0 for the largest gap). The second value gives the vertical position of the top of the key (1.0 for the highest position, 0.0 for the lowest). If the second value is not given, the top of the key is placed level with the top of the contour map. Both values should be in the range 0.0 to 1.0. If a key is produced, then the right-hand margin specified by Parameter MARGIN is ignored. [current value]

A group of attribute settings describing the plotting style to use for the key (see Parameter KEY).

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).

The heading in the key can be changed by setting a value for the Title attribute (the supplied heading is split into lines of no more than 17 characters). The appearance of the heading is controlled by attributes Colour(Title), Font(Title), etc. The appearance of the contour indices is controlled by attributes Colour(TextLab), Font(TextLab), etc. (the synonym Index can be used in place of TextLab). The appearance of the contour values is controlled by attributes Colour(NumLab), Font(NumLab), etc. (the synonym Value can be used in place of NumLab). Contour indices are formatted using attributes Format(1), Digits(1), etc. (the synonym Index can be used in place of value 1). Contour values are formatted using attributes Format(2), etc. (the synonym Value can be used in place of the value 2). [current value]

Only used if Parameter MODE is set to "Good" or "Bounds". It specifies the position at which to place a label identifying the input NDF within the plot. The label is drawn parallel to the first pixel axis. Two values should be supplied for LABPOS. The first value specifies the distance in millimetres along the first pixel axis from the centre of the bottom-left pixel to the left edge of the label. The second value specifies the distance in millimetres along the second pixel axis from the centre of the bottom-left pixel to the baseline of the label. If a null (!) value is given, no label is produced. The appearance of the label can be set by using the STYLE parameter (for instance "Size(strings)=2"). [current value]

Height of the last contour (Linear and Magnitude modes).

The widths of the margins to leave around the contour map for axis annotation. The widths should be given as fractions of the corresponding dimension of the current picture. The actual margins used may be increased to preserve the aspect ratio of the DATA picture. Four values may be given, in the order; bottom, right, top, left. If fewer than four values are given, extra values are used equal to the first supplied value. If these margins are too narrow any axis annotation may be clipped. If a null (!) value is supplied, the value used is 0.15 (for all edges) if annotated axes are being produced, and zero otherwise. See also Parameter KEYPOS. [current value]

The method used to select the contour levels. The options are:

• "Area" –- The contours enclose areas of the array for which the equivalent radius increases by equal increments. You specify the number of levels.

• "Automatic" –- The contour levels are equally spaced between the maximum and minimum pixel values in the array. You supply the number of contour levels.

• "Bounds" –- A single ‘contour’ is drawn representing the bounds of the input array. A label may also be added (see Parameter LABPOS).

• "Equalised" –- You define the number of equally spaced percentiles.

• "Free" –- You specify a series of contour values explicitly.

• "Good" –- A single ‘contour’ is drawn outlining the good pixel values. A label may also be added (see Parameter LABPOS).

• "Linear" –- You define the number of contours, the start contour level and linear step between contours.

• "Magnitude" –- You define the number of contours, the start contour level and step between contours. The step size is in magnitudes so the nth contour is dex(-0.4$\ast$(n-1)$\ast$step) times the start contour level.

• "Percentiles" –- You specify a series of percentiles.

• "Scale" –- The contour levels are equally spaced between two pixel values that you specify. You also supply the number of contour levels, which must be at least two.

If the contour map is aligned with an existing DATA picture (see Parameter CLEAR), then only part of the supplied NDF may be displayed. In this case, the choice of contour levels is based on the data within a rectangular section of the input NDF enclosing the existing DATA picture. Data values outside this section are ignored.

The number of contours to draw (only required in certain modes). It must be between 1 and 50. If the number is large, the plot may be cluttered and take longer to produce. The initial suggested default of 6 gives reasonable results.

NDF structure containing the two-dimensional image to be contoured.

If TRUE, the plotting pens are cycled through the contours to aid identification of the contour heights. Only accessed if pen definitions are not supplied using Parameter PENS. [FALSE]

A group of strings, separated by semicolons, each of which specifies the appearance of a pen to be used to draw a contour. The first string in the group describes the pen to use for the first contour, the second string describes the pen for the second contour, etc. If there are fewer strings than contours, then the supplied pens are cycled through again, starting at the beginning. Each string should be a comma-separated list of plotting attributes to be used when drawing the contour. For instance, the string "width=10.0,colour=red,style=2" produces a thick, red, dashed contour. Attributes that are unspecified in a string default to the values implied by Parameter STYLE. If a null value (!) is given for PENS, then the pens implied by Parameters PENROT, DASHED and STYLE are used. [!]

Contour levels given as percentiles. The values must lie between 0.0 and 100.0. (Percentiles mode).

If TRUE, the LENGTH and NUMBER statistics are computed. [FALSE].

Separation between contour levels, linear for Linear mode and in magnitudes for Magnitude mode.

A group of attribute settings describing the plotting style to use for the contours and annotated axes.

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).

The appearance of the contours is controlled by the attributes Colour(Curves), Width(Curves), etc. (the synonym Contours may be used in place of Curves). The contour appearance established in this way may be modified using Parameters PENS, PENROT and DASHED. [current value]

USEAXIS is only accessed if the current co-ordinate Frame of the NDF has more than two axes. A group of two strings should be supplied specifying the two axes which are to be used when annotating and aligning the contour map. Each axis can be specified using one of the following options.

• Its integer index within the current Frame of the input NDF (in the range 1 to the number of axes in the current Frame).

• Its Symbol  string such as "RA" or "VRAD".

• A generic option where "SPEC" requests the spectral axis, "TIME" selects the time axis, "SKYLON" and "SKYLAT" picks the sky longitude and latitude axes respectively. Only those axis domains present are available as options.

A list of acceptable values is displayed if an illegal value is supplied. If a null (!) value is supplied, the axes with the same indices as the two significant NDF pixel axes are used. [!]

On exit this holds the total length in pixels of the contours at each selected height. These values are only computed when Parameter STATS is TRUE.

On exit this holds the number of closed contours at each selected height. Contours are not closed if they intersect a bad pixel or the edge of the image. These values are only computed when Parameter STATS is TRUE.