Each attribute has a name, a value, and a state. This application accesses all attribute values as character strings, converting to and from other data types as necessary. The attribute state is a Boolean flag (i.e. TRUE or FALSE) indicating whether or not a value has been assigned to the attribute. If no value has been assigned to an attribute, then it adopts a default value until an explicit value is assigned to it. An attribute value can be cleared, causing the attribute to revert to its default value.
The operation performed by this application is controlled by Parameter MODE, and can:
display the value of an attribute;
set a new value for an attribute;
set new values for a list of attributes;
clear an attribute value; and
test the state of an attribute.
Note, the attributes of the PIXEL, GRID and AXIS Frames are managed internally by the NDF library. They may be examined using this application, but an error is reported if any attempt is made to change them. The exception to this is that the Domain attribute may be changed, resulting in a copy of the Frame being added to the WCS component of the NDF with the new Domain name. The AXIS Frame is derived from the AXIS structures within the NDF, so the AXLABEL and AXUNITS commands may be used to change the axis label or units string for the AXIS Frame.
"Clear" –- Clears the current attribute value, causing it to revert to its default
"Get" –- The current value of the attribute is displayed on the screen and written to
output Parameter VALUE. If the attribute has not yet been assigned a value (or has been
cleared), then the default value will be displayed.
"MSet" –- Assigns new values to multiple attributes. The attribute names and values are
obtained using Parameter SETTING.
"Set" –- Assigns a new value, given by Parameter NEWVAL, to the attribute.
"Test" –- Displays
"TRUE" if the attribute has been assigned a value, and
otherwise (in which case the attribute will adopt its default value). This flag is
written to the output Parameter STATE.
The initial suggested default is
"Get", the access is Read only.
"Clear". If REMAP is
TRUE, then the Mappings which connect the current Frame to the other Frames within the WCS FrameSet will be modified (if necessary) to maintain the FrameSet integrity. For instance, if the current Frame of the NDF represents FK5 RA and DEC, and you change System from
"Galactic", then the Mappings which connect the SKY Frame to the other Frames (e.g. PIXEL, AXIS) will be modified so that each pixel corresponds to the correct Galactic co-ordinates. If REMAP is
FALSE, then the Mappings will not be changed. This can be useful if the FrameSet has incorrect attribute values for some reason, which need to be corrected without altering the Mappings to take account of the change.
"MSet". It should hold a comma-separated list of
<attribute>is the name of an attribute and
<value>is the value to assign to the attribute.
"Polarization map of Centaurus-A".
"TRUE"if a value has been set for the Label attribute for the first axis of the current co-ordinate Frame in the NDF called my_data, and
"my_data"has been set to some incorrect value, which needs to be corrected to
"J2000". The REMAP parameter is set
FALSE, which prevents the inter-Frame Mappings from being altered to take account of the new Equinox value. This means that each pixel in the NDF will retain its original RA and DEC values (but they will now be interpreted as J2000). If REMAP had been left at its default value of
TRUE, then the RA and DEC associated with each pixel would have been modified in order to precess them from the original (incorrect) equinox to J2000.
An error is reported if an attempt is made to set or clear the Base Frame in the WCS component.
The Domain names GRID, FRACTION, AXIS, and PIXEL are reserved for use by the NDF library and an error will be reported if an attempt is made to assign one of these values to any Frame.