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image.coordmeasures - Function

	Package	general
	Module	images
	Tool	image

Convert from pixel to world coordinate wrapped as Measures

Synopsis
coordmeasures(pixel, intensity, direction, frequency, velocity)

Arguments

pixel	in	Absolute pixel coordinate
		Allowed:	Numeric vector
		Default:	Reference pixel
intensity	out	Returned intensity quantity for pixel
		Allowed:	Quantity
direction	out	Returned direction measure for pixel
		Allowed:	Direction measure
frequency	out	Returned frequency measure for pixel
		Allowed:	Frequency measure
velocity	out	Returned radial velocity measure for pixel
		Allowed:	Radio definition RadialVelocity measure

Returns
Glish record or fail

Description

You can use this function to get the world coordinates for a specified absolute pixel coordinate in the image. You specify a pixel coordinate (1-rel) for each axis in the image.

If you supply fewer pixel values then there are axes in the image, your value will be padded out with the reference pixel for the missing axes. Excess values will be ignored.

The world coordinate is returned as a record of measures. This function is just a wrapper for toworld (invoked with argument format='m'. Please see its documentation for discussion about the formatting and meaning of the measures.

This Image tool function adds two additional fields to the return record.

The mask field contains the value of the image pixel mask at the specified position. It is either T (pixel is good) or F (pixel is masked as bad or the specified position was off the image).

The intensity field contains the value of the image (at the nearest pixel to that given) and its units. This is actually stored as a Quantity. This field does not exist if the specified pixel coordinate is off the image.

Example

- im := image('myimage')
- meas := im.coordmeasures(im.shape()/2)     
- field_names(meas)                           # Names of measures fields in record
intensity mask direction 
- print meas.intensity
[value=-0.1478955, unit=JY/BEAM]
- print meas.direction
[type=direction, refer=J2000, m1=[value=-0.505949617, unit=rad], 
- m0=[unit=rad, value=-1.64713591]] 
-
- dir := meas.direction                      # Get direction coordinate
-
- dm.doframe(dm.observatory('ATCA'))         # Set location on earth
T
- dm.doframe(dm.epoch('utc', '16jun1999/12:30:20'))   # Set epoch
T
- azel := dm.measure(dir, 'azel')            # Convert to azimuth/elevation
- 
- print 'az,el=', dq.angle(azel.m0), dq.angle(azel.m1)     # Format nicely
az,el= +092.54.56.777 +068.59.59.576

In this example we first find the world coordinates of the centre of the image. Then we use the default Measures tool dm to convert the direction coordinate field from J2000 to an azimuth and elevation at a particular location at a particular time.