# Usage of angularSeparationOfDirectionsArcsec

﻿﻿ Accepts two direction dictionaries and returns the separation in arc seconds. It computes great circle angle using the Vincenty formula. See also angularSeparationOfDirections, angularSeparationOfScans, angularSeparationOfStrings, angularSeparationOfPlanets, angularSeparation, angularSeparationRadians, and angularSeparationRadiansTuples.

### Usage:

```au.angularSeparationOfDirectionsArcsec(dir1, dir2, returnComponents=False)
```
By default, it returns only the separation angle. If returnComponents == True, then it returns: [angle, ra_angle, dec_angle, ra_angle*cos(Dec)]

### Examples:

```CASA <15>: ms.open('uid___A002_X1465d3_Xc7.ms')
Out[15]: True
CASA <16>: a=ms.getfielddirmeas(fieldid=0)
CASA <17>: b=ms.getfielddirmeas(fieldid=1)
CASA <18>: au.angularSeparationOfDirectionsArcsec(a,b)
{'type': 'direction', 'm1': {'value': -0.51036394872856283, 'unit': 'rad'}, 'm0': {'value': -1.20056435950273, 'unit': 'rad'}, 'refer': 'J2000'} {'type': 'direction', 'm1': {'value': 0.0, 'unit': 'rad'}, 'm0': {'value': 0.0, 'unit': 'rad'}, 'refer': 'J2000'}
Out[18]:  257744.07107746199

CASA <19>: au.angularSeparationOfDirectionsArcsec(a,b,True)
{'type': 'direction', 'm1': {'value': -0.51036394872856283, 'unit': 'rad'}, 'm0': {'value': -1.20056435950273, 'unit': 'rad'}, 'refer': 'J2000'} {'type': 'direction', 'm1': {'value': 0.0, 'unit': 'rad'}, 'm0': {'value': 0.0, 'unit': 'rad'}, 'refer': 'J2000'}
Out[19]: array([ 257744.07107746, -247634.175, -105270.121, -239615.13098521])
```

-- ToddHunter - 2013-09-09
Topic revision: r1 - 2013-09-09, ToddHunter

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