Recent changes to chgcentre

chgcentre modified by André Offringa

André Offringa — Sat, 15 Mar 2014 23:17:53 -0000

--- v2
+++ v3
@@ -1,6 +1,6 @@
-The 'chgcentre' tool can be used to change the phase centre of a measurement set. It will recalculate the uvw values (from antenna locatons, phase centre and time) and phase-rotate the visibilities. We found that the casa task 'fixvis' does not do this.
+The 'chgcentre' tool can be used to change the phase centre of a measurement set. It will recalculate the *uvw*-values (from the antenna locations, phase centre and time) and phase-rotate the visibilities. We found that the casa task 'fixvis' has several bugs (as of March 2014), and cannot be used to phase rotate a measurement set properly.

-The compilation of chgcentre is very similar to wsclean's compilation, so see the [general installation instruction](Installation) for help. The chgcentre tool is available as a separate download: see the files section for downloading chgcentre.
+The compilation of chgcentre is very similar to wsclean's compilation. See the [general installation instruction](Installation) for help. The chgcentre tool is available as a separate download. See the files section for downloading chgcentre.

 Execute chgcentre without parameters to get help on the syntax:

chgcentre modified by André Offringa

André Offringa — Sat, 15 Mar 2014 23:15:35 -0000

--- v1
+++ v2
@@ -4,6 +4,8 @@

 Execute chgcentre without parameters to get help on the syntax:

+    :::text
+    $ chgcentre
     A program to change the phase centre of a measurement set.
     Written by André Offringa (offringa@gmail.com).

@@ -19,16 +21,24 @@

 If you do not provide a new RA and dec, chgcentre will give you some info about the measurement set:

-    $ ./chgcentre myobs.ms
+    :::text
+    $ chgcentre myobs.ms
     A program to change the phase centre of a measurement set.
     Written by André Offringa (offringa@gmail.com).

     Current phase direction:
       -00h59m31.7s -16d46m19s
     Zenith is at:
-      -01h00m00.8s -26d46m44s (-01h00m49.0s -26d46m44s - -00h59m12.7s -26d46m44s
+      -01h00m00.8s -26d46m44s (-01h00m49.0s -26d46m44s - -00h59m12.7s -26d46m44s)
     Min-w direction is at:
       -00h59m31.7s -26d46m19s

-You can specify '-zenith' or '-minw' as option to rephase to the local array zenith or the direction orthogonal to the best-fit plane to the antennas. The latter is close to zenith, but provides slightly lower *w*-terms. This has not been tested on telescopes other than the MWA.
+You can specify '-zenith' or '-minw' as option to rephase to the local array zenith or the direction orthogonal to the best-fit plane to the antennas. The latter is close to zenith, but provides slightly lower *w*-terms. This has not been tested on telescopes other than the MWA. The syntax for this is:

+    :::text
+    $ chgcentre -minw myobs.ms
+
+Finally, you can provide option '-shiftback' to prepare the measurement set for w-snapshot imaging with WSClean, using the recentring technique. See the [w-snapshot algorithm page](WSnapshotAlgorithm) for more info. You can specify any phase centre with -shiftback, but the common way to do this would be:
+
+    :::text
+    $ chgcentre -minw -shiftback myobs.ms

chgcentre modified by André Offringa

André Offringa — Sat, 15 Mar 2014 23:11:44 -0000

The 'chgcentre' tool can be used to change the phase centre of a measurement set. It will recalculate the uvw values (from antenna locatons, phase centre and time) and phase-rotate the visibilities. We found that the casa task 'fixvis' does not do this.

The compilation of chgcentre is very similar to wsclean's compilation, so see the general installation instruction for help. The chgcentre tool is available as a separate download: see the files section for downloading chgcentre.

Execute chgcentre without parameters to get help on the syntax:

A program to change the phase centre of a measurement set.
Written by André Offringa (offringa@gmail.com).

Syntax: chgcentre [options] <ms> <new ra> <new dec>

The format of RA can either be 00h00m00.0s or 00:00:00.0
The format of Dec can either be 00d00m00.0s or 00.00.00.0

Example to rotate to HydA:
    chgcentre myset.ms 09h18m05.8s -12d05m44s

When a measurement set contains multiple data columns (e.g., DATA, MODEL_DATA, CORRECTED_DATA), each column will be updated.

If you do not provide a new RA and dec, chgcentre will give you some info about the measurement set:

$ ./chgcentre myobs.ms
A program to change the phase centre of a measurement set.
Written by André Offringa (offringa@gmail.com).

Current phase direction:
  -00h59m31.7s -16d46m19s
Zenith is at:
  -01h00m00.8s -26d46m44s (-01h00m49.0s -26d46m44s - -00h59m12.7s -26d46m44s
Min-w direction is at:
  -00h59m31.7s -26d46m19s

You can specify '-zenith' or '-minw' as option to rephase to the local array zenith or the direction orthogonal to the best-fit plane to the antennas. The latter is close to zenith, but provides slightly lower w-terms. This has not been tested on telescopes other than the MWA.