
.ti -4
2 BEAM__STEP

  BEAM__STEP   Integer

Number of channels per synthesized beam plane.

Default is 0, meaning only 1 beam plane for all channels.
N (>0) indicates N consecutive channels will share the same dirty beam.

A value of -1 can be used to compute the number of channels per beam plane
that ensures that the angular scale does not deviate more than a fraction
of the map cell at the map edge. This fraction is controlled by
variable MAP__PRECIS (default 0.1)

.ti -4
2 MAP__CELL

      MAP__CELL[2]    Real

The map pixel size [arcsec]. It is recommended to use identical values in X
and Y.  A sampling of at least 5 pixel per beam is recommended to ease the
deconvolution. Enter 0,0 to let the task find the best values.

.ti -4
2 MAP__CENTER

      MAP__CENTER     Character String

Specify the Map center and orientation in the same way as the arguments
of UV__MAP. 
.nf
  LET MAP__CENTER "ANGLE AngleValue"   ! Rotation angle
  LET MAP__CENTER "Ax Ay Unit"         ! Center position 
.fi
where Unit is any of DEGREE, MINUTE, SECOND, RADIAN or ABSOLUTE.
These two possibilities can be combined in any order:
.nf
  LET MAP__CENTER "ANGLE AngleValue Ax Ay Unit" 
  LET MAP__CENTER "Ax Ay Unit ANGLE AngleValue"         
.fi
In the latter case, the keyword ANGLE can be omitted.

For Unit ABSOLUTE, Ax Ay should be the RA and Dec in standard sexagesimal
notation. As usual in SIC, keywords can be abbreviated provided
they are not ambiguous. 

.ti -4
2 MAP__CONVOLUTION

    MAP__CONVOLUTION    Integer

Select the desired convolution function for gridding  in  the  UV  plane
Choices are
.nf
        0    Default (currently 5)
        1    Boxcar
        2    Gaussian
        3    Sin(x)/x
        4    Gaussian * Sin(x)/x
        5    Spheroidal
.fi
Spheroidal functions is the optimal choice. So we strongly discourage use
of any other convolution function, which are here for tests only.

.ti -4
2 MAP__FIELD

  MAP__FIELD[2]     Real

Field of view in X and Y in arcsec.  The field of view MAP__FIELD has
precedence over the number of pixels MAP__SIZE to define the actual
map size when both are non-zero.

.ti -4
2 MAP__POWER

  MAP__POWER[2]     Integer
  
Maximum exponent of 3 and 5 allowed in automatic guess of MAP__SIZE.
MAP__SIZE is decomposed in 2^k 3^p 5^q, and p and q must be less or
equal to MAP__POWER.

Default is 0: MAP__SIZE is just a power of 2. A value of 1 allows
approximation of any map size to 20 %, while a value of 2 allows
10 % approximation. Fast Fourier Transform are slightly slower with
powers of 3 and 5, but limiting the map size can gain a lot in the
Cleaning process (which can scale as MAP__SIZE^4). 


.ti -4
2 MAP__PRECIS

  MAP__PRECIS    Real

Maximum mismatch in pixel at map edge between the true synthesized beam
(which would have been computed using the exact channel frequency) and the
computed synthesized beam with the mean frequency of the channels sharing
the same beam. This is used (with the actual image size) to derive the
actual number of channels that can share the same beam, i.e. the
effective value of BEAM__STEP when BEAM__STEP is -1.

Default is 0.1

.ti -4
2 MAP__ROBUST

  MAP__ROBUST     Real

Robust weighting factor. A number between 0 and +infty.  

Robust weighting gives the natural weight to UV cells whose
natural weight is lower than a given threshold. In contrast, if the natural
weight of the UV cell is larger than this threshold, the weight is set to
this (uniform) threshold. The UV cell size is defined by MAP__UVCELL and
the threshold value is in MAP__ROBUST.

0 means natural weighting, which is optimal for point sources. The 
Robust weighting factor controls the resolution: better resolution is 
obtained for small values (at the expense of noise), resolution 
approaching the natural weighting scheme for large values.
Larger UV cell size give higher angular resolution (but again more noise).

MAP__ROBUST around .5 to 1 is a good compromise between noise increase
and angular resolution.

.ti -4
2 MAP__ROUNDING
.ti +4
  MAP__ROUNDING     Real 

Maximum error which can be tolerated between optimal size (
given by MAP__FIELD/MAP__CELL) and its rounded value MAP__SIZE
(as a power of 2^k 3^p 5^q) when rounding by floor (thus limiting
the field of view). If the rounding error becomes larger, rounding is
made by ceiling, which guarantees a larger field of view, but leads 
to bigger images.

Default is 0.05.  
  
.ti -4
2 MAP__SIZE

  MAP__SIZE[2]      Integer

Number of pixels in X and Y. It should preferentially be a power of two,
(although this is not strictly required) to speed-up the FFT. MAP__SIZE*MAP__CELL
should be at least twice the size of the field-of-view (primary beam size
for a single field). Enter 0,0 to let the command find a sensible map size.

MAP__SIZE is not used if MAP__FIELD is non zero.

Odd values are forbidden. 

Default is 0,0, i.e. UV__MAP will guess the most appropriate values
which depend on MAP__ROUNDING and MAP__POWER.


.ti -4
2 MAP__TAPEREXPO

  MAP__TAPEREXPO    Real

Taper exponent. The default is 2 (indicating a Gaussian) but smoother or
sharper functions can be used. 1 would give an Exponential, 4 would be getting
close to square profile...

.ti -4
2 MAP__TRUNCATE

  MAP__TRUNCATE    Real

Individual beam truncation level in PerCent.  Default value is 0. 
Current value can be overriden by option /TRUNCATE in commands UV__MAP.

.ti -4
2 MAP__UVTAPER

  MAP__UVTAPER[3]  Real

Parameters of the tapering function (Gaussian if MAP__TAPEREXPO = 2):
major axis at 1/e level [m], minor axis at 1/e level [m], and position angle [deg].

.ti -4
2 MAP__UVCELL

  MAP__UVCELL   Real

UV cell size for robust weighting [m].  Should be of the
order of half the dish diameter (7.5 m for NOEMA), or smaller or even larger.
It controls the beam shape in Robust weighting.

.ti -4
2 MAP__VERSION

  MAP__VERSION  Integer

[EXPERT Only] Code indicating which version of the UV__MAP and UV__RESTORE algorithm should
be used. 0 is optimal. -1 is the "historical" (pre-2016) version. 1 is an intermediate
version used during multi-frequency beams development.



.ti -4
2 Old__Names:

NAME is no longer used, and WEIGHT__MODE is obsolete.
.nf
MAP__RA          [  hours]  RA of map center
MAP__DEC         [    deg]  Dec of map center
MAP__ANGLE       [    deg]  Map position angle
MAP__SHIFT       [Yes/No ]  Shift phase center
.fi
are obsolete, superseded by MAP__CENTER. They are provided
only for compatibility with older scripts.

MAP__BEAM__STEP   is replaced by BEAM__STEP. An alias is
provided for compatibility reasons.

WCOL (the Weight channel) and MCOL[2] (the channel range) are
obsolete also. WCOL has no meaning when more than 1 beam must
be produced for all channels, and should be set to 0. 
MCOL is superseded by the /RANGE option facility. 

.nf
 NAME        [       ]  Label of the dirty image and beam plots
 UV__TAPER    [m,m,deg]  UV-apodization by convolution with a Gaussian
 WEIGHT__MODE [       ]  Weighting mode (NA|UN)
 UV__CELL     [m, ??  ]  UV cell size and threshold for Robust weighting
 MAP__FIELD   [ arcsec]  Map field of view
 MAP__CELL    [ arcsec]  Map cell size
 MAP__SIZE    [ pixels]  Map size in pixels (if MAP__FIELD is zero)
 MCOL        [       ]  First and Last channel to map
 WCOL        [       ]  Channel from which the weights are taken
 CONVOLUTION [       ]  Convolution function (5)
 UV__SHIFT    [       ]  Change the map phase center or map orientation?
 MAP__RA      [       ]  RA of map phase center
 MAP__DEC     [       ]  Dec of map phase center
 MAP__ANGLE   [    deg]  Map position angle
 MAP__BEAM__STEP   [       ]  Number of channels per synthesized beam plane
.fi

.ti -4
2 convolution

  Older variable name for MAP__CONVOLUTION

.ti -4
2 map__angle

  MAP__ANGLE      Real

Position Angle of the direction which will become the apparent North in the
map. Used only if MAP__SHIFT is YES.

Superseded by MAP__CENTER.

.ti -4
2 map__beam__step

  MAP__BEAM__STEP   Integher
  
  Older variable name for BEAM__STEP
  
.ti -4
2 map__dec

  MAP__DEC     Real

Dec of map center. Used only if MAP__SHIFT is YES.

Superseded by MAP__CENTER.

.ti -4
2 map__ra

  MAP__RA      Real

RA of map center. Used only if MAP__SHIFT is YES.

Superseded by MAP__CENTER.

.ti -4
2 mcol

  mcol[2]   Integer

[Deprecated] First and Last channel to image. Values of 0 mean imaging all the planes.
See UV__MAP /RANGE for a more flexible way to specify the channel range.

.ti -4
2 uv__cell

  Older variables for MAP__UVCELL (uv_cell[1]) and MAP__ROBUST

.ti -4
2 uv__shift

  Older variable name of MAP__SHIFT (this one is also obsolescent)

.ti -4
2 uv__taper

  Older variable name of MAP__UVTAPER

.ti -4
2 taper__expo

  Older variable name for MAP__TAPEREXPO

.ti -4
2 wcol

  WCOL      Integer

[Obsolescent] The channel from which the weight should be taken.  WCOL 
set to 0 means using a default channel. WCOL has no real meaning in all 
cases where more than one beam is computed for all channels.

.ti -4
2 weight__mode

  weight_mode      Character
  
[Deprecated] Weighting mode: Natural (optimum in terms of sensitivity) or robust
(usually lower sidelobes and higher spatial resolution) weighting.
This was needed in Mapping to toggle between Natural and Robust
weighting, while IMAGER does that based on MAP__ROBUST value.






