ARRGEN

ARRGEN is a program which generates two-dimensional arrays of interferometer telescopes and maps them onto the curved surface of a planet (e.g., the earth or the moon). The output is in the form of a STATIONS file containing the station name, radius, latitude, longitude, and zenith angle limit. (All telescopes are assumed to have an ALTAZ mount.) ARRGEN is useful for creating small arrays (such as VLA-like arrays, lunar arrays, etc.) for the purpose of running programs FAKE or HAZI.

Examples

1. Create User-Specified Array on Moon

% arrgen
  Radius     = 1738000
  LATitude   = 0:00:00
  LONgitud   = 0:00:00
  NSTAT      = 12
  EWoffset   =   0.0000,  452.7406, -498.3997,     403.3182, -208.2298,
              -402.4793, -454.2729,    0.55871205, 207.2576,  497.9849,
	       295.9012, -292.7386

  NSoffset   = 500.0000,  212.1913,   39.967656, -295.5227, 454.5767,
	      -296.6645,  208.8913, -499.9995,    455.0205,  44.839311, 
	      -403.0411, -405.3441
  OUTPUT     = "STATIONS"
  ARRNAMe    = "LUNAR"
  ZENANG     = 85.0
  /

2. Generate WYE Array on Moon

% arrgen
  Radius     = 1738000
  LATitude   = 0:00:00
  LONgitud   = 90:00:00 WEST
  NSTAT      = 12
  DIAMETER   = 1
  ROTATE     = -5
  OUTPUT     = "STATIONS"
  ARRNAMe    = "WYE"
  ZENANG     = 85.0
  ARRTYPe    = "WYE"
    ARRDIAM    = 1000
    EXPON      = 1.716
  XYPLOT
    PLOTFILE = wyearr.plt/ps
    LINEWIDTH=1
    DOTSIZE  =5
    MARK     =-1
  /

Parameters

Brackets [] indicate default values. End the list of parameters with a slash (/) or end-of-file (control-Z in VMS, control-D in Unix).

R = x                                   [ 637000 ]
LAT = dd:mm:ss                          [ 00:00:00 ]
LON = dd:mm:ss                          [ 00:00:00 ]
EAST, WEST                              [ EAST ]
NSTAT = n                               [ 2 ]
OUTPUT = "filename"                     [ "STATIONS" ]
ARRNAM = "arrayname"                    [ "ARRAY" ]
ZENANG = x                              [ 89.90 ]
ROT    = x                              [ 0.0 ]
ARRTYP = "arraytype"                    [ "SPECIFY" ]
  EW = x1,x2,x3,...                     [ compulsory if ARRTYP="SPECIFY" ]
  NS = y1,y2,y3,...                     [ compulsory if ARRTYP="SPECIFY" ]
  ARRDIAM = x                           [ -1 ]
  EXPON   = x                           [ 1.0 ]
  RINGORD = n                           [ 3, i.e., a WYE array ]
XYPLOT                                  [ default is no plot ]
  PLOTF  = "filename/plottype"          [ compulsory if XYPLOT is true ]
  DIAM   = x                            [ 0.0 ]
  MARK = n                              [ -1, i.e. a dot ]
  LINEW = n                             [ 1 ]
  FONT = n                              [ 1, i.e. a simple font ]
  DOTSIZE = n                           [ default is LINEWidth ]

Discussion

The primary purpose of ARRGEN is to produce STATIONS files for use in simulated interferometer observations. Station coordinates are specified in terms of the radius of the planet (earth, moon, etc.) on which the array is to be placed (the parameter R in meters), the latitude and longitude of the center of the array (LAT and LON in degrees), and the east-west and north-south offsets of each station. By default, the longitude values are assumed to be east longitude, but ARRGEN will interpret them as west longitude if the WEST parameter is specified.

The user has three choices of how to generate the coordinate offsets -- controlled by the parameter ARRTYP:

In addition, the entire array can be rotated about the vertical by ROT degrees west from north.

In the output STATIONS file there are NSTAT lines, and each station name is formed from the first 5 characters of the ARRNAM parameter. (In the first example above, the stations would be LUNAR-1, LUNAR-2, etc.) All telescopes are assumed to have an ALTAZ mount with the zenith angle limit given in degrees by ZENANG.

The algorithm for placing the telescopes on the planet surface lays out the array in a plane tangent to the point (R,LAT,LON) on the surface of the planet and then projects the telescopes radially down to the surface. (The infinite plane is mapped to a hemisphere centered at LAT and LON.) As such, ARRGEN is most useful for arrays which are small compared to the radius of the planet.

An XY plot of the stations can be created on the PGPLOT file given by PLOTF. The snapshot (u,v)-coverage for a source at the zenith is also plotted on the same page. The (u,v) positions are in meters and are computed after the stations are projected onto the planet's surface. Parameters affecting the plot are: the symbol used for plotting each (u,v) point (MARK), the width of the border and other lines (LINEWidth), the FONT used (1=simple, 2=roman, 3=italic, 4=script), and the pen size for the drawing symbols (DOTSIZE). To test the consistency of the telescope spacing, the user can specify the DIAMeter of each telescope, resulting in appropriately-scaled circles at the position of each array element in the XY plot.

History

Version 1.0: 1990 Sep 25. New program (D. L. Meier).
Version 1.1: 1990 Nov 21. Add XYPLOT of station positions.
Version 1.2: 1990 Dec 6. Add computation of standard Wye arrays.
Version 1.3: 1990 Dec 14. Add computation of standard crystalline (Cornwell) ring arrays. Fix plot bugs and add snapshot UV coverage plot.
Version 1.4: 1991 Mar 18. Convert lat/long from decimal degrees to decimal arcseconds (a la KEYIN).
Version 1.5: 1993 Jan 5. Divide XYPLOT into XYPLOT and UVPLOT (DLM).
Version 1.6: 1993 Jul 15. Use PGPLOT routine PGCIRC (TJP).
Version 1.7: 1993 Nov 11. Modified to conform to Fortran-77 (TJP).


Tim Pearson, California Institute of Technology
tjp·astro.caltech.edu