OPEN-MAP-FILE

Open an existing map file, or create a new one. Note that the file title and file owner strings are for your information only, and have no wider significance.

Until further notice, maps should contain an odd number of pixels in both coordinates so that the map center corresponds to a measured data point. The position angle is measured in degrees E of N (i.e.standard astronomical convention), and will normally be chosen to match that of the actual observation grid, although it need not necessarily do so.

If the RA and Dec are specified when the map is created these will define the map centre; otherwise the RA and Dec of the ``map centre'' of the first scan added to the map will be used.

In V6.2, you will now be asked also for the number of spectral channels. This is partly to simplify the code, which previously delayed asking for virtual memory until you added the first spectrum, but also to `remind' you how much memory you might require. SPECX may require a total of 3 cubes to reside in virtual memory at once -- the original raw cube (which is maintained during ADD-TO-MAP, DELETE-FROM-MAP etc); the interpolated or rotated cube used for display purposes; and at times a third cube when the previously rotated or interpolated cube is being interpolated or rotated. If the total memory required by these cubes significantly exceeds the working set size these commands will lead to a huge amount of paging, and can essentially halt the system.

Your use of virtual memory can be reduced significantly by:

• Reducing the number of spectral channels by deleting them from the ends of the array with TRUNCATE or DROP-CHANNELS .
• Binning adjacent channels where the velocity resolution required is less than that afforded by the backend (use BIN-SPECTRUM.)
• Making the map as small as possible.

Relevant flags:

*CUBE_LOADED	L4	A map is open and data cube loaded into memory.
join-the-dots otherwise.
*CUBE_SIZE	I4	Memory requirement for each cube, in bytes.

Examples:

    >> open-map-file<CR>
    File name? (extension will be .MAP) [    l483_test] l483core<CR>

    Inquiring about file: l483core.MAP
    File already exists - Opening it.

    Map file l483core.MAP opened on unit 119
    Map version number:    2.000000    
          39780 bytes required for data cube
             72 spectra from current map file read into data cube

    ..


    >> open-map-file<CR>
    File name? (extension will be .MAP) [    l483core] test<CR>
 
    Inquiring about file: test.MAP
    File does not exist - Creating it now...
    Map file opened on unit          119
    File title? test<CR>
    File owner? rachael<CR>
    RA of map centre (<CR> for auto)? '05 32 24.7'<CR>
    Dec. of map centre? '-05 24 30'<CR>
    x (R.A.) & y (Dec) cell sizes? (arcsec) [ 24.7   0.0] 10 10<CR>
    Position angle of map y-axis? (degrees) [  30.0] <CR>
    Maximum number of cells on x & y axes? [ 17   9] <CR>
    Number of spectral channels? [65] <CR>
    ..