PHOT(OM) - Simple statistics and profile utilities

Packages commonly used interactions with the image currently displayed on the LEXIDATA. The program has several modes of operation which are described briefly below. The user interaction is performed entirely with the Lexidata trackerball/joystick and switches. (Each switch has a specific meaning which is common to all the Lexidata programs - details are in the next section).

There are six modes of operation, and the MODE switch is used to cycle through them. The initial mode is ``Profile'', followed by ``Stats'', ``List'', ``Zoom'', ``Cursor'', and ``Dist'' respectively. The RESET switch unzooms the image only when in ZOOM mode and then resets everything back to its default value. The EXIT switch always causes immediate program exit.

The behaviour of the remaining switches, READ, DOWN, UP, is described for each mode : -

PROFILE - The read switch causes a Profile to be drawn from the previous cursor position to the current position. Currently only horizontal and vertical profiles are permitted. The UP and down switches control scaling - DOWN halves the cutoff, UP doubles it.
STATS - The READ switch causes statistics of a rectangular neighbourhood of the current position to be listed on the terminal. These include a sky estimate based on the rim of the box, estimate of sky subtracted flux, standard deviations and maximum/minimum pixel values within the box. The UP and DOWN switches control the box size - initially it is of side 21 and DOWN decreases it by 2, UP increases it by 2. Two passes are made through the data so that sources in the rim can be clipped out before estimating the sky background and noise. The level of clipping is controlled by CLIPSIG (default is 2.0). The width of the rim is controlled by RIMWIDTH (default is 10) and the number of above the noise for a believable source by NUMSIG (default is 10.0). The defaults can be changed if required as shown below.
Examples
Adam:> PHOT RIMWIDTH = 10 CLIPSIG = 3.0 NUMSIG = 3.0
LIST - The READ switch causes the pixel values of a rectangular neighbourhood to be listed on the terminal. The box is the same one as used by STATS and its size is controlled in the same way using the UP and DOWN switches.
ZOOM - The READ switch causes the image to be zoomed about the current position with the current zoom factor. The UP and DOWN switches control the current ZOOM factor - initially it is whatever it was on entry to PHOTOM and DOWN decreases it by 1, UP increases it by 1.
CURSOR - The READ switch merely echoes the current position in pixel and user coordinates, plus the corresponding data value. In fact this information is given in all modes. The UP and DOWN switches control the box size in the same way as the STATS and LIST switches.
DIST - The READ switch causes the distance between the current position and the last position to be calculated (in pixels) and listed on the terminal. The UP and DOWN switches control the box size in the same way as the STATS and LIST switches.

Parameters

There are some, but they should not normally be necessary when running within the CCD system.

Examples

Adam:> PHOTOM

Notes

PHOTOM, in common with all the Lexidata programs, will automatically use the current image, i.e. the one that has been most recently displayed from the CCD.

PHOTOM uses the BIAS value given at startup when it estimates line centres. A better value can be estimated using PHOTOM in STATS mode or else the STATS facility. BIAS in as ACL variable so can be updated by typing BIAS=< newbias >, or run the procedure BIAS and answer the prompt - this has the advantage of giving the current bias first.

The pixel coordinates of the last two points selected in PHOTOM are written as ACL variables PHOTOM_PXX1, PHOTOM_PXY1, PHOTOM_PXX2 and PHOTOM_PXY2. Thus PHOTOM can be used in a procedure as an easy way of getting two points selected by the user.

Fri Jun 10 17:31:56 BST 1994