pro tic_one, min, pixx, incr, min2, tic1, RA=ra ;+ ; NAME: ; TIC_ONE ; PURPOSE: ; Determine the position of the first tic mark for astronomical images. ; EXPLANATION: ; For use in labelling images with right ascension ; and declination axes. This routine determines the ; position in pixels of the first tic. ; ; CALLING SEQUENCE: ; tic_one, zmin, pixx, incr, min2, tic1, [RA = ] ; ; INPUTS: ; zmin - astronomical coordinate value at axis zero point (degrees ; or hours) ; pixx - distance in pixels between tic marks (usually obtained from TICS) ; incr - increment in minutes for labels (usually an even number obtained ; from the procedure TICS) ; ; OUTPUTS: ; min2 - astronomical coordinate value at first tic mark ; tic1 - position in pixels of first tic mark ; ; EXAMPLE: ; Suppose a declination axis has a value of 30.2345 degrees at its ; zero point. A tic mark is desired every 10 arc minutes, which ; corresponds to 12.74 pixels. Then ; ; IDL> TIC_ONE, 30.2345, 12.74, 10, min2, tic1 ; ; yields values of min2 = 30.333 and tic1 = 7.55, i.e. the first tic ; mark should be labeled 30 deg 20 minutes and be placed at pixel value ; 7.55 ; ; REVISION HISTORY: ; by B. Pfarr, 4/15/87 ; Corrected documentation example W. Landsman Mar 2017 ;- On_error,2 ; convert min to minutes if keyword_set(RA) then mul = 4.0000 else mul = 60.00000 min1 = min*mul ;Convert from degrees to minutes ; incra = abs(incr) rem = min1 mod incra ;get remainder sign = min1*incr if ( sign GT 0 ) then begin tic1 = pixx - abs(rem)*(pixx/incra) min2 = (min1+incr-rem)/mul endif else begin tic1 = abs(rem)*(pixx/incra) min2 = (min1 - rem)/mul endelse return end