[WP] (issue7_refract): define upper limit for single precision values

src/ts/refract/sub/refract_settracevp.f

@@ -50,6 +50,8 @@ c defined in refract_seipar.inc
 c 
       integer i
       logical reverse
+      real limit
+      parameter(limit=1.e38)
 c
       include 'refract_dim.inc'
       include 'refract_data.inc'
@@ -59,6 +61,20 @@ c
 cE
 c
 c ----------------------------------------------------------------------
+c limit
+c -----
+c
+c To prevent numerical overflow, we must set an upper limit for floating
+c point single precision variables. Fortran 95 provides a function
+c huge(), where
+c
+c   huge(1.0)=3.40282347E+38
+c
+c in a standard Intel environment with gfortran. Since this function
+c might not be available for users relying on the code being compiled
+c with a standard Fortran 77 compiler, I set the limit to 1.e38
+c
+c ----------------------------------------------------------------------
 c 
 c tov stands for total viewport
 c trv stands for trace viewport
@@ -143,29 +159,60 @@ c    coordinates in counts.
 c ----------------------------------------------------------- 
 c
 c factor "world coordinates -> normalized device coordinates"
+c derived from the total viewport
       vppm=(tov_vptop-tov_vpbot)/(tov_rmax-tov_rmin)
 c 
 c result will be true in case we expect any part of the curve to be visible
 c within the trace viewport
       result=.true.
 c
-c get clipping region in terms of the total viewports world coordinates
+c a) Calculate raw offset range
+c -----------------------------
+c
+c The offset range to be used for display of this trace is defined by
+c the clipping margin to larger and smaller offsets, centred on the
+c trace's offset.
+c
+c Calculate the raw offset range to be used, simplay based on trace's
+c offset and clipping level:
       trv_rtop=roffset(i)+plpar_clip
       trv_rbot=roffset(i)-plpar_clip
 c
+c Check if this - maybe - already is outside global plot range
+c
 c will there anything be visible
       if ((trv_rtop.lt.tov_rmin).or.(trv_rbot.gt.tov_rmax))
      &  result=.false.
 c 
       if (result) then
 c 
+c b) Adjust offset range
+c ----------------------
+c
+c The offset range defined by the clipping margin might partly be
+c outside the global offset range.
+c
 c respect clipping by total viewport
         trv_rtop=min(trv_rtop, tov_rmax)
         trv_rbot=max(trv_rbot, tov_rmin)
 c
+c trv_rtop and trv_rtop now specify the actual offset range in the
+c window of the total graphical viewport to be used for the display of
+c the current trace. If any sample value should fall outside this offset
+c range, they shall now be displayed.
+c
+c c) Find corresponding viewport in device coordinates
+c ----------------------------------------------------
+c
+c To select a plot area on the device surface, we have to use normalized
+c device coordinates. 
+c
 c map to a viewport range
         trv_vpbot=(trv_rbot-tov_rmin)*vppm+tov_vpbot
         trv_vptop=(trv_rtop-tov_rmin)*vppm+tov_vpbot
+c
+c d) Find world coordinates for traces viewport in counts
+c -------------------------------------------------------
 c 
 c remap equivalent offset to seismogram counts
         if (reverse) then