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3 michaesp 1
c      *************************************************************
2
c      * This package provides a general interpolaton routine      *
3
c      *************************************************************	
4
 
5
c     The main interface routines are:
6
c         get_index3,4 : get the grid indices for interpolation
7
c         int_index3,4 : interpolate to the grid position
8
 
9
c     -------------------------------------------------------------
10
c     Get index in grid space for interpolation
11
c     -------------------------------------------------------------
12
 
13
      subroutine get_index4 (rid,rjd,rkd,xpo,ypo,ppo,rtp,
14
     >                       vert0,vert1,surf0,surf1,mode,
15
     >                       nx,ny,nz,lonw,lats,dlon,dlat,misdat)
16
 
17
c     Purpose:
18
c        This subroutine determines the indices (rid,rjd,rkd) in grid 
19
c        space for a point in physical space (xpo,ypo,ppo). The 
20
c        horizontal grid is specified by the south-west point (lats,lonw)
21
c        and the grid spacing (dlat,dlon). The vertical grid is given
22
c        by <vert(n1,n2,n3)>. The lower boundary (typicall surface 
23
c        pressure) is given by <surf(n1,n2)>.
24
c     Arguments:
25
c        rid,rjd,rkd  real  output   grid location to be interpolated to
26
c        xpo,ypo,ppo  real  input    physical coordinates
27
c        rtp          real  input    relative time position (0=beginning, 1=end)
28
c        n1,n2,n3     int   input    grid dimensions in x-, y- and p-direction
29
c        lats,lonw    real  input    south and west boundary of grid space
30
c        vert         real  input    vertical coordinate grid
31
c        surf         real  input    lower boundary (surface pressure)
32
c        mode         int   input    direction of vertical axis (p=1,th=-1)
33
c                                        1: linear, 1 -> nz (th)
34
c                                        2: linear, nz -> 1 (pv)
35
c                                        3: binary (p)
36
 
37
      implicit none
38
 
39
c     Declartion of function parameters
40
      integer   nx,ny,nz
41
      real      xpo,ypo,ppo,rtp
42
      real      vert0(nx*ny*nz),vert1(nx*ny*nz)
43
      real      surf0(nx*ny)   ,surf1(nx*ny*nz)
44
      real      rid,rjd,rkd
45
      real      dlat,dlon,lats,lonw
46
      real      misdat
47
      integer   mode
48
 
49
c     Set numerical parameters
50
      real      eps
51
      parameter (eps=1.e-8)
52
 
53
c     Auxiliary variables
54
      real      rid0,rjd0,rkd0,rid1,rjd1,rkd1
55
      integer   i
56
 
57
c     Externals 
58
      real      int_time
59
      external  int_time
60
 
61
c     Get the inidices
62
      if (abs(rtp).lt.eps) then
63
         call  get_index3 (rid,rjd,rkd,xpo,ypo,ppo,mode,
64
     >                     vert0,surf0,nx,ny,nz,lonw,lats,dlon,dlat)
65
      elseif (abs(rtp-1.).lt.eps) then
66
         call  get_index3 (rid,rjd,rkd,xpo,ypo,ppo,mode,
67
     >                     vert1,surf1,nx,ny,nz,lonw,lats,dlon,dlat)
68
      else
69
         call  get_index3 (rid0,rjd0,rkd0,xpo,ypo,ppo,mode,
70
     >                     vert0,surf0,nx,ny,nz,lonw,lats,dlon,dlat)
71
         call  get_index3 (rid1,rjd1,rkd1,xpo,ypo,ppo,mode,
72
     >                     vert1,surf1,nx,ny,nz,lonw,lats,dlon,dlat)
73
         rid = int_time (rid0,rid1,rtp,misdat)
74
         rjd = int_time (rjd0,rjd1,rtp,misdat)
75
         rkd = int_time (rkd0,rkd1,rtp,misdat)
76
 
77
      endif
78
 
79
      end
80
 
81
c     -------------------------------------------------------------
82
c     Interpolate to an arbitrary position in grid space and time
83
c     -------------------------------------------------------------
84
 
85
      real function int_index4 (ar0,ar1,n1,n2,n3,rid,rjd,rkd,rtp,misdat)
86
 
87
c     Purpose:
88
c        This subroutine interpolates a 3d-array to an arbitrary
89
c        location within the grid including a linear time-interpolation. 
90
c     Arguments:
91
c        rid,rjd,rkd  real  output   grid location to be interpolated to
92
c        xpo,ypo,ppo  real  input    physical coordinates
93
c        n1,n2,n3     int   input    grid dimensions in x-, y- and p-direction
94
c        lats,lonw    real  input    south and west boundary of grid space
95
c        vert         real  input    vertical coordinate grid
96
c        surf         real  input    lower boundary (surface pressure)
97
 
98
      implicit none
99
 
100
c     Declartion of function parameters
101
      integer   n1,n2,n3
102
      real      ar0(n1*n2*n3),ar1(n1*n2*n3)
103
      real      rid,rjd,rkd
104
      real      rtp
105
      real      misdat
106
 
107
c     Set numerical parameters
108
      real      eps
109
      parameter (eps=1.e-8)
110
 
111
c     Externals  
112
      real      int_index3,int_time
113
      external  int_index3,int_time
114
 
115
c     Auxiliary variables
116
      real      val0,val1,val
117
 
118
c     Do the 3d-interpolation
119
      if (abs(rtp).lt.eps) then
120
         val = int_index3 (ar0,n1,n2,n3,rid,rjd,rkd,misdat)
121
      elseif (abs(rtp-1.).lt.eps) then
122
         val = int_index3 (ar1,n1,n2,n3,rid,rjd,rkd,misdat)
123
      else
124
         val0 = int_index3 (ar0,n1,n2,n3,rid,rjd,rkd,misdat)
125
         val1 = int_index3 (ar1,n1,n2,n3,rid,rjd,rkd,misdat)
126
         val  = int_time (val0,val1,rtp,misdat)
127
      endif
128
 
129
c     Return value
130
      int_index4 = val
131
 
132
      return
133
      end
134
 
135
 
136
c     -------------------------------------------------------------
137
c     Interpolate to an arbitrary position in grid space
138
c     -------------------------------------------------------------
139
 
140
      real function int_index3 (ar,n1,n2,n3,rid,rjd,rkd,misdat)
141
 
142
c     Purpose:
143
c        This subroutine interpolates a 3d-array to an arbitrary
144
c        location within the grid. The interpolation includes the 
145
c        testing of the missing data flag 'misdat'. If one dimension
146
c        is 1, a 2d-interpolation is performed; if two dimensions
147
c        are 1, it is a 1d-interpolation; if all three dimensions are
148
c        1, no interpolation is performed and the input value is
149
c        returned.
150
c     Arguments:
151
c        ar        real  input   input data array
152
c        n1,n2,n3  int   input   dimensions of ar
153
c        ri,rj,rk  real  input   grid location to be interpolated to
154
c        misdat    real  input   missing data flag (on if misdat<>0)
155
 
156
      implicit none
157
 
158
c     Declartion of function parameters 
159
      integer   n1,n2,n3
160
      real      ar(n1*n2*n3)
161
      real      rid,rjd,rkd
162
      real      misdat
163
 
164
c     Set numerical parameters
165
      real      eps
166
      parameter (eps=1.e-8)
167
 
168
c     Local variables
169
      integer   i,j,k,ip1,jp1,kp1
170
      real      frac0i,frac0j,frac0k,frac1i,frac1j,frac1k
171
      real      ri,rj,rk
172
      real      val000,val001,val010,val011,val100,val101,val110,val111
173
      real      frc000,frc001,frc010,frc011,frc100,frc101,frc110,frc111
174
      real      frc
175
      real      mdv
176
      real      val
177
 
178
c     Elementary test for dimensions
179
      if ( (n1.lt.1).or.(n2.lt.1).or.(n3.lt.1) ) then
180
         print*,'Invalid grid dimensions ',n1,n2,n3
181
         stop
182
      endif
183
 
184
c     Activate or inactive the missing data check (quick and dirty)
185
      if (misdat.ne.0.) then
186
         mdv = misdat
187
      else
188
         mdv = 257.22725394015
189
      endif
190
 
191
c     Bring the indices into the grid space
192
      ri = amax1(1.,amin1(float(n1),rid))
193
      rj = amax1(1.,amin1(float(n2),rjd))
194
      rk = amax1(1.,amin1(float(n3),rkd))
195
 
196
c     Get the index of the west-south-bottom corner of the box
197
      i   = min0(int(ri),n1-1)
198
      ip1 = i+1
199
      j   = min0(int(rj),n2-1)
200
      jp1 = j+1
201
      k   = min0(int(rk),n3-1)
202
      kp1 = k+1
203
 
204
c     Special handling for 2d arrays
205
      if (n3.eq.1) then
206
         k=1
207
         kp1=1
208
      endif
209
 
210
c     Get location relative to grid box
211
      if ( i.ne.ip1 ) then
212
         frac0i = ri-float(i)
213
         frac1i = 1.-frac0i
214
      else
215
         frac0i = 0.
216
         frac1i = 1.
217
      endif
218
      if ( j.ne.jp1 ) then
219
         frac0j = rj-float(j)
220
         frac1j = 1.-frac0j
221
      else
222
         frac0j = 0.
223
         frac1j = 1.
224
      endif
225
      if ( k.ne.kp1 ) then
226
         frac0k = rk-float(k)
227
         frac1k = 1.-frac0k
228
      else
229
         frac0k = 0.
230
         frac1k = 1.
231
      endif
232
 
233
c     On a grid point - take the grid point value 
234
      if ( ( abs(frac0i).lt.eps ).and.
235
     >     ( abs(frac0j).lt.eps ).and.
236
     >     ( abs(frac0k).lt.eps ) ) then
237
 
238
         val = ar( i + n1*(j -1) + n1*n2*(k -1) )
239
         goto 100
240
 
241
      endif
242
 
243
c     Init the fractions
244
      frc000 = frac1i * frac1j * frac1k
245
      frc001 = frac0i * frac1j * frac1k
246
      frc010 = frac1i * frac0j * frac1k
247
      frc011 = frac0i * frac0j * frac1k
248
      frc100 = frac1i * frac1j * frac0k
249
      frc101 = frac0i * frac1j * frac0k
250
      frc110 = frac1i * frac0j * frac0k
251
      frc111 = frac0i * frac0j * frac0k
252
 
253
c     Init the values
254
      val000 = ar( i   + n1*(j  -1) + n1*n2*(k  -1) )
255
      val001 = ar( ip1 + n1*(j  -1) + n1*n2*(k  -1) )
256
      val010 = ar( i   + n1*(jp1-1) + n1*n2*(k  -1) )
257
      val011 = ar( ip1 + n1*(jp1-1) + n1*n2*(k  -1) )
258
      val100 = ar( i   + n1*(j  -1) + n1*n2*(kp1-1) )
259
      val101 = ar( ip1 + n1*(j  -1) + n1*n2*(kp1-1) )
260
      val110 = ar( i   + n1*(jp1-1) + n1*n2*(kp1-1) )
261
      val111 = ar( ip1 + n1*(jp1-1) + n1*n2*(kp1-1) )
262
 
263
c     Handle missing data
264
      if ( abs(val000-mdv).lt.eps ) frc000 = 0.
265
      if ( abs(val001-mdv).lt.eps ) frc001 = 0.
266
      if ( abs(val010-mdv).lt.eps ) frc010 = 0.
267
      if ( abs(val011-mdv).lt.eps ) frc011 = 0.
268
      if ( abs(val100-mdv).lt.eps ) frc100 = 0.
269
      if ( abs(val101-mdv).lt.eps ) frc101 = 0.
270
      if ( abs(val110-mdv).lt.eps ) frc110 = 0.
271
      if ( abs(val111-mdv).lt.eps ) frc111 = 0.
272
 
273
c     Build the final value
274
      frc = frc000 + frc001 + frc010 + frc011 + 
275
     >      frc100 + frc101 + frc110 + frc111   
276
      if ( frc.gt.0. ) then
277
         val = 1./frc * ( frc000 * val000 + frc001 * val001 +
278
     >                    frc010 * val010 + frc011 * val011 +
279
     >                    frc100 * val100 + frc101 * val101 +
280
     >                    frc110 * val110 + frc111 * val111 )
281
      else
282
         val = misdat
283
      endif
284
 
285
c     Return the value 
286
 100  continue
287
 
288
      int_index3 = val
289
 
290
      end
291
 
292
 
293
c     -------------------------------------------------------------
294
c     Time interpolation
295
c     -------------------------------------------------------------
296
 
297
      real function int_time (val0,val1,reltpos,misdat)
298
 
299
c     Purpose:
300
c        This subroutine interpolates linearly in time between two
301
c        values.
302
c     Arguments:
303
c        val0      real  input   value at time 0
304
c        val1      real  input   value at time 1
305
c        reltpos   real  input   relative time (between 0 and 1)
306
c        misdat    real  input   missing data flag (on if misdat<>0)
307
 
308
      implicit none
309
 
310
c     Declaration of parameters
311
      real      val0
312
      real      val1
313
      real      reltpos
314
      real      misdat
315
 
316
c     Numerical epsilon
317
      real      eps
318
      parameter (eps=1.e-8)
319
 
320
c     Local variables
321
      real      val
322
      real      mdv
323
 
324
c     Activate or inactive the missing data check (quick and dirty)
325
      if (misdat.ne.0.) then
326
         mdv = misdat
327
      else
328
         mdv = 257.22725394015
329
      endif
330
 
331
c     Do the linear interpolation
332
      if ( abs(reltpos).lt.eps ) then
333
         val = val0
334
      elseif ( abs(reltpos-1.).lt.eps ) then
335
         val = val1
336
      elseif ( (abs(val0-mdv).gt.eps).and.
337
     >         (abs(val1-mdv).gt.eps) ) then
338
         val = (1.-reltpos)*val0+reltpos*val1
339
      else
340
         val = mdv
341
      endif
342
 
343
c     Return value
344
      int_time = val
345
 
346
      end
347
 
348
 
349
c     -------------------------------------------------------------
350
c     Get the position of a physical point in grid space
351
c     -------------------------------------------------------------
352
 
353
      subroutine get_index3 (rid,rjd,rkd,xpo,ypo,ppo,mode,
354
     >                       vert,surf,nx,ny,nz,lonw,lats,dlon,dlat)
355
 
356
c     Purpose:
357
c        This subroutine determines the indices (rid,rjd,rkd) in grid 
358
c        space for a point in physical space (xpo,ypo,ppo). The 
359
c        horizontal grid is specified by the south-west point (lats,lonw)
360
c        and the grid spacing (dlat,dlon). The vertical grid is given
361
c        by <vert(n1,n2,n3)>. The lower boundary (typicall surface 
362
c        pressure) is given by <surf(n1,n2)>.
363
c     Arguments:
364
c        rid,rjd,rkd  real  output   grid location to be interpolated to
365
c        xpo,ypo,ppo  real  input    physical coordinates
366
c        n1,n2,n3     int   input    grid dimensions in x-, y- and p-direction
367
c        lats,lonw    real  input    south and west boundary of grid space
368
c        vert         real  input    vertical coordinate grid
369
c        surf         real  input    lower boundary (surface pressure)
370
c        mode         int   input    direction of vertical axis 
371
c                                        1: linear, 1 -> nz (th)
372
c                                        2: linear, nz -> 1 (pv)
373
c                                        3: binary (p)
374
 
375
 
376
      implicit none
377
 
378
c     Declartion of function parameters
379
      integer   nx,ny,nz
380
      real      vert(nx*ny*nz)
381
      real      surf(nx*ny)
382
      real      rid,rjd,rkd
383
      real      xpo,ypo,ppo
384
      real      dlat,dlon,lats,lonw
385
      integer   mode
386
 
387
c     Numerical epsilon
388
      real      eps
389
      parameter (eps=1.e-8)
390
 
391
c     Local variables
392
      integer   i,j,k
393
      real      ppo0,ppo1,ppom,psur
394
      integer   i0,im,i1
395
 
396
c     Externals 
397
      real      int_index3
398
      external  int_index3
399
 
400
c     Get the horizontal grid indices
401
      rid=(xpo-lonw)/dlon+1.
402
      rjd=(ypo-lats)/dlat+1.
403
 
404
c     Two-dimensional interpolation on horizontal plane: return
405
      if ( nz.eq.1 ) then
406
         rkd = 1.
407
         goto 100
408
      endif
409
 
410
c     Lowest-level interpolation: return
411
      if ( abs(ppo-1050.).lt.eps ) then
412
         rkd = 1.
413
         goto 100
414
      endif
415
 
416
c     Get the pressure at the lowest level and at the surface
417
      ppo0 = int_index3(vert,nx,ny,nz,rid,rjd,real(1),0.)
418
      psur = int_index3(surf,nx,ny, 1,rid,rjd,real(1),0.)
419
 
420
c     Decide whether the pressure is ascending or descending
421
      ppo1 = int_index3(vert,nx,ny,nz,rid,rjd,real(nz),0.)
422
      if ( ppo1.gt.ppo0 ) then
423
         ppo0 = ppo1
424
      endif
425
 
426
c     The point is between the surface and the lowest level: return
427
      if ( mode.eq.3 ) then
428
        if ( (ppo.ge.ppo0).and.(ppo.le.psur).or.
429
     >       (ppo.le.ppo0).and.(ppo.ge.psur) )
430
     >  then
431
           psur = int_index3(surf,nx,ny, 1,rid,rjd,real(1),0.)
432
           rkd  = (psur-ppo)/(psur-ppo0)
433
           goto 100
434
        endif
435
      endif
436
 
437
c     Full-level search (TH): linear ascending scanning through all levels
438
      if ( mode.eq.1 ) then
439
 
440
         ppo0 = int_index3(vert,nx,ny,nz,rid,rjd,real(1),0.)
441
         rkd=0
442
         do i=1,nz-1
443
            ppo1 = int_index3(vert,nx,ny,nz,rid,rjd,real(i+1),0.)
444
            if ( (ppo.gt.ppo0).and.(ppo.le.ppo1) ) then
445
               rkd=real(i)+(ppo-ppo0)/(ppo1-ppo0)
446
               goto 100
447
            endif
448
            ppo0 = ppo1
449
         enddo
450
 
451
c     Full-level search (PV): linear descending scanning through all levels
452
      elseif ( mode.eq.2 ) then
453
 
454
         ppo1 = int_index3(vert,nx,ny,nz,rid,rjd,real(nz),0.)
455
         rkd=0
456
         do i=nz-1,1,-1
457
            ppo0 = int_index3(vert,nx,ny,nz,rid,rjd,real(i),0.)
458
            if ( (ppo1.gt.ppo).and.(ppo0.le.ppo) ) then
459
               rkd=real(i)+(ppo0-ppo)/(ppo0-ppo1)
460
               goto 100
461
            endif
462
            ppo1 = ppo0
463
         enddo
464
 
465
c     Full-level search (P):  binary search 
466
      elseif ( mode.eq.3 ) then
467
 
468
         rkd  = 0
469
         i0   = 1
470
         i1   = nz
471
         ppo0 = int_index3(vert,nx,ny,nz,rid,rjd,real( 1),0.)
472
         ppo1 = int_index3(vert,nx,ny,nz,rid,rjd,real(nz),0.)
473
 
474
         do while ( i1.gt.(i0+1) )
475
            im   = (i0+i1)/2
476
            ppom = int_index3(vert,nx,ny,nz,rid,rjd,real(im),0.)
477
            if (ppom.lt.ppo) then
478
               i1   = im
479
               ppo1 = ppom
480
            else
481
               i0   = im
482
               ppo0 = ppom
483
            endif
484
         enddo
485
 
486
         rkd=real(i0)+(ppo0-ppo)/(ppo0-ppo1)
487
 
488
      endif
489
 
490
c     Exit point for subroutine
491
 100  continue
492
 
493
      end
494