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20001228: Sat projection earth radius
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- Subject: 20001228: Sat projection earth radius
- Date: Thu, 28 Dec 2000 10:41:45 -0700
------- Forwarded Message
>To: address@hidden,
>To: address@hidden (Justin Sharp),
>To: address@hidden (Harry Edmon)
>From: David Ovens <address@hidden>
>Subject: I found and fixed a bug in GEMPAK imar2gm.f
>Organization: UCAR/Unidata
>Keywords: 200012281724.eBSHOMo09342
To: address@hidden
Justin Sharp, U.W. (address@hidden)
Harry Edmon, U.W. (address@hidden)
Hello,
I've been attempting to modify Justin Sharp's excellent program that
makes McIdas area files out of 30-second terrain data. (A program that
he has placed on CD with the terrain data set). It has always worked
fine with the RECTilinear projection of McIdas, but when I tried to
use IMGREMAP as in the following code extract
$imgremap = "imgremap.k MYDATA/IMAGES.$area MYDATA/IMAGES.9998 PRO=MERC
LATLON=$center_lat $center_lon RES=1 SIZE=ALL";
I was having trouble with the GEMPAK map being offset with the
terrain. In McIdas, however, I could not discern any problem with the
remapped file.
Well, I have gone to the McIdas source and to the GEMPAK source and I
have been able to fix the problem in GEMPAK-5.6.A by correcting a
discrepancy between the Earth radius used in GEMPAK and that used in
the McIdas file. I have modified $GEMPAK/source/gemlib/im/imar2gm.f
as you will see below to replace RADIUS with re (obtained from the
navigation header of the file).
I have tested this with MERC, LAMB, and PS terrain/McIdas files and it
all seems to line up fine using sfmap. I am also considering an
optional projection "PROJ = sat2mer" that would remap a satellite file
of any projection to a Mercator projection inside GEMPAK. I'll let
you know if I ever get around to doing this....
David
========================= imar2gm.f ====================
SUBROUTINE IM_AR2GM ( imgfil, rnvblk, iret )
C************************************************************************
C* IM_AR2GM *
C* *
C* This subroutine reads the header information from a MCIDAS AREA file *
C* and sets the navigation *
C* *
C* IM_AR2GM ( IMGFIL, RNVBLK, IRET ) *
C* *
C* Input parameters: *
C* IMGFIL CHAR* Image file *
C* *
C* Output parameters: *
C* RNVBLK (LLNNAV) REAL Navigation block *
C* IRET INTEGER Return code *
C* 0 = normal return *
C* -2 = Error opening/reading file*
C* -3 = Invalid image file format *
C* -4 = Invalid image file header *
C* -5 = Invalid image navigation *
C** *
C* Log: *
C* J. Cowie/COMET 2/95 *
C* C. Lin/EAI 6/95 Change input from file name to lunmf *
C* Change GG_* to IM_* for projection setup*
C* J. Cowie/COMET 10/95 Set xy image scaling to 1.0 *
C* J. Cowie/COMET 4/96 Add calibration type, check for 'RAW ' *
C* T. Lee/GSC 7/96 Renamed IM_ARHD; Cleaned up & eliminated*
C* map projection calls *
C* D. Keiser/GSC 8/96 Added RETURN after call to GSATMG *
C* T. Lee/GSC 9/96 Used RADIUS and floating point *
C* D.W.Plummer/NCEP 10/96 Fix RADR processing bug, rem to RADIUS *
C* T. Lee/GSC 11/96 Declared timfil; Used meter everywhere *
C* J. Cowie/COMET 1/97 Changed IMGDEF common variables names *
C* S. Chiswell/UNIDATA 1/97 Add extra scaling chck for RECT images *
C* J. Cowie/COMET 2/97 Fixed RADR off-by-one error *
C* J. Cowie/COMET 12/97 Changed jyear to 1900 + current year *
C* J. Cowie/COMET 12/97 Added imradf, removed immode, imraw *
C* S. Danz/AWC 05/99 Fix to RECT off-by-one error *
C* S. Jacobs/NCEP 6/00 Used correct image name in GSATMG call *
C* Chiz/Unidata 7/00 Added swap test initialization and *
C* im_calib call if calibration exists *
C* S. Danz/AWC 10/00 Fix RECT setting center longitude *
C* D. Ovens/UW 12/00 Fix MERC,LAMB,PS Earth Radius mismatches*
C************************************************************************
INCLUDE 'GEMPRM.PRM'
INCLUDE 'IMGDEF.CMN'
INCLUDE 'AREAFL.CMN'
C*
CHARACTER*(*) imgfil
REAL rnvblk (*)
C*
CHARACTER navtyp*4, proj*3
INTEGER iarray (704), idtarr (3)
C*
EQUIVALENCE (iarray (1), iadir (1))
EQUIVALENCE (iarray (65), ianav (1))
C------------------------------------------------------------------------
iret = 0
sign = 1.
C
C* Open the file and read AREA DIR and NAV blocks
C
CALL FL_DOPN ( imgfil, 704, .false., lunmf, iret )
CALL FL_READ ( lunmf, 1, 704, iarray, ier )
IF ( ier .ne. 0 ) THEN
iret = -1
RETURN
END IF
CALL FL_CLOS ( lunmf, ier )
C
C* Check to see if the header items needs byte-swapping.
C
IF ( iadir (2) .ne. 4 ) THEN
C
imbswp = 1
C
C* Swap bytes in AREA DIR except comment.
C
ier = MV_SWP4 ( 24, iadir ( 1 ), iadir ( 1 ) )
ier = MV_SWP4 ( 19, iadir ( 33 ), iadir ( 33 ) )
ier = MV_SWP4 ( 3, iadir ( 54 ), iadir ( 54 ) )
ier = MV_SWP4 ( 7, iadir ( 58 ), iadir ( 58 ) )
C
C* Swap bytes in NAV block except 1st word (nav label).
C
ier = MV_SWP4 ( 640-1, ianav ( 2 ) , ianav ( 2 ) )
C
ELSE
imbswp = 0
END IF
C
C* Determine calibration type Calibrations: 'RAW'
C* 'BRIT'
C* 'TEMP'
C
CALL ST_ITOC ( iadir (53), 1, cmcalb, ier )
C
C* Parse AREA data header.
C
imsorc = iadir ( 3 )
IF ( imsorc .eq. 7 ) then
imradf = 1
imtype = iadir ( 22 )
ELSE
imradf = 0
imtype = iadir ( 19 )
END IF
C
jyear = ( iadir ( 4 ) / 1000 ) + 1900
jday = MOD ( iadir ( 4 ), 1000 )
CALL TI_JTOI ( jyear, jday, idtarr, ier )
imdate = idtarr ( 1 ) * 10000 + idtarr ( 2 ) * 100 + idtarr ( 3 )
imtime = iadir ( 5 )
iullne = iadir ( 6 )
iulele = iadir ( 7 )
imnlin = iadir ( 9 )
imnpix = iadir ( 10 )
imdpth = iadir ( 11 )
rmyres = iadir ( 12 )
rmxres = iadir ( 13 )
imnchl = iadir ( 14 )
imprsz = iadir ( 15 )
imdcsz = iadir ( 49 )
imclsz = iadir ( 50 )
imlvsz = iadir ( 51 )
imvald = iadir ( 36 )
icaloff = iadir ( 63 )
if(icaloff.gt.0) CALL IM_CALIB(imgfil,icaloff,iret)
rmxysc = 1.0
C
C* Determine offset to start of data
C
IF ( iadir ( 34 ) .gt. 0 ) THEN
imdoff = iadir ( 34 )
ELSE
iret = -4
RETURN
END IF
imldat = imnlin * ( imnpix * imdpth * imnchl + imprsz )
C
C* Set image subset to full image for now.
C
imleft = 1
imtop = 1
imrght = imnpix
imbot = imnlin
C
C* Set navigation.
C
C* Standard latitude.
C
angdd = ianav ( 4 ) / 10000
angmm = ianav ( 4 ) / 100 - angdd * 100
angss = ianav ( 4 ) - angdd * 10000 - angmm * 100
stdlat = angdd + angmm / 60. + angss / 3600.
phi0 = stdlat
phi0r = phi0 * DTR
IF ( phi0r .lt. 0. ) sign = - 1.
C
C* Normal longitude. If west positive, make west negative.
C
angdd = ianav ( 6 ) / 10000
angmm = ianav ( 6 ) / 100 - angdd * 100
angss = ianav ( 6 ) - angdd * 10000 - angmm * 100
clon = angdd + angmm / 60. + angss / 3600.
IF ( ianav ( 10 ) .ge. 0 ) clon = - clon
C
C* Set pixel/grid dimension.
C
rgx = imnpix
rgy = imnlin
C
C* Location of pole point (rxp, ryp); (1,1) at lower-left corner.
C
rxp = float ( ianav ( 3 ) - iadir ( 7 ) ) / iadir ( 13 ) + 1.
ryp = rgy - float ( ianav ( 2 ) - iadir ( 6 ) ) / iadir ( 12 )
C
CALL ST_ITOC ( ianav, 1, navtyp, ier )
C
C* ******************************************
C* *** Satellite projection (MCIDAS GOES) ***
C* ******************************************
C
IF ( navtyp .eq. 'GOES' .or. navtyp .eq. 'GVAR' ) THEN
C
CALL GSATMG ( imgfil, iadir, ianav, imleft, imtop, imrght,
+ imbot, ier )
RETURN
C
C* ***************************
C* *** Polar Stereographic ***
C* ***************************
C
ELSE IF ( navtyp .eq. 'PS' ) THEN
C
C* Set pixel/grid spacing and earth radius.
C
dx = ianav ( 5 ) * iadir ( 13 )
re = ianav ( 8 )
if (re .le. 6200000.) re = RADIUS
C
C* Compute lat/lon of the lower-left corner.
C
dxp = 1. - rxp
dyp = 1. - ryp
alpha = 1. + SIN ( ABS ( phi0r ) )
rm = dx * SQRT ( dxp * dxp + dyp * dyp ) / alpha
c dlat1 = sign * ( HALFPI - 2. * ATAN ( rm / RADIUS ) ) * RTD
dlat1 = sign * ( HALFPI - 2. * ATAN ( rm / re ) ) * RTD
IF ( dyp .ne. 0. ) THEN
dyp = - dyp * sign
thta = ATAN2 ( dxp, dyp ) * RTD
dlon1 = clon + thta
CALL PRNLON ( 1, dlon1, ier )
ELSE
dlon1 = clon
END IF
C
C* Compute lat/lon of the upper-right corner.
C
dxp = rgx - rxp
dyp = rgy - ryp
rm = dx * SQRT ( dxp * dxp + dyp * dyp ) / alpha
c dlat2 = sign * ( HALFPI - 2. * ATAN ( rm / RADIUS ) ) * RTD
dlat2 = sign * ( HALFPI - 2. * ATAN ( rm / re ) ) * RTD
IF ( dyp .ne. 0. ) THEN
dyp = - dyp * sign
thta = ATAN2 ( dxp, dyp ) * RTD
dlon2 = clon + thta
CALL PRNLON ( 1, dlon2, iret )
ELSE
dlon2 = clon
END IF
C
C* Set map projection angles. Angle 2 is the central longitude.
C
IF ( stdlat .ge. 0. ) THEN
dangl1 = 90.
ELSE
dangl1 = - 90.
END IF
dangl2 = clon
dangl3 = 0.
proj = 'STR'
C
C* ****************
C* *** Mercator ***
C* ****************
C
ELSE IF ( navtyp .eq. 'MERC' ) THEN
C
C* Set pixel/grid spacing and earth radius and eccentricity.
C
dx = ianav ( 5 ) * iadir ( 13 )
re = ianav ( 7 )
if (re .le. 6200000.) re = RADIUS
ecc = ianav ( 8 ) / 1000000.
C
C* Compute lat/lon of the lower-left corner.
C
dxp = 1. - rxp
dyp = 1. - ryp
rm = dx * dyp
c rcos = RADIUS * COS ( phi0r )
rcos = re * COS ( phi0r )
arg = EXP ( rm / rcos )
dlat1 = ( 2. * ATAN ( arg ) - HALFPI ) * RTD
dlon1 = clon + ( dx * dxp / rcos ) * RTD
CALL PRNLON ( 1, dlon1, ier )
C
C* Compute lat/lon of the upper-right corner point.
C
dxp = rgx - rxp
dyp = rgy - ryp
rm = dx * dyp
arg = EXP ( rm / rcos )
dlat2 = ( 2. * ATAN ( arg ) - HALFPI ) * RTD
dlon2 = clon + ( dx * dxp / rcos ) * RTD
CALL PRNLON ( 1, dlon2, ier )
C
C* Set the map projection and angles.
C
dangl1 = 0.
dangl2 = clon
dangl3 = 0.
proj = 'MER'
C
C* *************************
C* *** Lambert Conformal ***
C* *************************
C
ELSE IF ( navtyp .eq. 'LAMB' ) THEN
C
C* Set pixel/grid spacing and earth radius and eccentricity.
C
dx = ianav ( 5 ) * iadir ( 13 )
re = ianav ( 8 )
if (re .le. 6200000.) re = RADIUS
C
C* Standard latitude #1
C
std1 = stdlat
C
C* Standard latitude #2
C
angdd = ianav ( 5 ) / 10000
angmm = ianav ( 5 ) / 100 - angdd * 100
angss = ianav ( 5 ) - angdd * 10000 - angmm * 100
std2 = angdd + angmm / 60. + angss / 3600.
C
C* Normal longitude. If west positive, make west negative.
C
angdd = ianav ( 7 ) / 10000
angmm = ianav ( 7 ) / 100 - angdd * 100
angss = ianav ( 7 ) - angdd * 10000 - angmm * 100
clon = angdd + angmm / 60. + angss / 3600.
IF ( ianav ( 10 ) .ge. 0 ) clon = - clon
C
C* Compute pixel/grid spacing and colatitudes.
C
dx = ianav ( 6 ) * iadir ( 13 )
psi1 = HALFPI - ABS ( std1 ) * DTR
psi2 = HALFPI - ABS ( std2 ) * DTR
C
C* Compute cone constant.
C
IF ( psi1 .eq. psi2 ) THEN
ccone = COS ( psi1 )
ELSE
tmp1 = ALOG ( SIN ( psi2 ) / SIN ( psi1 ) )
tmp2 = ALOG ( TAN ( psi2 / 2. ) / TAN ( psi1 / 2. ) )
ccone = tmp1 / tmp2
END IF
C
C* Compute lat/lon of the lower-left corner. Sign = 1/-1
C* denotes NH/SH.
C
dxp = 1. - rxp
dyp = 1. - ryp
rm = dx * SQRT ( dxp * dxp + dyp * dyp )
c tmp = ccone / ( RADIUS * SIN ( psi1 ) )
tmp = ccone / ( re * SIN ( psi1 ) )
arg = ( rm * tmp ) ** ( 1. / ccone ) * TAN ( psi1 / 2. )
dlat1 = sign * ( HALFPI - 2. * ATAN ( arg ) ) * RTD
C
IF ( dyp .ne. 0. ) THEN
dyp = - dyp
thta = ATAN2 ( dxp, dyp ) * RTD / ccone
dlon1 = clon + thta
CALL PRNLON ( 1, dlon1, ier )
ELSE
dlon1 = clon
END IF
C
C* Compute lat/lon of the upper-right corner.
C
dxp = rgx - rxp
dyp = rgy - ryp
rm = dx * SQRT ( dxp * dxp + dyp * dyp )
arg = ( rm * tmp ) ** ( 1. / ccone ) * TAN ( psi1 / 2. )
dlat2 = sign * ( HALFPI - 2. * ATAN ( arg ) ) * RTD
IF ( dyp .ne. 0. ) THEN
dyp = - dyp
thta = ATAN2 ( dxp, dyp ) * RTD / ccone
dlon2 = clon + thta
CALL PRNLON ( 1, dlon2, ier )
ELSE
dlon2 = clon
END IF
C
C* Northern or Southern Hemisphere projection
C
IF ( ( std1 + std2 ) .gt. 0. ) THEN
proj = 'LCC'
ELSE
proj = 'SCC'
END IF
dangl1 = std1
dangl2 = clon
dangl3 = std2
C
C* *************
C* *** Radar ***
C* *************
C
ELSE IF ( navtyp .eq. 'RADR' ) THEN
C
C* Get radar site info. Assume radar site is center of image.
C
rrow = ianav ( 2 )
rcol = ianav ( 3 )
C
C* Reference latitude.
C
dlat = stdlat
C
C* Reference longitude - convert to GEMPAK convention.
C
angdd = ianav ( 5 ) / 10000
angmm = ianav ( 5 ) / 100 - angdd * 100
angss = ianav ( 5 ) - angdd * 10000 - angmm * 100
dlon = angdd + angmm / 60. + angss / 3600.
dlon = - dlon
C
C* Pixel resolution, north rotation (not used).
C
pxresx = ianav ( 6 )
pxresy = pxresx
xrot = ianav ( 7 ) / 1000. * DTR
C
C* Calculate lat/lon pixel resolutions in radians
C
c rlatpx = ( RADIUS * DTR ) / pxresy
c rlonpx = ( RADIUS * DTR ) / pxresx
rlatpx = ( re * DTR ) / pxresy
rlonpx = ( re * DTR ) / pxresx
C
C* Determine lower-left lat/lon.
C
yline = imnlin + iullne - 1
xelem = iulele
C
dyline = rrow - yline
dxelem = rcol - xelem
dlat1 = dlat + dyline / rlatpx
dlon1 = dlon - dxelem / ( rlonpx * COS ( dlat1 * DTR ) )
C
C* Determine upper-right lat/lon coords.
C
yline = iullne
xelem = imnpix + iulele - 1
C
dyline = rrow - yline
dxelem = rcol - xelem
dlat2 = dlat + dyline / rlatpx
dlon2 = dlon - dxelem / ( rlonpx * COS ( dlat2 * DTR) )
C
C* Set the map projection
C
dangl1 = dlat
dangl2 = dlon
dangl3 = 0.
proj = 'STR'
C
C* *******************
C* *** Rectilinear ***
C* *******************
C
ELSE IF ( navtyp .eq. 'RECT' ) THEN
C
C* Row/column and lat/lon of reference point.
C
rrow = ianav ( 2 )
rcol = ianav ( 4 )
dlat = ianav ( 3 ) / 10000.
dlon = ianav ( 5 ) / 10000.
C
C* Determine longitude convention.
C
IF ( ianav ( 11 ) .ge. 0 ) sign = - 1.
dlon = sign * dlon
C
C* Lat/lon resolution (degrees/imageline).
C* Check for scaling factor. If it is not present use the
C* default scaling.
C
IF ( ianav ( 14 ) .eq. 0 ) THEN
reslat = ianav ( 6 ) / 10000.
ELSE
reslat = ianav ( 6 ) / ( 10. ** ianav (14) )
END IF
IF ( ianav ( 15 ) .eq. 0 ) THEN
reslon = ianav ( 7 ) / 10000.
ELSE
reslon = ianav ( 7 ) / ( 10. ** ianav (15) )
END IF
C
C* Determine upper-left lat/lon
C* (McIDAS image full coordinates 1,1).
C
uldlat = dlat + reslat * ( rrow - iullne )
uldlon = dlon + reslon * sign * ( rcol - iulele )
C
C* Lat/lon for lower-left corner.
C
dlat1 = uldlat - ( reslat * (imnlin * rmyres - 1))
dlon1 = uldlon
C
C* Lat/lon for upper-right corner.
C
dlat2 = uldlat
dlon2 = uldlon - sign * ( reslon * (imnpix * rmxres - 1) )
C
C* Set angle1 to the lon/lat aspect ratio.
C* Set angle2 to the central longitude.
C
dangl1 = reslon / reslat
dangl2 = uldlon -
+ sign * ( reslon * ( (imnpix * rmxres) / 2 - 1 ) )
dangl3 = 0.
proj = 'MCD'
C
C* Not valid
C
ELSE
iret = -5
RETURN
END IF
C
C* Set navigation blocks.
C
CALL GR_MNAV ( proj, imnpix, imnlin, dlat1, dlon1, dlat2,
+ dlon2, dangl1, dangl2, dangl3, .true.,
+ rnvblk, ier )
C
C* Set map projection.
C
CALL GSMPRJ ( proj, dangl1, dangl2, dangl3,
+ dlat1, dlon1, dlat2, dlon2, ier )
IF ( ier .ne. 0 ) iret = -5
C
RETURN
END
========================= imar2gm.f ====================
--
David Ovens e-mail: address@hidden
(206) 685-8108 plan: Real-time MM5 forecasting for Pacific Northwest
Research Meteorologist
Dept of Atmospheric Sciences, Box 351640
University of Washington
Seattle, WA 98195
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