;
;==========================================================================
;
; FILE: mapearth.pro
;
; USAGE:  mapearth, roll, pitch, head, alt, azi, tau, sfc_rg, gs, alat, alon
;         ARGUMENTS:  roll    Aircraft roll
;                     pitch   Aircraft pitch
;                     head    Aircraft heading
;		      alt     Aircraft altitude (in km)
;                     azi     Azimuthal poistion of beam
;		      tau     Nominal incidence angle
;		      sfc_rg  First range gate that intersects surface
;		      gs      Gate spacing (in km)
;                     alat    Latitude of storm center closest to pass
;                     alon    Longitude of storm center closest to pass
;
;	  GIVES BACK:  ilat, ilon, ihgt.  Latitude, Longitude and Height (above surface) of pulse volume centers
;
; ABSTRACT: Compute radar pulse volume locations relative to Earth and 
;           centered on the storm.
;
; AUTHOR:  Steve Guimond
;          Postdoctoral Fellow (ORAU)
;	   NASA Goddard Space Flight Center
;          Code 613.1
;          Greenbelt, MD 20771
;          Email: stephen.guimond@nasa.gov
;
;==========================================================================

PRO mapearth, roll, pitch, head, alt, azi, tau, sfc_rg, gs, alat, alon

cosR = cos(roll*!dtor)
sinR = sin(roll*!dtor)
cosP = cos(pitch*!dtor)
sinP = sin(pitch*!dtor)
cosH = cos(head*!dtor)
sinH = sin(head*!dtor)
cosTheta = cos(azi*!dtor)
sinTheta = sin(azi*!dtor)
cosTau = cos(tau*!dtor)
sinTau = sin(tau*!dtor)

A = cosR*sinTheta*sinTau - sinR*cosTau
B = cosP*cosTheta + sinP*sinR*sinTheta
C = sinP*cosR*cosTau

FOR i=1,sfc_rg DO BEGIN
Xe(*,*,i) = (i*gs)*(cosH*A + sinH*sinTau*B + sinH*C)
Ye(*,*,i) = (i*gs)*(-sinH*A + cosH*sinTau*B + cosH*C)
Ze(*,*,i) = (i*gs)*(sinTau*(sinP*cosTheta - cosP*sinR*sinTheta) - cosP*cosR*cosTau)

;Lat/Lon/Height of HIWRAP measurements
ilat(*,*,i) = alat + Ye(*,*,i)/111					;degrees
ilon(*,*,i) = (alon+360) + Xe(*,*,i)/(111*cos(ilat(*,*,i)*!dtor))       ;degrees
ihgt(*,*,i) = alt/1000 + Ze(*,*,i)	                                ;km
ENDFOR

RETURN
END