hrap.c

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/*=========================================================================*/
/*                    FILE PATH/NAME:  STAGE3_SOURCE/hrap.c                */
/*                                                                         */
/*  FUNCTIONS CONTAINED IN THIS FILE:   HrapToLatLong                      */
/*                                      LatLongToHrap                      */
/*=========================================================================*/
 
#include "prototypes.h"
 
/***************************************************************************/
/* FILE PATH/NAME:  STAGE3_SOURCE/hrap.c                                   */
/*  FUNCTION NAME:   HrapToLatLong                                         */
/*       FUNCTION:   convert from HRAP coordinates to latitude-longitude   */
/****************************************************************************/
 
/*
Function type:
   HRAP structure
 
Called by function:
   (callback) locate
 
Functions called:
   none
 
Global variables:
   HrapToLatLong - function
   LatLongToHrap - function
 
Local variables:
   tlat - float; standard latitude in radians
   earthr - float; earth's radius (km)
   xmesh - float; mesh length at 60 deg North
   raddeg - float; conversion from radians to degrees
   stlon - float; standard longitude
   ll - HRAP structure; latitude/longitude */
 
/******************************************** BEGIN HrapToLatLong ***********/
 
struct HRAP HrapToLatLong(hrap)
   struct HRAP hrap;
{
   double x, y, rr, gi, ang;
   double tlat, earthr, xmesh, raddeg, stlon;
   struct HRAP  ll;
 
 earthr=6371.2;
 stlon=105.;
 raddeg=57.29577951;
 xmesh=4.7625;
 tlat=60./raddeg;
 
 x = (double)hrap.x - 401.;
 y = (double)hrap.y - 1601.;
 rr = x*x + y*y;
 gi = ((earthr * (1+sin(tlat)))/xmesh);
 gi=gi*gi;
 ll.y = asin((gi-rr)/(gi+rr))*raddeg;
 ang = atan2(y,x)*raddeg;
 if (ang < 0) ang=ang+360.;
 ll.x = 270+stlon-ang;
 if (ll.x < 0) ll.x=ll.x+360;
 if (ll.x > 360) ll.x=ll.x-360;
 return ll;
}
 
/********************************************* END HrapToLatLong ***********/
 
 
 
/***************************************************************************/
/* FILE PATH/NAME:  STAGE3_SOURCE/hrap.c                                   */
/*  FUNCTION NAME:   LatLongToHrap                                         */
/*       FUNCTION:   convert latitude-longitude coordinates to DV point    */
/*                    structure at appropriate screen position             */
/***************************************************************************
 
Function type:
   HRAP structure
 
Called by function:
 
Functions called:
   none
 
Global variables:
   HrapToLatLong - function
   LatLongToHrap - function
 
Local variables:
   lat - float; latitude
   lon - float; longitude
   degrad - float; conversion degrees to radians
   earthrad - float; radius of earth
   stdlat - float; standard latitude
   stdlon - float; standard longitude
   mesh_len - float; grid mesh length at standard latitude
   tlat - float; standard latitude in radians
   latrad - float; point latitude in radians
   lonrad - float; point longitude in radians
   hrap - HRAP structure; hrap coordinate
 
******************************************** BEGIN LatLongToHrap ***********/
 
struct HRAP LatLongToHrap(float lat, float lon)
   
{
   double  degrad = 0.017453293;
   double  earthrad = 6371.2;
   double  stdlat = 60.;
   double  stdlon = 105.;
   double  mesh_len = 4.7625;
   double  tlat, re, latrad, lonrad, r, x, y;
   struct HRAP   hrap;
 
 tlat = stdlat*degrad;
 re = (earthrad*(1. + sin(tlat)))/mesh_len;
 latrad = lat * degrad;
 lonrad = (lon + 180. - stdlon) * degrad;
 r = re * cos(latrad) / (1. + sin(latrad));
 x = r * sin(lonrad);
 y = r * cos(lonrad);
 hrap.x = x + 401;
 hrap.y = y + 1601;
 return hrap;
}
 
/********************************************* END LatLongToHrap ***********/
 
/********* BEGIN stageiii_structures.h ***************/
 
/*
#include <X11/Intrinsic.h>
 
typedef struct HRAP {
   float x,y;} HRAP;
 
typedef struct {
   int x,y;
   } point;
 
 
typedef struct {
    char id[4];
    float xlat;
    float xlong;
    int   on;
    HRAP  ctr;
    int   ngrd;
    } nex_struct;
 
 
typedef struct
    {
        short int    **data_array;
        int    maximum_columns, maximum_rows;
        int    num_levels;
        int    *levels;
        int    states_on;
        int    county_on;
        int    rivers_on;
         int    basins_on;
        int    rings_on;
        int    cities_on;
        int   ssnum;
        point  origin;
        GC     *gc;
        Pixmap pix;
        Pixmap pixbase;
        Widget w;
      } draw_struct; */
/**************** END stageiii_structures.h *****/