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/* topo.c */
/*
* Earth topography
*/
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "binio.h"
static float Topo_westlon, Topo_eastlon, Topo_northlat, Topo_southlat;
static int Topo_rows, Topo_cols;
static short *TopoData;
/*** load_topo ********************************************************
Read a topography file and initialize Topo and TopoData.
Input: filename - name of topo file.
Return: 0 if error, otherwise non-zero for success.
**********************************************************************/
int load_topo( char filename[] )
{
static int already_loaded = 0;
int f;
char id[40];
if (!already_loaded) {
f = open( filename, O_RDONLY );
if (f<0) {
/* printf("Topo file %s not found\n", filename );*/
return 0;
}
/* Read file header */
read_bytes( f, id, 40 );
if (strcmp(id,"TOPO")==0) {
/* OLD STYLE: bounds given as ints */
int k;
read_int4( f, &k ); Topo_westlon = k / 100.0;
read_int4( f, &k ); Topo_eastlon = k / 100.0;
read_int4( f, &k ); Topo_northlat = k / 100.0;
read_int4( f, &k ); Topo_southlat = k / 100.0;
}
else if (strcmp(id,"TOPO2")==0) {
/* NEW STYLE: bounds given as floats */
read_float4( f, &Topo_westlon );
read_float4( f, &Topo_eastlon );
read_float4( f, &Topo_northlat );
read_float4( f, &Topo_southlat );
}
else {
printf("%s is not a TOPO file\n", filename);
close(f);
return 0;
}
read_int4( f, &Topo_rows );
read_int4( f, &Topo_cols );
/* allocate storage for the topo values */
TopoData = (short *) malloc( Topo_rows*Topo_cols*sizeof(short) );
if (!TopoData) {
close(f);
return 0;
}
/* read the topo values */
read_int2_array( f, TopoData, Topo_rows*Topo_cols );
/* all done */
close(f);
already_loaded = 1;
}
return 1;
}
static int LatSamples = 1;
static int LonSamples = 1;
/*
* Before calling the elevation function below, one should first call
* this function to indicate approximately how many degrees of latitude
* and longitude are between adjacent samplings (i.e. calls to elevation()).
* With this hint we can determine how many samples of the topography to
* take then average together in the elevation() function.
* Input: latres - latitude resolution
* lonres - longitude resolution
*/
void set_topo_sampling( float latres, float lonres )
{
LatSamples = (int) (latres / ((Topo_northlat-Topo_southlat) / (Topo_rows-1)));
LonSamples = (int) (lonres / ((Topo_westlon-Topo_eastlon) / (Topo_cols-1)));
if (LatSamples<=0) LatSamples = 1;
if (LonSamples<=0) LonSamples = 1;
}
/* TODO: sampling */
/*** elevation ********************************************************
Return the elevation of the topography at location (lat,lon) and a
flag indicating water or land.
Input: lat, lon - location in degrees
water - pointer to integer
Output: water - set to 1 if water, 0 if land.
Returned: elevation in meters at (lat,lon) or 0 if error.
**********************************************************************/
float elevation( float lat, float lon, int *water )
{
float fr, fc;
int rowa, cola, rowb, colb;
float hgt;
int count, r, c;
int val, watcount;
if (!TopoData || lon<Topo_eastlon || lon>Topo_westlon
|| lat<Topo_southlat || lat>Topo_northlat) {
if (water)
*water = 0;
return 0.0;
}
/* Return elevation at (lat,lon) by sampling LatSamples x LonSamples */
/* values centered at that location. */
/* calculate range of rows */
fr = Topo_rows * (lat - Topo_northlat) / (Topo_southlat - Topo_northlat);
rowa = (int) fr - LatSamples/2;
rowb = rowa+LatSamples;
if (rowa<0)
rowa = 0;
if (rowb>=Topo_rows)
rowb = Topo_rows-1;
/* calculate range of columns */
fc = Topo_cols * (lon-Topo_westlon) / (Topo_eastlon - Topo_westlon);
cola = (int) fc - LonSamples/2;
colb = cola+LonSamples;
if (cola<0)
cola = 0;
if (colb>=Topo_cols)
colb = Topo_cols-1;
/* find average height in sample area */
hgt = 0.0;
count = watcount = 0;
for (r=rowa;r<=rowb;r++) {
for (c=cola;c<=colb;c++) {
val = TopoData[r*Topo_cols+c];
if (val&1)
watcount++;
hgt += (float) (val / 2);
count++;
}
}
hgt = hgt / (float) count;
/* calculate water flag */
if (water) {
if (watcount>count/2)
*water = 1;
else
*water = 0;
}
return hgt;
}
/*
* Deallocate memory used for storing topography.
*/
void free_topo( void )
{
if (TopoData) {
free( TopoData );
TopoData = NULL;
}
}
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