/usr/share/doc/libplplot12/examples/c/x19c.c is in libplplot-dev 5.10.0+dfsg2-0.1ubuntu2.
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//
// Illustrates backdrop plotting of world, US maps.
// Contributed by Wesley Ebisuzaki.
//
#include "plcdemos.h"
void map_transform( PLFLT x, PLFLT y, PLFLT *xt, PLFLT *yt, PLPointer data );
void mapform19( PLINT n, PLFLT *x, PLFLT *y );
PLFLT normalize_longitude( PLFLT lon );
void geolocation_labeler( PLINT axis, PLFLT value, char *label, PLINT length, PLPointer data );
void
map_transform( PLFLT x, PLFLT y, PLFLT *xt, PLFLT *yt, PLPointer PL_UNUSED( data ) )
{
double radius;
radius = 90.0 - y;
*xt = radius * cos( x * M_PI / 180.0 );
*yt = radius * sin( x * M_PI / 180.0 );
}
//--------------------------------------------------------------------------
// mapform19
//
// Defines specific coordinate transformation for example 19.
// Not to be confused with mapform in src/plmap.c.
// x[], y[] are the coordinates to be plotted.
//--------------------------------------------------------------------------
void
mapform19( PLINT n, PLFLT *x, PLFLT *y )
{
int i;
double xp, yp;
for ( i = 0; i < n; i++ )
{
map_transform( x[i], y[i], &xp, &yp, NULL );
x[i] = xp;
y[i] = yp;
}
}
// "Normalize" longitude values so that they always fall between -180.0 and
// 180.0
PLFLT
normalize_longitude( PLFLT lon )
{
PLFLT times;
if ( lon >= -180.0 && lon <= 180.0 )
{
return ( lon );
}
else
{
times = floor( ( fabs( lon ) + 180.0 ) / 360.0 );
if ( lon < 0.0 )
{
return ( lon + 360.0 * times );
}
else
{
return ( lon - 360.0 * times );
}
}
}
// A custom axis labeling function for longitudes and latitudes.
void
geolocation_labeler( PLINT axis, PLFLT value, char *label, PLINT length, PLPointer PL_UNUSED( data ) )
{
const char *direction_label = NULL;
PLFLT label_val = 0.0;
if ( axis == PL_Y_AXIS )
{
label_val = value;
if ( label_val > 0.0 )
{
direction_label = " N";
}
else if ( label_val < 0.0 )
{
direction_label = " S";
}
else
{
direction_label = "Eq";
}
}
else if ( axis == PL_X_AXIS )
{
label_val = normalize_longitude( value );
if ( label_val > 0.0 )
{
direction_label = " E";
}
else if ( label_val < 0.0 )
{
direction_label = " W";
}
else
{
direction_label = "";
}
}
if ( axis == PL_Y_AXIS && value == 0.0 )
{
// A special case for the equator
snprintf( label, (size_t) length, "%s", direction_label );
}
else
{
snprintf( label, (size_t) length, "%.0f%s", fabs( label_val ), direction_label );
}
}
//--------------------------------------------------------------------------
// main
//
// Shows two views of the world map.
//--------------------------------------------------------------------------
int
main( int argc, const char **argv )
{
PLFLT minx, maxx, miny, maxy;
PLFLT x, y;
// Parse and process command line arguments
(void) plparseopts( &argc, argv, PL_PARSE_FULL );
// Longitude (x) and latitude (y)
miny = -70;
maxy = 80;
plinit();
// Cartesian plots
// Most of world
minx = -170;
maxx = minx + 360;
// Setup a custom latitude and longitude-based scaling function.
plslabelfunc( geolocation_labeler, NULL );
plcol0( 1 );
plenv( minx, maxx, miny, maxy, 1, 70 );
plmap( NULL, "usaglobe", minx, maxx, miny, maxy );
// The Americas
minx = 190;
maxx = 340;
plcol0( 1 );
plenv( minx, maxx, miny, maxy, 1, 70 );
plmap( NULL, "usaglobe", minx, maxx, miny, maxy );
// Clear the labeling function
plslabelfunc( NULL, NULL );
// Polar, Northern hemisphere
minx = 0;
maxx = 360;
plenv( -75., 75., -75., 75., 1, -1 );
plmap( mapform19, "globe", minx, maxx, miny, maxy );
pllsty( 2 );
plmeridians( mapform19, 10.0, 10.0, 0.0, 360.0, -10.0, 80.0 );
// Polar, Northern hemisphere, this time with a PLplot-wide transform
minx = 0;
maxx = 360;
plstransform( map_transform, NULL );
pllsty( 1 );
plenv( -75., 75., -75., 75., 1, -1 );
// No need to set the map transform here as the global transform will be
// used.
plmap( NULL, "globe", minx, maxx, miny, maxy );
pllsty( 2 );
plmeridians( NULL, 10.0, 10.0, 0.0, 360.0, -10.0, 80.0 );
// Show Baltimore, MD on the map
plcol0( 2 );
plssym( 0.0, 2.0 );
x = -76.6125;
y = 39.2902778;
plpoin( 1, &x, &y, 18 );
plssym( 0.0, 1.0 );
plptex( -76.6125, 43.0, 0.0, 0.0, 0.0, "Baltimore, MD" );
// For C, this is how the global transform is cleared
plstransform( NULL, NULL );
plend();
exit( 0 );
}
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