[andy/viking.git] / src / dem.c

/*
 * viking -- GPS Data and Topo Analyzer, Explorer, and Manager
 *
 * Copyright (C) 2003-2008, Evan Battaglia <gtoevan@gmx.net>
 * Copyright (C) 2007, Quy Tonthat <qtonthat@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <stdio.h>
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#include <glib.h>
#ifdef HAVE_MATH_H
#include <math.h>
#endif
#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#include <zlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

#include <glib/gstdio.h>
#include <glib/gi18n.h>

#include "dem.h"
#include "file.h"

#define DEM_BLOCK_SIZE 1024
#define GET_COLUMN(dem,n) ((VikDEMColumn *)g_ptr_array_index( (dem)->columns, (n) ))

static gboolean get_double_and_continue ( gchar **buffer, gdouble *tmp, gboolean warn )
{
  gchar *endptr;
  *tmp = g_strtod(*buffer, &endptr);
  if ( endptr == NULL|| endptr == *buffer ) {
    if ( warn )
      g_warning(_("Invalid DEM"));
    return FALSE;
  }
  *buffer=endptr;
  return TRUE;
}


static gboolean get_int_and_continue ( gchar **buffer, gint *tmp, gboolean warn )
{
  gchar *endptr;
  *tmp = strtol(*buffer, &endptr, 10);
  if ( endptr == NULL|| endptr == *buffer ) {
    if ( warn )
      g_warning(_("Invalid DEM"));
    return FALSE;
  }
  *buffer=endptr;
  return TRUE;
}

static gboolean dem_parse_header ( gchar *buffer, VikDEM *dem )
{
  gdouble val;
  gint int_val;
  guint i;
  gchar *tmp = buffer;

  /* incomplete header */
  if ( strlen(buffer) != 1024 )
    return FALSE;

  /* fix Fortran-style exponentiation 1.0D5 -> 1.0E5 */
  while (*tmp) {
    if ( *tmp=='D')
      *tmp='E';
    tmp++;
  }

  /* skip name */
  buffer += 149;

  /* "DEM level code, pattern code, palaimetric reference system code" -- skip */
  get_int_and_continue(&buffer, &int_val, TRUE);
  get_int_and_continue(&buffer, &int_val, TRUE);
  get_int_and_continue(&buffer, &int_val, TRUE);

  /* zone */
  get_int_and_continue(&buffer, &int_val, TRUE);
  dem->utm_zone = int_val;
  /* TODO -- southern or northern hemisphere?! */
  dem->utm_letter = 'N';

  /* skip numbers 5-19  */
  for ( i = 0; i < 15; i++ ) {
    if ( ! get_double_and_continue(&buffer, &val, FALSE) ) {
      g_warning (_("Invalid DEM header"));
      return FALSE;
    }
  }

  /* number 20 -- horizontal unit code (utm/ll) */
  get_double_and_continue(&buffer, &val, TRUE);
  dem->horiz_units = val;
  get_double_and_continue(&buffer, &val, TRUE);
  /* dem->orig_vert_units = val; now done below */

  /* TODO: do this for real. these are only for 1:24k and 1:250k USGS */
  if ( dem->horiz_units == VIK_DEM_HORIZ_UTM_METERS ) {
    dem->east_scale = 10.0; /* meters */
    dem->north_scale = 10.0;
    dem->orig_vert_units = VIK_DEM_VERT_DECIMETERS;
  } else {
    dem->east_scale = 3.0; /* arcseconds */
    dem->north_scale = 3.0;
    dem->orig_vert_units = VIK_DEM_VERT_METERS;
  }

  /* skip next */
  get_double_and_continue(&buffer, &val, TRUE);

  /* now we get the four corner points. record the min and max. */
  get_double_and_continue(&buffer, &val, TRUE);
  dem->min_east = dem->max_east = val;
  get_double_and_continue(&buffer, &val, TRUE);
  dem->min_north = dem->max_north = val;

  for ( i = 0; i < 3; i++ ) {
    get_double_and_continue(&buffer, &val, TRUE);
    if ( val < dem->min_east ) dem->min_east = val;
    if ( val > dem->max_east ) dem->max_east = val;
    get_double_and_continue(&buffer, &val, TRUE);
    if ( val < dem->min_north ) dem->min_north = val;
    if ( val > dem->max_north ) dem->max_north = val;
  }

  return TRUE;
}

static void dem_parse_block_as_cont ( gchar *buffer, VikDEM *dem, gint *cur_column, gint *cur_row )
{
  gint tmp;
  while ( *cur_row < GET_COLUMN(dem, *cur_column)->n_points ) {
    if ( get_int_and_continue(&buffer, &tmp,FALSE) ) {
      if ( dem->orig_vert_units == VIK_DEM_VERT_DECIMETERS )
        GET_COLUMN(dem, *cur_column)->points[*cur_row] = (gint16) (tmp / 10);
      else
        GET_COLUMN(dem, *cur_column)->points[*cur_row] = (gint16) tmp;
    } else
      return;
    (*cur_row)++;
  }
  *cur_row = -1; /* expecting new column */
}

static void dem_parse_block_as_header ( gchar *buffer, VikDEM *dem, gint *cur_column, gint *cur_row )
{
  guint n_rows;
  gint i;
  gdouble east_west, south;
  gdouble tmp;

  /* 1 x n_rows 1 east_west south x x x DATA */

  if ( (!get_double_and_continue(&buffer, &tmp, TRUE)) || tmp != 1 ) {
    g_warning(_("Incorrect DEM Class B record: expected 1"));
    return;
  }

  /* don't need this */
  if ( !get_double_and_continue(&buffer, &tmp, TRUE ) ) return;

  /* n_rows */
  if ( !get_double_and_continue(&buffer, &tmp, TRUE ) )
    return;
  n_rows = (guint) tmp;

  if ( (!get_double_and_continue(&buffer, &tmp, TRUE)) || tmp != 1 ) {
    g_warning(_("Incorrect DEM Class B record: expected 1"));
    return;
  }
  
  if ( !get_double_and_continue(&buffer, &east_west, TRUE) )
    return;
  if ( !get_double_and_continue(&buffer, &south, TRUE) )
    return;

  /* next three things we don't need */
  if ( !get_double_and_continue(&buffer, &tmp, TRUE)) return;
  if ( !get_double_and_continue(&buffer, &tmp, TRUE)) return;
  if ( !get_double_and_continue(&buffer, &tmp, TRUE)) return;


  dem->n_columns ++;
  (*cur_column) ++;

  /* empty spaces for things before that were skipped */
  (*cur_row) = (south - dem->min_north) / dem->north_scale;
  if ( south > dem->max_north || (*cur_row) < 0 )
    (*cur_row) = 0;

  n_rows += *cur_row;

  g_ptr_array_add ( dem->columns, g_malloc(sizeof(VikDEMColumn)) );
  GET_COLUMN(dem,*cur_column)->east_west = east_west;
  GET_COLUMN(dem,*cur_column)->south = south;
  GET_COLUMN(dem,*cur_column)->n_points = n_rows;
  GET_COLUMN(dem,*cur_column)->points = g_malloc(sizeof(gint16)*n_rows);

  /* no information for things before that */
  for ( i = 0; i < (*cur_row); i++ )
    GET_COLUMN(dem,*cur_column)->points[i] = VIK_DEM_INVALID_ELEVATION;

  /* now just continue */
  dem_parse_block_as_cont ( buffer, dem, cur_column, cur_row );


}

static void dem_parse_block ( gchar *buffer, VikDEM *dem, gint *cur_column, gint *cur_row )
{
  /* if haven't read anything or have read all items in a columns and are expecting a new column */
  if ( *cur_column == -1 || *cur_row == -1 ) {
    dem_parse_block_as_header(buffer, dem, cur_column, cur_row);
  } else {
    dem_parse_block_as_cont(buffer, dem, cur_column, cur_row);
  }
}

/* return size of unzip data or 0 if failed */
/* can be made generic to uncompress zip, gzip, bzip2 data */
static guint uncompress_data(void *uncompressed_buffer, guint uncompressed_size, void *compressed_data, guint compressed_size)
{
	z_stream stream;
	int err;

	stream.next_in = compressed_data;
	stream.avail_in = compressed_size;
	stream.next_out = uncompressed_buffer;
	stream.avail_out = uncompressed_size;
	stream.zalloc = (alloc_func)0;
	stream.zfree = (free_func)0;
	stream.opaque = (voidpf)0;

	/* negative windowBits to inflateInit2 means "no header" */
	if ((err = inflateInit2(&stream, -MAX_WBITS)) != Z_OK) {
		g_warning("%s(): inflateInit2 failed", __PRETTY_FUNCTION__);
		return 0;
	}

	err = inflate(&stream, Z_FINISH);
	if ((err != Z_OK) && (err != Z_STREAM_END) && stream.msg) {
		g_warning("%s() inflate failed err=%d \"%s\"", __PRETTY_FUNCTION__, err, stream.msg == NULL ? "unknown" : stream.msg);
		inflateEnd(&stream);
		return 0;
	}

	inflateEnd(&stream);
	return(stream.total_out);
}

static void *unzip_hgt_file(gchar *zip_file, gulong *unzip_size)
{
	void *unzip_data = NULL;
	gchar *zip_data;
	struct _lfh {
		guint32 sig;
		guint16 extract_version;
		guint16 flags;
		guint16 comp_method;
		guint16 time;
		guint16 date;
		guint32 crc_32;
		guint32 compressed_size;
		guint32 uncompressed_size;
		guint16 filename_len;
		guint16 extra_field_len;
	}  __attribute__ ((__packed__)) *local_file_header = NULL;


	local_file_header = (struct _lfh *) zip_file;
	if (local_file_header->sig != 0x04034b50) {
		g_warning("%s(): wrong format", __PRETTY_FUNCTION__);
		g_free(unzip_data);
		goto end;
	}

	zip_data = zip_file + sizeof(struct _lfh) + local_file_header->filename_len + local_file_header->extra_field_len;
	unzip_data = g_malloc(local_file_header->uncompressed_size);
	gulong uncompressed_size = local_file_header->uncompressed_size;

	if (!(*unzip_size = uncompress_data(unzip_data, uncompressed_size, zip_data, local_file_header->compressed_size))) {
		g_free(unzip_data);
		unzip_data = NULL;
		goto end;
	}

end:
	return(unzip_data);
}

static VikDEM *vik_dem_read_srtm_hgt(const gchar *file_name, const gchar *basename, gboolean zip)
{
  gint i, j;
  VikDEM *dem;
  off_t file_size;
  gint16 *dem_mem = NULL;
  gchar *dem_file = NULL;
  const gint num_rows_3sec = 1201;
  const gint num_rows_1sec = 3601;
  gint num_rows;
  GMappedFile *mf;
  gint arcsec;
  GError *error = NULL;

  dem = g_malloc(sizeof(VikDEM));

  dem->horiz_units = VIK_DEM_HORIZ_LL_ARCSECONDS;
  dem->orig_vert_units = VIK_DEM_VERT_DECIMETERS;

  /* TODO */
  dem->min_north = atoi(basename+1) * 3600;
  dem->min_east = atoi(basename+4) * 3600;
  if ( basename[0] == 'S' )
    dem->min_north = - dem->min_north;
  if ( basename[3] == 'W' )
    dem->min_east = - dem->min_east;

  dem->max_north = 3600 + dem->min_north;
  dem->max_east = 3600 + dem->min_east;

  dem->columns = g_ptr_array_new();
  dem->n_columns = 0;

  if ((mf = g_mapped_file_new(file_name, FALSE, &error)) == NULL) {
    g_error(_("Couldn't map file %s: %s"), file_name, error->message);
    g_error_free(error);
    g_free(dem);
    return NULL;
  }
  file_size = g_mapped_file_get_length(mf);
  dem_file = g_mapped_file_get_contents(mf);
  
  if (zip) {
    void *unzip_mem = NULL;
    gulong ucsize;

    if ((unzip_mem = unzip_hgt_file(dem_file, &ucsize)) == NULL) {
      g_mapped_file_free(mf);
      g_ptr_array_free(dem->columns, TRUE);
      g_free(dem);
      return NULL;
    }

    dem_mem = unzip_mem;
    file_size = ucsize;
  }

  if (file_size == (num_rows_3sec * num_rows_3sec * sizeof(gint16)))
    arcsec = 3;
  else if (file_size == (num_rows_1sec * num_rows_1sec * sizeof(gint16)))
    arcsec = 1;
  else {
    g_warning("%s(): file %s does not have right size", __PRETTY_FUNCTION__, basename);
    g_mapped_file_free(mf);
    g_free(dem);
    return NULL;
  }

  num_rows = (arcsec == 3) ? num_rows_3sec : num_rows_1sec;
  dem->east_scale = dem->north_scale = arcsec;

  for ( i = 0; i < num_rows; i++ ) {
    dem->n_columns++;
    g_ptr_array_add ( dem->columns, g_malloc(sizeof(VikDEMColumn)) );
    GET_COLUMN(dem,i)->east_west = dem->min_east + arcsec*i;
    GET_COLUMN(dem,i)->south = dem->min_north;
    GET_COLUMN(dem,i)->n_points = num_rows;
    GET_COLUMN(dem,i)->points = g_malloc(sizeof(gint16)*num_rows);
  }

  int ent = 0;
  for ( i = (num_rows - 1); i >= 0; i-- ) {
    for ( j = 0; j < num_rows; j++ ) {
      GET_COLUMN(dem,j)->points[i] = GINT16_FROM_BE(dem_mem[ent]);
      ent++;
    }

  }

  if (zip)
    g_free(dem_mem);
  g_mapped_file_free(mf);
  return dem;
}

#define IS_SRTM_HGT(fn) (strlen((fn))==11 && (fn)[7]=='.' && (fn)[8]=='h' && (fn)[9]=='g' && (fn)[10]=='t' && ((fn)[0]=='N' || (fn)[0]=='S') && ((fn)[3]=='E' || (fn)[3]=='W'))

VikDEM *vik_dem_new_from_file(const gchar *file)
{
  FILE *f=NULL;
  VikDEM *rv;
  gchar buffer[DEM_BLOCK_SIZE+1];

  /* use to record state for dem_parse_block */
  gint cur_column = -1;
  gint cur_row = -1;
  const gchar *basename = a_file_basename(file);

  if ( g_access ( file, R_OK ) != 0 )
    return NULL;

  if ( (strlen(basename)==11 || ((strlen(basename) == 15) && (basename[11] == '.' && basename[12] == 'z' && basename[13] == 'i' && basename[14] == 'p'))) &&
       basename[7]=='.' && basename[8]=='h' && basename[9]=='g' && basename[10]=='t' &&
       (basename[0] == 'N' || basename[0] == 'S') && (basename[3] == 'E' || basename[3] =='W')) {
    gboolean is_zip_file = (strlen(basename) == 15);
    rv = vik_dem_read_srtm_hgt(file, basename, is_zip_file);
    return(rv);
  }

      /* Create Structure */
  rv = g_malloc(sizeof(VikDEM));

      /* Header */
  f = g_fopen(file, "r");
  if ( !f ) {
    g_free ( rv );
    return NULL;
  }
  buffer[fread(buffer, 1, DEM_BLOCK_SIZE, f)] = '\0';
  if ( ! dem_parse_header ( buffer, rv ) ) {
    g_free ( rv );
    return NULL;
  }
  /* TODO: actually use header -- i.e. GET # OF COLUMNS EXPECTED */

  rv->columns = g_ptr_array_new();
  rv->n_columns = 0;

      /* Column -- Data */
  while (! feof(f) ) {
     gchar *tmp;

     /* read block */
     buffer[fread(buffer, 1, DEM_BLOCK_SIZE, f)] = '\0';

     /* Fix Fortran-style exponentiation */
     tmp = buffer;
     while (*tmp) {
       if ( *tmp=='D')
         *tmp='E';
       tmp++;
     }

     dem_parse_block(buffer, rv, &cur_column, &cur_row);
  }

     /* TODO - class C records (right now says 'Invalid' and dies) */

  fclose(f);
  f = NULL;

  /* 24k scale */
  if ( rv->horiz_units == VIK_DEM_HORIZ_UTM_METERS && rv->n_columns >= 2 )
    rv->north_scale = rv->east_scale = GET_COLUMN(rv, 1)->east_west - GET_COLUMN(rv,0)->east_west;

  /* FIXME bug in 10m DEM's */
  if ( rv->horiz_units == VIK_DEM_HORIZ_UTM_METERS && rv->north_scale == 10 ) {
    rv->min_east -= 100;
    rv->min_north += 200;
  }


  return rv;
}

void vik_dem_free ( VikDEM *dem )
{
  guint i;
  for ( i = 0; i < dem->n_columns; i++)
    g_free ( GET_COLUMN(dem, i)->points );
  g_ptr_array_free ( dem->columns, TRUE );
  g_free ( dem );
}

gint16 vik_dem_get_xy ( VikDEM *dem, guint col, guint row )
{
  if ( col < dem->n_columns )
    if ( row < GET_COLUMN(dem, col)->n_points )
      return GET_COLUMN(dem, col)->points[row];
  return VIK_DEM_INVALID_ELEVATION;
}

gint16 vik_dem_get_east_north ( VikDEM *dem, gdouble east, gdouble north )
{
  gint col, row;

  if ( east > dem->max_east || east < dem->min_east ||
      north > dem->max_north || north < dem->min_north )
    return VIK_DEM_INVALID_ELEVATION;

  col = (gint) floor((east - dem->min_east) / dem->east_scale);
  row = (gint) floor((north - dem->min_north) / dem->north_scale);

  return vik_dem_get_xy ( dem, col, row );
}

static gboolean dem_get_ref_points_elev_dist(VikDEM *dem,
    gdouble east, gdouble north, /* in seconds */
    gint16 *elevs, gint16 *dists)
{
  int i;
  int cols[4], rows[4];
  struct LatLon ll[4];
  struct LatLon pos;

  if ( east > dem->max_east || east < dem->min_east ||
      north > dem->max_north || north < dem->min_north )
    return FALSE;  /* got nothing */

  pos.lon = east/3600;
  pos.lat = north/3600;

  /* order of the data: sw, nw, ne, se */
  /* sw */
  cols[0] = (gint) floor((east - dem->min_east) / dem->east_scale);
  rows[0] = (gint) floor((north - dem->min_north) / dem->north_scale);
  ll[0].lon = (dem->min_east + dem->east_scale*cols[0])/3600;
  ll[0].lat = (dem->min_north + dem->north_scale*rows[0])/3600;
  /* nw */
  cols[1] = cols[0];
  rows[1] = rows[0] + 1;
  ll[1].lon = ll[0].lon;
  ll[1].lat = ll[0].lat + (gdouble)dem->north_scale/3600;
  /* ne */
  cols[2] = cols[0] + 1;
  rows[2] = rows[0] + 1;
  ll[2].lon = ll[0].lon + (gdouble)dem->east_scale/3600;
  ll[2].lat = ll[0].lat + (gdouble)dem->north_scale/3600;
  /* se */
  cols[3] = cols[0] + 1;
  rows[3] = rows[0];
  ll[3].lon = ll[0].lon + (gdouble)dem->east_scale/3600;
  ll[3].lat = ll[0].lat;

  for (i = 0; i < 4; i++) {
    if ((elevs[i] = vik_dem_get_xy(dem, cols[i], rows[i])) == VIK_DEM_INVALID_ELEVATION)
      return FALSE;
    dists[i] = a_coords_latlon_diff(&pos, &ll[i]);
  }

#if 0  /* debug */
  for (i = 0; i < 4; i++)
    fprintf(stderr, "%f:%f:%d:%d  ", ll[i].lat, ll[i].lon, dists[i], elevs[i]);
  fprintf(stderr, "   north_scale=%f\n", dem->north_scale);
#endif

  return TRUE;  /* all OK */
}

gint16 vik_dem_get_simple_interpol ( VikDEM *dem, gdouble east, gdouble north )
{
  int i;
  gint16 elevs[4], dists[4];

  if (!dem_get_ref_points_elev_dist(dem, east, north, elevs, dists))
    return VIK_DEM_INVALID_ELEVATION;

  for (i = 0; i < 4; i++) {
    if (dists[i] < 1) {
      return(elevs[i]);
    }
  }

  gdouble t = (gdouble)elevs[0]/dists[0] + (gdouble)elevs[1]/dists[1] + (gdouble)elevs[2]/dists[2] + (gdouble)elevs[3]/dists[3];
  gdouble b = 1.0/dists[0] + 1.0/dists[1] + 1.0/dists[2] + 1.0/dists[3];

  return(t/b);
}

gint16 vik_dem_get_shepard_interpol ( VikDEM *dem, gdouble east, gdouble north )
{
  int i;
  gint16 elevs[4], dists[4];
  gint16 max_dist;
  gdouble t = 0.0;
  gdouble b = 0.0;

  if (!dem_get_ref_points_elev_dist(dem, east, north, elevs, dists))
    return VIK_DEM_INVALID_ELEVATION;

  max_dist = 0;
  for (i = 0; i < 4; i++) {
    if (dists[i] < 1) {
      return(elevs[i]);
    }
    if (dists[i] > max_dist)
      max_dist = dists[i];
  }

  gdouble tmp;
#if 0 /* derived method by Franke & Nielson. Does not seem to work too well here */
  for (i = 0; i < 4; i++) {
    tmp = pow((1.0*(max_dist - dists[i])/max_dist*dists[i]), 2);
    t += tmp*elevs[i];
    b += tmp;
  }
#endif

  for (i = 0; i < 4; i++) {
    tmp = pow((1.0/dists[i]), 2);
    t += tmp*elevs[i];
    b += tmp;
  }

  // fprintf(stderr, "DEBUG: tmp=%f t=%f b=%f %f\n", tmp, t, b, t/b);

  return(t/b);

}

void vik_dem_east_north_to_xy ( VikDEM *dem, gdouble east, gdouble north, guint *col, guint *row )
{
  *col = (gint) floor((east - dem->min_east) / dem->east_scale);
  *row = (gint) floor((north - dem->min_north) / dem->north_scale);
  if ( *col < 0 ) *col = 0;
  if ( *row < 0 ) *row = 0;
}
Commit	Line	Data
f6171fe3 EB	1	/*
	2	* viking -- GPS Data and Topo Analyzer, Explorer, and Manager
	3	*
	4	* Copyright (C) 2003-2008, Evan Battaglia <gtoevan@gmx.net>
a482007a	5	* Copyright (C) 2007, Quy Tonthat <qtonthat@gmail.com>
f6171fe3 EB	6	*
	7	* This program is free software; you can redistribute it and/or modify
	8	* it under the terms of the GNU General Public License as published by
	9	* the Free Software Foundation; either version 2 of the License, or
	10	* (at your option) any later version.
	11	*
	12	* This program is distributed in the hope that it will be useful,
	13	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	14	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	15	* GNU General Public License for more details.
	16	*
	17	* You should have received a copy of the GNU General Public License
	18	* along with this program; if not, write to the Free Software
	19	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	20	*
	21	*/
	22
72b6a3ed JB	23	#ifdef HAVE_CONFIG_H
	24	#include "config.h"
	25	#endif
	26
ad0a8c2d	27	#include <stdio.h>
8c00358d	28	#ifdef HAVE_STRING_H
ad0a8c2d	29	#include <string.h>
8c00358d	30	#endif
ad0a8c2d	31	#include <glib.h>
8c00358d	32	#ifdef HAVE_MATH_H
ad0a8c2d	33	#include <math.h>
8c00358d GB	34	#endif
8c00358d GB	35	#ifdef HAVE_STDLIB_H
ad0a8c2d	36	#include <stdlib.h>
8c00358d	37	#endif
46e4fa54 QT	38	#include <zlib.h>
	39	#include <sys/types.h>
	40	#include <sys/stat.h>
31766324 MA	41	#ifdef HAVE_UNISTD_H
	42	#include <unistd.h>
	43	#endif
46e4fa54	44
6af463da	45	#include <glib/gstdio.h>
4c77d5e0 GB	46	#include <glib/gi18n.h>
4c77d5e0 GB	47
ad0a8c2d EB	48	#include "dem.h"
	49	#include "file.h"
	50
	51	#define DEM_BLOCK_SIZE 1024
	52	#define GET_COLUMN(dem,n) ((VikDEMColumn *)g_ptr_array_index( (dem)->columns, (n) ))
	53
	54	static gboolean get_double_and_continue ( gchar *buffer, gdouble tmp, gboolean warn )
	55	{
	56	gchar *endptr;
	57	tmp = g_strtod(buffer, &endptr);
	58	if ( endptr == NULL\|\| endptr == *buffer ) {
	59	if ( warn )
4c77d5e0	60	g_warning(_("Invalid DEM"));
ad0a8c2d EB	61	return FALSE;
	62	}
	63	*buffer=endptr;
	64	return TRUE;
	65	}
	66
	67
	68	static gboolean get_int_and_continue ( gchar *buffer, gint tmp, gboolean warn )
	69	{
	70	gchar *endptr;
	71	tmp = strtol(buffer, &endptr, 10);
	72	if ( endptr == NULL\|\| endptr == *buffer ) {
	73	if ( warn )
4c77d5e0	74	g_warning(_("Invalid DEM"));
ad0a8c2d EB	75	return FALSE;
	76	}
	77	*buffer=endptr;
	78	return TRUE;
	79	}
	80
	81	static gboolean dem_parse_header ( gchar buffer, VikDEM dem )
	82	{
	83	gdouble val;
	84	gint int_val;
	85	guint i;
	86	gchar *tmp = buffer;
	87
	88	/* incomplete header */
	89	if ( strlen(buffer) != 1024 )
	90	return FALSE;
	91
	92	/* fix Fortran-style exponentiation 1.0D5 -> 1.0E5 */
	93	while (*tmp) {
	94	if ( *tmp=='D')
	95	*tmp='E';
	96	tmp++;
	97	}
	98
	99	/* skip name */
	100	buffer += 149;
	101
	102	/* "DEM level code, pattern code, palaimetric reference system code" -- skip */
	103	get_int_and_continue(&buffer, &int_val, TRUE);
	104	get_int_and_continue(&buffer, &int_val, TRUE);
	105	get_int_and_continue(&buffer, &int_val, TRUE);
	106
	107	/* zone */
	108	get_int_and_continue(&buffer, &int_val, TRUE);
	109	dem->utm_zone = int_val;
	110	/* TODO -- southern or northern hemisphere?! */
	111	dem->utm_letter = 'N';
	112
	113	/* skip numbers 5-19 */
	114	for ( i = 0; i < 15; i++ ) {
	115	if ( ! get_double_and_continue(&buffer, &val, FALSE) ) {
4c77d5e0	116	g_warning (_("Invalid DEM header"));
ad0a8c2d EB	117	return FALSE;
	118	}
	119	}
	120
	121	/* number 20 -- horizontal unit code (utm/ll) */
	122	get_double_and_continue(&buffer, &val, TRUE);
	123	dem->horiz_units = val;
	124	get_double_and_continue(&buffer, &val, TRUE);
70147e60	125	/* dem->orig_vert_units = val; now done below */
ad0a8c2d EB	126
	127	/* TODO: do this for real. these are only for 1:24k and 1:250k USGS */
	128	if ( dem->horiz_units == VIK_DEM_HORIZ_UTM_METERS ) {
	129	dem->east_scale = 10.0; /* meters */
	130	dem->north_scale = 10.0;
70147e60	131	dem->orig_vert_units = VIK_DEM_VERT_DECIMETERS;
ad0a8c2d EB	132	} else {
	133	dem->east_scale = 3.0; /* arcseconds */
	134	dem->north_scale = 3.0;
70147e60	135	dem->orig_vert_units = VIK_DEM_VERT_METERS;
ad0a8c2d EB	136	}
	137
	138	/* skip next */
	139	get_double_and_continue(&buffer, &val, TRUE);
	140
	141	/* now we get the four corner points. record the min and max. */
	142	get_double_and_continue(&buffer, &val, TRUE);
	143	dem->min_east = dem->max_east = val;
	144	get_double_and_continue(&buffer, &val, TRUE);
	145	dem->min_north = dem->max_north = val;
	146
	147	for ( i = 0; i < 3; i++ ) {
	148	get_double_and_continue(&buffer, &val, TRUE);
	149	if ( val < dem->min_east ) dem->min_east = val;
	150	if ( val > dem->max_east ) dem->max_east = val;
	151	get_double_and_continue(&buffer, &val, TRUE);
	152	if ( val < dem->min_north ) dem->min_north = val;
	153	if ( val > dem->max_north ) dem->max_north = val;
	154	}
	155
	156	return TRUE;
	157	}
	158
	159	static void dem_parse_block_as_cont ( gchar buffer, VikDEM dem, gint cur_column, gint cur_row )
	160	{
	161	gint tmp;
	162	while ( cur_row < GET_COLUMN(dem, cur_column)->n_points ) {
70147e60 EB	163	if ( get_int_and_continue(&buffer, &tmp,FALSE) ) {
	164	if ( dem->orig_vert_units == VIK_DEM_VERT_DECIMETERS )
	165	GET_COLUMN(dem, cur_column)->points[cur_row] = (gint16) (tmp / 10);
	166	else
	167	GET_COLUMN(dem, cur_column)->points[cur_row] = (gint16) tmp;
	168	} else
ad0a8c2d EB	169	return;
	170	(*cur_row)++;
	171	}
	172	cur_row = -1; / expecting new column */
	173	}
	174
	175	static void dem_parse_block_as_header ( gchar buffer, VikDEM dem, gint cur_column, gint cur_row )
	176	{
	177	guint n_rows;
	178	gint i;
	179	gdouble east_west, south;
	180	gdouble tmp;
	181
	182	/* 1 x n_rows 1 east_west south x x x DATA */
	183
	184	if ( (!get_double_and_continue(&buffer, &tmp, TRUE)) \|\| tmp != 1 ) {
4c77d5e0	185	g_warning(_("Incorrect DEM Class B record: expected 1"));
ad0a8c2d EB	186	return;
	187	}
	188
	189	/* don't need this */
	190	if ( !get_double_and_continue(&buffer, &tmp, TRUE ) ) return;
	191
	192	/* n_rows */
	193	if ( !get_double_and_continue(&buffer, &tmp, TRUE ) )
	194	return;
	195	n_rows = (guint) tmp;
	196
	197	if ( (!get_double_and_continue(&buffer, &tmp, TRUE)) \|\| tmp != 1 ) {
4c77d5e0	198	g_warning(_("Incorrect DEM Class B record: expected 1"));
ad0a8c2d EB	199	return;
	200	}
	201
	202	if ( !get_double_and_continue(&buffer, &east_west, TRUE) )
	203	return;
	204	if ( !get_double_and_continue(&buffer, &south, TRUE) )
	205	return;
	206
	207	/* next three things we don't need */
	208	if ( !get_double_and_continue(&buffer, &tmp, TRUE)) return;
	209	if ( !get_double_and_continue(&buffer, &tmp, TRUE)) return;
	210	if ( !get_double_and_continue(&buffer, &tmp, TRUE)) return;
	211
	212
	213	dem->n_columns ++;
	214	(*cur_column) ++;
	215
	216	/* empty spaces for things before that were skipped */
	217	(*cur_row) = (south - dem->min_north) / dem->north_scale;
	218	if ( south > dem->max_north \|\| (*cur_row) < 0 )
	219	(*cur_row) = 0;
	220
	221	n_rows += *cur_row;
	222
	223	g_ptr_array_add ( dem->columns, g_malloc(sizeof(VikDEMColumn)) );
	224	GET_COLUMN(dem,*cur_column)->east_west = east_west;
	225	GET_COLUMN(dem,*cur_column)->south = south;
	226	GET_COLUMN(dem,*cur_column)->n_points = n_rows;
	227	GET_COLUMN(dem,cur_column)->points = g_malloc(sizeof(gint16)n_rows);
	228
	229	/* no information for things before that */
	230	for ( i = 0; i < (*cur_row); i++ )
	231	GET_COLUMN(dem,*cur_column)->points[i] = VIK_DEM_INVALID_ELEVATION;
	232
	233	/* now just continue */
	234	dem_parse_block_as_cont ( buffer, dem, cur_column, cur_row );
	235
	236
	237	}
	238
	239	static void dem_parse_block ( gchar buffer, VikDEM dem, gint cur_column, gint cur_row )
	240	{
	241	/* if haven't read anything or have read all items in a columns and are expecting a new column */
	242	if ( cur_column == -1 \|\| cur_row == -1 ) {
	243	dem_parse_block_as_header(buffer, dem, cur_column, cur_row);
	244	} else {
	245	dem_parse_block_as_cont(buffer, dem, cur_column, cur_row);
	246	}
	247	}
	248
46e4fa54 QT	249	/* return size of unzip data or 0 if failed */
	250	/* can be made generic to uncompress zip, gzip, bzip2 data */
	251	static guint uncompress_data(void uncompressed_buffer, guint uncompressed_size, void compressed_data, guint compressed_size)
	252	{
	253	z_stream stream;
	254	int err;
	255
	256	stream.next_in = compressed_data;
	257	stream.avail_in = compressed_size;
	258	stream.next_out = uncompressed_buffer;
	259	stream.avail_out = uncompressed_size;
	260	stream.zalloc = (alloc_func)0;
	261	stream.zfree = (free_func)0;
	262	stream.opaque = (voidpf)0;
	263
	264	/* negative windowBits to inflateInit2 means "no header" */
	265	if ((err = inflateInit2(&stream, -MAX_WBITS)) != Z_OK) {
	266	g_warning("%s(): inflateInit2 failed", __PRETTY_FUNCTION__);
	267	return 0;
	268	}
	269
	270	err = inflate(&stream, Z_FINISH);
	271	if ((err != Z_OK) && (err != Z_STREAM_END) && stream.msg) {
	272	g_warning("%s() inflate failed err=%d \"%s\"", __PRETTY_FUNCTION__, err, stream.msg == NULL ? "unknown" : stream.msg);
	273	inflateEnd(&stream);
	274	return 0;
	275	}
	276
	277	inflateEnd(&stream);
	278	return(stream.total_out);
	279	}
	280
	281	static void unzip_hgt_file(gchar zip_file, gulong *unzip_size)
	282	{
	283	void *unzip_data = NULL;
	284	gchar *zip_data;
	285	struct _lfh {
	286	guint32 sig;
	287	guint16 extract_version;
	288	guint16 flags;
	289	guint16 comp_method;
	290	guint16 time;
	291	guint16 date;
	292	guint32 crc_32;
	293	guint32 compressed_size;
	294	guint32 uncompressed_size;
	295	guint16 filename_len;
	296	guint16 extra_field_len;
	297	} __attribute__ ((__packed__)) *local_file_header = NULL;
	298
	299
	300	local_file_header = (struct _lfh *) zip_file;
	301	if (local_file_header->sig != 0x04034b50) {
4258f4e2	302	g_warning("%s(): wrong format", __PRETTY_FUNCTION__);
46e4fa54 QT	303	g_free(unzip_data);
	304	goto end;
	305	}
	306
	307	zip_data = zip_file + sizeof(struct _lfh) + local_file_header->filename_len + local_file_header->extra_field_len;
	308	unzip_data = g_malloc(local_file_header->uncompressed_size);
	309	gulong uncompressed_size = local_file_header->uncompressed_size;
	310
	311	if (!(*unzip_size = uncompress_data(unzip_data, uncompressed_size, zip_data, local_file_header->compressed_size))) {
	312	g_free(unzip_data);
	313	unzip_data = NULL;
	314	goto end;
	315	}
	316
	317	end:
	318	return(unzip_data);
	319	}
	320
31766324	321	static VikDEM vik_dem_read_srtm_hgt(const gchar file_name, const gchar *basename, gboolean zip)
ad0a8c2d	322	{
ad0a8c2d EB	323	gint i, j;
ad0a8c2d EB	324	VikDEM *dem;
46e4fa54 QT	325	off_t file_size;
46e4fa54 QT	326	gint16 *dem_mem = NULL;
31766324	327	gchar *dem_file = NULL;
46e4fa54 QT	328	const gint num_rows_3sec = 1201;
	329	const gint num_rows_1sec = 3601;
	330	gint num_rows;
31766324	331	GMappedFile *mf;
46e4fa54	332	gint arcsec;
a95be497	333	GError *error = NULL;
ad0a8c2d EB	334
	335	dem = g_malloc(sizeof(VikDEM));
	336
	337	dem->horiz_units = VIK_DEM_HORIZ_LL_ARCSECONDS;
70147e60	338	dem->orig_vert_units = VIK_DEM_VERT_DECIMETERS;
ad0a8c2d EB	339
	340	/* TODO */
	341	dem->min_north = atoi(basename+1) * 3600;
	342	dem->min_east = atoi(basename+4) * 3600;
	343	if ( basename[0] == 'S' )
	344	dem->min_north = - dem->min_north;
	345	if ( basename[3] == 'W' )
	346	dem->min_east = - dem->min_east;
	347
	348	dem->max_north = 3600 + dem->min_north;
	349	dem->max_east = 3600 + dem->min_east;
	350
	351	dem->columns = g_ptr_array_new();
	352	dem->n_columns = 0;
	353
a95be497 GB	354	if ((mf = g_mapped_file_new(file_name, FALSE, &error)) == NULL) {
	355	g_error(_("Couldn't map file %s: %s"), file_name, error->message);
	356	g_error_free(error);
31766324 MA	357	g_free(dem);
	358	return NULL;
	359	}
	360	file_size = g_mapped_file_get_length(mf);
	361	dem_file = g_mapped_file_get_contents(mf);
	362
46e4fa54 QT	363	if (zip) {
	364	void *unzip_mem = NULL;
	365	gulong ucsize;
	366
31766324 MA	367	if ((unzip_mem = unzip_hgt_file(dem_file, &ucsize)) == NULL) {
31766324 MA	368	g_mapped_file_free(mf);
46e4fa54 QT	369	g_ptr_array_free(dem->columns, TRUE);
	370	g_free(dem);
	371	return NULL;
	372	}
	373
	374	dem_mem = unzip_mem;
	375	file_size = ucsize;
	376	}
	377
	378	if (file_size == (num_rows_3sec * num_rows_3sec * sizeof(gint16)))
	379	arcsec = 3;
	380	else if (file_size == (num_rows_1sec * num_rows_1sec * sizeof(gint16)))
	381	arcsec = 1;
	382	else {
4258f4e2	383	g_warning("%s(): file %s does not have right size", __PRETTY_FUNCTION__, basename);
31766324	384	g_mapped_file_free(mf);
46e4fa54 QT	385	g_free(dem);
	386	return NULL;
	387	}
	388
	389	num_rows = (arcsec == 3) ? num_rows_3sec : num_rows_1sec;
	390	dem->east_scale = dem->north_scale = arcsec;
	391
	392	for ( i = 0; i < num_rows; i++ ) {
ad0a8c2d EB	393	dem->n_columns++;
ad0a8c2d EB	394	g_ptr_array_add ( dem->columns, g_malloc(sizeof(VikDEMColumn)) );
46e4fa54	395	GET_COLUMN(dem,i)->east_west = dem->min_east + arcsec*i;
ad0a8c2d	396	GET_COLUMN(dem,i)->south = dem->min_north;
46e4fa54 QT	397	GET_COLUMN(dem,i)->n_points = num_rows;
46e4fa54 QT	398	GET_COLUMN(dem,i)->points = g_malloc(sizeof(gint16)*num_rows);
ad0a8c2d EB	399	}
ad0a8c2d EB	400
46e4fa54 QT	401	int ent = 0;
	402	for ( i = (num_rows - 1); i >= 0; i-- ) {
	403	for ( j = 0; j < num_rows; j++ ) {
792a7488 QT	404	GET_COLUMN(dem,j)->points[i] = GINT16_FROM_BE(dem_mem[ent]);
792a7488 QT	405	ent++;
ad0a8c2d EB	406	}
	407
	408	}
	409
46e4fa54 QT	410	if (zip)
46e4fa54 QT	411	g_free(dem_mem);
31766324	412	g_mapped_file_free(mf);
ad0a8c2d EB	413	return dem;
	414	}
	415
	416	#define IS_SRTM_HGT(fn) (strlen((fn))==11 && (fn)[7]=='.' && (fn)[8]=='h' && (fn)[9]=='g' && (fn)[10]=='t' && ((fn)[0]=='N' \|\| (fn)[0]=='S') && ((fn)[3]=='E' \|\| (fn)[3]=='W'))
	417
	418	VikDEM vik_dem_new_from_file(const gchar file)
	419	{
31766324	420	FILE *f=NULL;
ad0a8c2d EB	421	VikDEM *rv;
	422	gchar buffer[DEM_BLOCK_SIZE+1];
	423
	424	/* use to record state for dem_parse_block */
	425	gint cur_column = -1;
	426	gint cur_row = -1;
	427	const gchar *basename = a_file_basename(file);
	428
31766324	429	if ( g_access ( file, R_OK ) != 0 )
ad0a8c2d EB	430	return NULL;
ad0a8c2d EB	431
46e4fa54 QT	432	if ( (strlen(basename)==11 \|\| ((strlen(basename) == 15) && (basename[11] == '.' && basename[12] == 'z' && basename[13] == 'i' && basename[14] == 'p'))) &&
46e4fa54 QT	433	basename[7]=='.' && basename[8]=='h' && basename[9]=='g' && basename[10]=='t' &&
2dc9ab5e	434	(basename[0] == 'N' \|\| basename[0] == 'S') && (basename[3] == 'E' \|\| basename[3] =='W')) {
46e4fa54	435	gboolean is_zip_file = (strlen(basename) == 15);
31766324	436	rv = vik_dem_read_srtm_hgt(file, basename, is_zip_file);
2dc9ab5e QT	437	return(rv);
2dc9ab5e QT	438	}
ad0a8c2d EB	439
	440	/* Create Structure */
	441	rv = g_malloc(sizeof(VikDEM));
	442
	443	/* Header */
31766324	444	f = g_fopen(file, "r");
3b36279c JJ	445	if ( !f ) {
3b36279c JJ	446	g_free ( rv );
31766324	447	return NULL;
3b36279c	448	}
ad0a8c2d EB	449	buffer[fread(buffer, 1, DEM_BLOCK_SIZE, f)] = '\0';
	450	if ( ! dem_parse_header ( buffer, rv ) ) {
	451	g_free ( rv );
	452	return NULL;
	453	}
	454	/* TODO: actually use header -- i.e. GET # OF COLUMNS EXPECTED */
	455
	456	rv->columns = g_ptr_array_new();
	457	rv->n_columns = 0;
	458
	459	/* Column -- Data */
	460	while (! feof(f) ) {
	461	gchar *tmp;
	462
	463	/* read block */
	464	buffer[fread(buffer, 1, DEM_BLOCK_SIZE, f)] = '\0';
	465
	466	/* Fix Fortran-style exponentiation */
	467	tmp = buffer;
	468	while (*tmp) {
	469	if ( *tmp=='D')
	470	*tmp='E';
	471	tmp++;
	472	}
	473
	474	dem_parse_block(buffer, rv, &cur_column, &cur_row);
	475	}
	476
	477	/* TODO - class C records (right now says 'Invalid' and dies) */
	478
	479	fclose(f);
8c060406	480	f = NULL;
ad0a8c2d EB	481
	482	/* 24k scale */
	483	if ( rv->horiz_units == VIK_DEM_HORIZ_UTM_METERS && rv->n_columns >= 2 )
	484	rv->north_scale = rv->east_scale = GET_COLUMN(rv, 1)->east_west - GET_COLUMN(rv,0)->east_west;
	485
	486	/* FIXME bug in 10m DEM's */
	487	if ( rv->horiz_units == VIK_DEM_HORIZ_UTM_METERS && rv->north_scale == 10 ) {
	488	rv->min_east -= 100;
	489	rv->min_north += 200;
	490	}
	491
	492
	493	return rv;
	494	}
	495
	496	void vik_dem_free ( VikDEM *dem )
	497	{
	498	guint i;
	499	for ( i = 0; i < dem->n_columns; i++)
	500	g_free ( GET_COLUMN(dem, i)->points );
	501	g_ptr_array_free ( dem->columns, TRUE );
	502	g_free ( dem );
	503	}
	504
	505	gint16 vik_dem_get_xy ( VikDEM *dem, guint col, guint row )
	506	{
	507	if ( col < dem->n_columns )
	508	if ( row < GET_COLUMN(dem, col)->n_points )
	509	return GET_COLUMN(dem, col)->points[row];
	510	return VIK_DEM_INVALID_ELEVATION;
	511	}
	512
	513	gint16 vik_dem_get_east_north ( VikDEM *dem, gdouble east, gdouble north )
	514	{
	515	gint col, row;
	516
	517	if ( east > dem->max_east \|\| east < dem->min_east \|\|
	518	north > dem->max_north \|\| north < dem->min_north )
	519	return VIK_DEM_INVALID_ELEVATION;
	520
	521	col = (gint) floor((east - dem->min_east) / dem->east_scale);
	522	row = (gint) floor((north - dem->min_north) / dem->north_scale);
	523
	524	return vik_dem_get_xy ( dem, col, row );
	525	}
	526
5ef1d57e QT	527	static gboolean dem_get_ref_points_elev_dist(VikDEM *dem,
	528	gdouble east, gdouble north, /* in seconds */
	529	gint16 elevs, gint16 dists)
	530	{
	531	int i;
	532	int cols[4], rows[4];
	533	struct LatLon ll[4];
	534	struct LatLon pos;
	535
	536	if ( east > dem->max_east \|\| east < dem->min_east \|\|
	537	north > dem->max_north \|\| north < dem->min_north )
	538	return FALSE; /* got nothing */
	539
	540	pos.lon = east/3600;
	541	pos.lat = north/3600;
	542
	543	/* order of the data: sw, nw, ne, se */
245575e1 QT	544	/* sw */
245575e1 QT	545	cols[0] = (gint) floor((east - dem->min_east) / dem->east_scale);
5ef1d57e	546	rows[0] = (gint) floor((north - dem->min_north) / dem->north_scale);
228213c5 QT	547	ll[0].lon = (dem->min_east + dem->east_scale*cols[0])/3600;
228213c5 QT	548	ll[0].lat = (dem->min_north + dem->north_scale*rows[0])/3600;
245575e1 QT	549	/* nw */
245575e1 QT	550	cols[1] = cols[0];
5ef1d57e QT	551	rows[1] = rows[0] + 1;
	552	ll[1].lon = ll[0].lon;
	553	ll[1].lat = ll[0].lat + (gdouble)dem->north_scale/3600;
245575e1 QT	554	/* ne */
245575e1 QT	555	cols[2] = cols[0] + 1;
5ef1d57e QT	556	rows[2] = rows[0] + 1;
	557	ll[2].lon = ll[0].lon + (gdouble)dem->east_scale/3600;
	558	ll[2].lat = ll[0].lat + (gdouble)dem->north_scale/3600;
245575e1 QT	559	/* se */
245575e1 QT	560	cols[3] = cols[0] + 1;
5ef1d57e QT	561	rows[3] = rows[0];
	562	ll[3].lon = ll[0].lon + (gdouble)dem->east_scale/3600;
	563	ll[3].lat = ll[0].lat;
	564
	565	for (i = 0; i < 4; i++) {
	566	if ((elevs[i] = vik_dem_get_xy(dem, cols[i], rows[i])) == VIK_DEM_INVALID_ELEVATION)
	567	return FALSE;
	568	dists[i] = a_coords_latlon_diff(&pos, &ll[i]);
	569	}
	570
228213c5 QT	571	#if 0 /* debug */
	572	for (i = 0; i < 4; i++)
	573	fprintf(stderr, "%f:%f:%d:%d ", ll[i].lat, ll[i].lon, dists[i], elevs[i]);
	574	fprintf(stderr, " north_scale=%f\n", dem->north_scale);
	575	#endif
	576
5ef1d57e QT	577	return TRUE; /* all OK */
	578	}
	579
	580	gint16 vik_dem_get_simple_interpol ( VikDEM *dem, gdouble east, gdouble north )
	581	{
	582	int i;
	583	gint16 elevs[4], dists[4];
	584
	585	if (!dem_get_ref_points_elev_dist(dem, east, north, elevs, dists))
	586	return VIK_DEM_INVALID_ELEVATION;
	587
	588	for (i = 0; i < 4; i++) {
	589	if (dists[i] < 1) {
	590	return(elevs[i]);
	591	}
	592	}
	593
	594	gdouble t = (gdouble)elevs[0]/dists[0] + (gdouble)elevs[1]/dists[1] + (gdouble)elevs[2]/dists[2] + (gdouble)elevs[3]/dists[3];
	595	gdouble b = 1.0/dists[0] + 1.0/dists[1] + 1.0/dists[2] + 1.0/dists[3];
	596
	597	return(t/b);
	598	}
	599
	600	gint16 vik_dem_get_shepard_interpol ( VikDEM *dem, gdouble east, gdouble north )
	601	{
228213c5 QT	602	int i;
	603	gint16 elevs[4], dists[4];
	604	gint16 max_dist;
	605	gdouble t = 0.0;
	606	gdouble b = 0.0;
	607
	608	if (!dem_get_ref_points_elev_dist(dem, east, north, elevs, dists))
	609	return VIK_DEM_INVALID_ELEVATION;
	610
	611	max_dist = 0;
	612	for (i = 0; i < 4; i++) {
	613	if (dists[i] < 1) {
	614	return(elevs[i]);
	615	}
	616	if (dists[i] > max_dist)
	617	max_dist = dists[i];
	618	}
	619
	620	gdouble tmp;
	621	#if 0 /* derived method by Franke & Nielson. Does not seem to work too well here */
	622	for (i = 0; i < 4; i++) {
	623	tmp = pow((1.0(max_dist - dists[i])/max_distdists[i]), 2);
	624	t += tmp*elevs[i];
	625	b += tmp;
	626	}
	627	#endif
	628
	629	for (i = 0; i < 4; i++) {
	630	tmp = pow((1.0/dists[i]), 2);
	631	t += tmp*elevs[i];
	632	b += tmp;
	633	}
	634
	635	// fprintf(stderr, "DEBUG: tmp=%f t=%f b=%f %f\n", tmp, t, b, t/b);
	636
	637	return(t/b);
	638
5ef1d57e QT	639	}
5ef1d57e QT	640
ad0a8c2d EB	641	void vik_dem_east_north_to_xy ( VikDEM dem, gdouble east, gdouble north, guint col, guint *row )
	642	{
	643	*col = (gint) floor((east - dem->min_east) / dem->east_scale);
	644	*row = (gint) floor((north - dem->min_north) / dem->north_scale);
	645	if ( col < 0 ) col = 0;
	646	if ( row < 0 ) row = 0;
	647	}
	648