#!/usr/bin/perl
# filename: makesurf.pl
# author:   Marvin Simkin
# date:     2002-11-17
# purpose:  read Garmin Mapsource output make road lines

# syntax:   makesurf.pl < bed.surf > bed.draw
# bed.surf: some surface data produced e.g. by GMT "surface" command
# bed.draw: object drawing instructions for makeiv.pl

# NOTE:
# Input data format:
# 463114{t}896228{t}860.646
# 463200{t}896228{t}862.11
# 463285{t}896228{t}863.574
# 463371{t}896228{t}865.038
# 463456{t}896228{t}866.501
# 463542{t}896228{t}867.962
# 463627{t}896228{t}869.422
# 463713{t}896228{t}870.879
# 463798{t}896228{t}872.333
# 463884{t}896228{t}873.782
#
# Data should be ordered with X varying fastest and repeatedly,
# with one sequential pass through Y.
#
# Gridded data varies by X while Y remains constant,
# for the first pass through the grid.
# Then X starts over with the next Y.
# This program makes triangles connecting the grid points
# to create a solid VRML 1.0 surface (after conversion with makeiv.pl).
#
# This assumes the X values are the same for every pass
# though it could probably be modified to handle other cases.


# Output data format
# triangle:X1,Y1,Z1,X2,Y2,Z2,X3,Y3,Z3

# INITIALIZE:

my @Column;

my $LastX;
$LastX = '';

my $LastY;
$LastY = '';

my $ThisY;
$ThisY = '';

my %LastZ;
my $SaveZ;


# SUBROUTINES:
use strict;


# ARGUMENTS:


# MAINLINE:
my $Line;
while ($Line = <>) {
  chomp $Line;

  @Column = split (' ', $Line);

  # don't bother with too-short lines
  if ($#Column > 1) {
    my $X;
    my $Y;
    my $Z;

    $X = $Column[0];
    $Y = $Column[1];
    $Z = $Column[2];

    if ($Y eq $ThisY) {
      # continue with same row

      # if this is the first row we can't draw triangles yet
      if ($LastY ne '') {
        # draw a pair of triangles on one line since they go together
#ENH# could set color (or delete entirely) depending on surface grid accuracy
#ENH# or possibly even pick up a pixel from a same-gridded image?
        print "triangle:$LastX,$LastY,$SaveZ,$LastX,$ThisY,$LastZ{$LastX},$X,$Y,$Z;";
        print "triangle:$LastX,$LastY,$SaveZ,$X,$LastY,$LastZ{$X},$X,$Y,$Z\n";

      }

    } else {
      # starting a new row
      $LastY = $ThisY;
      $ThisY = $Y;

      # since this is the first point on this row we can't draw triangles

    }

    # save remembered point before we overwrite it
    $SaveZ = $LastZ{$X};

    # save incoming point for next pass
    $LastZ{$X} = $Z;
    $LastX = $X;

  } else {
    print STDERR "Skipped line without 3 columns of data: '$Line'\n";
  }
}