taking GDAL/OGR ruby bindings for a spin

Since i have volunteered to write the gdal ruby-binding test cases i thought it would be a good time to try out some of the ogr ruby-bindings. Charlie Savage has done a lot of work on the gdal SWIG ruby biniding and already written the test suite for OGR. Thanks to his excellent instructions on how to get started with writing the gdal-ruby test suit i was able to to easily convert Ari Jolma’s dumpall.pl to a ruby script to dump the contents of ogr (Vector) datastore.

require 'gdal/ogr'
 
@global_extent = Array.new#(4, 0.0)
 
def dump_geom(geom, v)
  print "  Geometry type: ", geom.get_geometry_type, "\n"
  print "  Geometry name: ", geom.get_geometry_name, "\n" 
  extent = geom.get_envelope
  print "  BBox: ", extent[0], " ", extent[2], " ", extent[1], " ", extent[3], "\n" 
  for i in [0, 2]
    if (@global_extent[i].nil?) or @global_extent[i] > extent[i]
      @global_extent[i] = extent[i] 
    end
  end
  for i in [1, 3]
    if (@global_extent[i].nil?) or @global_extent[i] < extent[i]
      @global_extent[i] = extent[i] 
    end
  end
  if (geom.get_geometry_count > 0) 
    print "Geom Count = ", geom.get_geometry_count, "\n"
    geom.get_geometry_count.times do |i|
      dump_geom(geom.get_geometry_ref(i),v)
    end
  else
    if(!v)
      print "PointCount: ", geom.get_point_count,"\n" 
      geom.get_point_count.time do |i| 
      x = geom.get_x(i)
      y = geom.get_y(i)
      z = geom.get_x(i)
      print  " ",  x, " ", y, " ", z, "\n";
      end 
    end
  end
end
 
def dump_feature_data(feature, layer)
  feature_defn = layer.get_layer_defn  
  print "Feature ID: ", feature.get_fid, "\n"
  feature_defn.get_field_count.times do |i|
    print "Field ", i+1, "\n"
    field_defn = feature_defn.get_field_defn(i)
    print "  Field name: ",field_defn.get_name_ref,"\n" 
    type = field_defn.get_type
    print "  Field type: ", field_defn.get_field_type_name(type)," type\n"
    field = feature.get_field_as_string(i);
    print "  Field value: ", field,"\n"
  end
end
 
def dump_layer(layer)
  layer.reset_reading
  layer.get_feature_count.times do |i|
    feature = layer.get_feature(i)
    dump_feature_data(feature, layer)
    geom = feature.get_geometry_ref()
    do_not_show_vertices = 1
    if not geom.nil?
      dump_geom(geom, do_not_show_vertices)
    elsif geom.nil?
      print "*** expected geometry but got nill\n"
    end
end
end
 
if ARGV.length < 1
  print "Usage:  #$0", " <input_file>\n"
  exit
else
  filename = ARGV[0]
end
# driver = Gdal::Ogr.get_driver_by_name('ESRI Shapefile')
# open file as a OGR dataset
dataset = Gdal::Ogr.open(filename)
print "Looking at ", filename + " ...\n"
# get the number of layers
layer_num = dataset.get_layer_count 
layer_num.times do |i|
  layer = dataset.get_layer(i)  
  print "  looking at layer num: ", i+1 , "\n",
  "  Name: "+layer.get_name + ", Features: "+ layer.get_feature_count.to_s + "\n"
  dump_layer(layer)
end
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  • shoaib
    Sadly there is no documentation for the ruby bindings and infact they are not being actively maintained. When I work with them it usually involves diving into the C/C++ sources. However I would like to start documenting the API for the gdal/ogr bindings.

    For your immediate needs of manipulating a shapefile have a look at GeoRuby which has tools for reading/writing shapefiles, eg.:
    http://georuby.rubyforge.org/svn/GeoRuby/trunk/tools/shp2sql.rb
  • Jan
    Hi,

    I am trying to use this library on one of my project. I would love to locate the sources and at least generate documentation for them. Using this API without any sense of what which method expects as parameters is rather no funny.

    Thanks for any response!
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