ply¶ ↑

github.com/jimwise/ply

Author

Jim Wise (jwise@draga.com)

Copyright

Copyright © 2013 Jim Wise

License

2-clause BSD-Style (see LICENSE.txt)

Ply is a ruby gem for reading Stanford PLY-format 3D model files.

The PLY file format is a flexible format for storing semi-structured binary data, and is often used to stored polygonalized 3D models generated with range scanning hardware. You can find some examples of the format at the Stanford 3D Scanning Repository.

Ply provides a simple API for quick access to the data in a PLY file (including examining the structure of a particular file’s content), and an almost-as-simple event-driven API which can be used to process extremely large ply files in a streaming fashion, without needing to keep the full dataset represented in the file in memory. Ply handles all three types of PLY files (ascii, binary-big-endian and binary-little-endian).

If you don’t have any Stanford PLY files on hand, you probably don’t need this gem, but if you’re curious, the PLY file format is described at Wikipedia.

Ply currently requires Ruby 1.9.3 – if you have a need to run Ply with Ruby 1.8.7, drop me an email, and I’ll look into backporting it. Ply has no other dependencies.

$ gem install ply

To get started, include this gem using

require 'ply'

This gem provides the Ply module. This module provides a single class, Ply::PlyFile, which can be used directly to parse a PLY file into memory, or subclassed to take advantage of Ply’s event-driven API for handling large PLY files.

To parse a PLY file into memory, simply instantiate the Ply::PlyFile class, passing either the name of the PLY file or an IO object open on a PLY file to Ply::PlyFile.new. Thus this:

pf = Ply::PlyFile.new "horse.ply"

and this:

pf = Ply::PlyFile.new File.new("horse.ply")

do the same thing.

The PLY file is parsed at construction time, and provides the following read-only accessors:

Ply::PlyFile#version

The version of the PLY format used in this file, as a String – at this time the only defined PLY version is 1.0.

Ply::PlyFile#format

The format of this PLY file as a String– one of ascii, binary_big_endian, or binary_little_endian.

Ply::PlyFile#elements

The structure of the data in this PLY file, as an array of Hashes, in the order the elements will appear in the file. Each Hash contains the following keys:

:name

the name of this element type

:count

the number of elements of this type in this PLY file

:properties

an array of Hashes describing the properties of this element type. Each Hash in the :properties array contains the following keys:

:name

the name of this property of the current element

:type

the type of this property (an integral or floating point type, as defined in the PLY file format, or list. If the current property is of type list (a PLY array type), its property Hash also contains the following keys:

:index_type

the type of the index of this list

:element_type

the type of the elements in this list

If you are using the Ply::PlyFile class directly (as opposed to subclassing it in order to use Ply’s event-driven API for handling large PLY files), an additional read-only accessor is available

Ply::PlyFile#data

The actual data in this file, in the structure defined by the return value of Ply::PlyFile#elements, as a Hash of Arrays of Hashes. This data is returned as a Hash keyed by the name of each element type in the file (as a String), and containing an array of Hashes for each element type in the file, keyed by the property names of that element, as Strings.

That’s not as complicated as it sounds! If the file horse.ply defines a vertex element, with properties x, y, and z, then

pf = Ply::PlyFile.new "horse.ply"
verts = pf.data["vertex"]

will return an array of all vertices in the file, and

verts[0]["x"]

will give you the value of the x property of the first vertex element in the file, as an Integer, Float, or Array, depending on the declared type of that property in the PLY file.

The above API is easy to use, but has the disadvantage that the entire data stored in the PLY file must be able to fit in memory, in order to be returned by Ply::PlyFile::data. For this reason, a simple event-driven API for handling PLY data is also provided. To make use of this, simply subclass the class Ply::PlyFile, and provide your own version of the method Ply::PlyFile#element_callback. When a new object of your subclass is constructed from a PLY file, your implementation of this method will be called once for each element in the file, and passed two arguments:

• The type of the current element, in the same format as a member of the array returned by Ply::PlyFile::elements

• The current element, in the same format as a member of the arrays returned by Ply::PlyFile::data

Note that if your subclass provides a #initialize method, it is your responsibility to ensure that the initialize method of Ply::PlyFile is also called with an appropriate argument – see below for an example of how to do this using ruby’s super keyword.

As an example, the following code defines a subclass of PlyFile which merely counts the elements of each type present in PLY file, without reading them all into memory at the same time:

require 'ply'

class PlyFileCounter < Ply::PlyFile
  attr_reader :counts

  def initialize f
    @counts = {}
    super f
  end

  def element_callback e, v
    @counts[e[:name]] ||= 0
    @counts[e[:name]] = @counts[e[:name]] + 1
  end
end

p = PlyFileCounter.new "horse.ply"
puts "There are #{p.counts["vertex"]} vertices in the file."

In addition to the large models in the Stanford 3D Scanning Repository, the examples/ subdirectory of this gem includes a simple triangulated cube model in all three PLY file formats, as well as a script to generate these three files, which also provides an example of how to write Ply files using ruby.

Finally, this gem includes a simple script, ply2ascii, which can be used to parse any of the three PLY file formats containing a triangulated scene with vertices in an element named vertex with (at least) scalar properties x, y, and z, and faces in an elemnt named face containing a list property vertex_indices, and produce a simple ASCII dump of the described scene in two files.

Run ply2ascii with no arguments for (a little) more information.

After checking out the source, run:

$ rake newb

This task will install any missing dependencies, run the tests/specs, and generate the RDoc.

(The BSD 2-clause License)

Copyright (c) 2013 Jim Wise
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.

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"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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