Setting up a C++ Development Environment for Computer Vision

This document describes how to setup a C++ development environment for computer vision work.

Overview of Technologies

• Virtual Machine
• Virtual Box - Similar in purpose to VMWare or Xen.
• Vagrant - An easy way to configure manage virtual machines in a reproducible manner.
• C++ Libraries
• Boost - Portable reasonable quality libraries.
• OpenCV
• Thrift - Facebook's cross-language RPC framework.
• SEBS/Blaze - Build system similar in appearance to Google's Blaze.

Prerequisites

You need to install Virtual Box. If you are using OS X or Windows there are packages for you. There is also probably a package for your Linux distribution.

You also need to install Vagrant, there are several packages here.

Downloading the VM

The time to compile and configure (even though it is scripted) the environment is not insignificant. So I have provided an image with everything installed.

Navigate to the vm directory and run:

wget http://94.23.6.172/precise64-v1.box
vagrant box add precise64-v1 precise64-v1.box
rm precise64-v1.box

Now let's boot up the virtual machine:

vagrant up
[default] Importing base box 'precise64-v1'...
[default] The guest additions on this VM do not match the install version of
VirtualBox! This may cause things such as forwarded ports, shared
folders, and more to not work properly. If any of those things fail on
this machine, please update the guest additions and repackage the
box.

Guest Additions Version: 4.2.0
VirtualBox Version: 4.2.4
[default] Matching MAC address for NAT networking...
[default] Clearing any previously set forwarded ports...
[default] Forwarding ports...
[default] -- 22 => 2222 (adapter 1)
[default] Creating shared folders metadata...
[default] Clearing any previously set network interfaces...
[default] Running any VM customizations...
[default] Booting VM...
[default] Waiting for VM to boot. This can take a few minutes.
[default] VM booted and ready for use!
[default] Mounting shared folders...
[default] -- v-root: /vagrant
[default] -- v-depot: /cvenv/depot
[default] -- v-puppet-files: /etc/puppet/files
[default] -- manifests: /tmp/vagrant-puppet/manifests
[default] Running provisioner: Vagrant::Provisioners::Puppet...
[default] Running Puppet with /tmp/vagrant-puppet/manifests/precise64.pp...
stdin: is not a tty
notice: Scope(Class[main]): Running configure scripts,
this make take a long time for the first boot...
notice: Scope(Class[Users]): Users

info: Applying configuration version '1353361028'
notice: /Stage[main]//Exec[apt-update]/returns: executed successfully
notice: Finished catalog run in 35.62 seconds

If you get an error:

vagrant ssh

The private key to connect to this box via SSH has invalid permissions
set on it. The permissions of the private key should be set to 0600, otherwise SSH will
ignore the key. Vagrant tried to do this automatically for you but failed. Please set the
permissions on the following file to 0600 and then try running this command again:

/Users/stephen/Documents/Projects/cvenv/vm/puppet/files/id_rsa
$ chmod 666 /Users/stephen/Documents/Projects/cvenv/vm/puppet/files/id_rsa

Building Code

SSH into the Virtual Machine:

vagrant ssh

Then

cd /cvenv/depot

And compile

$ blaze build src/examples/hello_world:all
examples/hello_world:hello_world_main
configure: C++ compiler flags -O3 -std=c++0x -Wno-deprecated -I/usr/local/include/ -I/usr/local/include/thrift/ -L/usr/lib -L/usr/local/lib 
configure: C++ compiler g++
*compile: src/examples/hello_world/hello_world_main.cc
compile: src/examples/hello_world/hello_world_main.cc
link: examples/hello_world:hello_world_main

$ ./bin/examples/hello_world/hello_world_main
I1119 20:16:53.429513  1347 hello_world_main.cc:12] Hello world!

Vagrant Commands

• vagrant up - Start the VM
• vagrant halt - Shutdown the VM
• You can also use sudo shutdown -h now from inside the VM.
• vagrant ssh - SSH into the VM.
• vagrant status - Current status of VMs.

RPC Overview

For some computer vision projects, you may want to have a web interface to your C++ code. A common pattern is to have a simple frontend server running a scripting language like Python/PHP/Ruby connect to a backend C++ server.

The servers may be on the same machine or different machines. This pattern creates a nice separation of presentation logic and backend computation.

A common library used for the communication between the backend and frontend pieces is Thrift. Thrift is an Remote Procedure Call (RPC) framework. We can write a server in C++ that performs heavy calculations which we can call from our simple Python application.

Thrift Example

Let's say we have some C++ code which returns search results for a given query. We can define an interface like so:

// Copyright 2012
// Author: Stephen Holiday (stephen.holiday@gmail.com)

namespace cpp examples.searchengine
namespace py examples.searchengine

struct SearchRequest {
  1: string key,
  2: string url
}

struct SearchResult {
  1: string key,
  2: string url,
  3: double score
}

struct SearchResponse {
  1: list<SearchResult> results,
  2: bool success,
  3: string message
}

service SearchEngineService {
  SearchResponse search(1: SearchRequest request)
  i32 ping()
}

Thrift C++ Server

Then the C++ service would look something like this:

class SearchEngineServiceImpl : virtual public SearchEngineServiceIf {
 public:
  SearchEngineServiceImpl() {};
  void search(SearchResponse& response, const SearchRequest& request);
  int32_t ping();
};

Thrift Python Client

# Create a socket to the server.
transport = TSocket.TSocket('localhost', 9001)
# Use a framing transport.
transport = TTransport.TFramedTransport(transport)
# Use a binary protocol.
protocol = TBinaryProtocol.TBinaryProtocol(transport)
# Create the client wrapper.
client = SearchEngineService.Client(protocol)
# Connect to the server.
transport.open()

# Attempt to ping the server.
print "Ping result: %s" % client.ping()

# Create a fake search request.
request = SearchRequest(url="http://example.com/img.png")

# Send the request.
print "Sending request..."
response = client.search(request)
print "Recieved response."

if response.success:
  print "Search was a success!"
else:
  print "Search was a failure."

print "The results are:"
for result in response.results:
    print '(Key: %s, Score: %s)' % (result.key, result.score)

transport.close()