a more or less open-source aproach to working with GPS sensors using OS X

For this part of the workshop we are going to work with some open-source software and have a look (or a quick glance) at
how a unix system like os x provides a facility for working with this kind of software.

Wikipedia on open-source software

What we are going to do:

• Download and compile gpsd, an open source GPS utility
• Download and install PureData - an open-source environment for sound production.
• make them work together using php, an an open source scripting language

During this exercise, we will mostly work with the Terminal. You can find it under Applications -> Utilities -> Terminal

The terminal is a text interface for working with the operating system as opposed to the clicking on the object that the slick OS X "Aqua" surface provides..

1. Some things to install first....

First you need to make sure, that the Developer Tools from Apple are installed. Check if you have Applications -> Installer -> Xcode Tools (if you don't you have to install them from the operating system CD or DVD).

Then, you need to install the drivers for the gps as mac os x does not have any generic drivers. (drivers for deluo usb gps are here, the drivers for the serial gps are here)

Fink is also a good thing to install if you want to work with open source software on os x. Because you can use the Advanced Packaging Tool Apt for installing Debian (Linux) packages on your Os X machine.

2.Downloading and Installing GPSD

GPSD is an open-source program that provides an interface for getting data from the GPS for use in self-made programs.

• Point your browser to http://gpsd.berlios.de/
• download GPSD gpsd-1.98.tar.gz to your Applications Folder (the ending tar means that the folder is an archive file and the .gz ending means that it is compressed). means that the files are compressed)
• launch the terminal and unpack GPSD using the following commands
  cd /Volumes/MacintoshHD/Applications/ (cd means "change directory" - so you are now changing into the directory (or folder) called "Applications".
  ls (this lists all the files in that directory)
• tar -xzf gpsd-1.89.tar.gz (this uncompresses the files).
• if you now do "ls" again, you will find a new directory in you "Applications" folder.
  
  
  

So we have uncompressed the GPSD directory. It contains all the files that we need to compile the gpsd program. This is how you do it:

 
• cd gpsd-1.98
  now you are in the gpsd directory. You can then type "ls" to look at the files that are contained in this directory. Now type
• sudo ./configure (this will check if all things needed to compile the sources is on the computer)
• sudo make (this will compile the sources)

The reason why we are using sudo is that in order compile a program you need more permissions than the average user. Sudo gives you the administrator permissions.

if everything worked out, we can now connect the GPS and check if the program functions...

if it did not compile for some weird reason, you can download the folder with the compiled gpsd here: gpsd_compiled.tar.gz running this one on a mac should work.

• ./gpsd -h (this will show a help menu that explains how the program is used)
• ./gpsd -p /dev/tty.usbserial0 -s 4800 (now we are starting the program. while starting it we need to give it some parameters. like where to look for the gps-input and at what speed (this is only needed for serial gps' but I just put it anyway 'cause i am superstitious.)
• if nothing happens after you have pressed ENTER, it's a good sign because the program is a deamon and runs in the background. It's kind of like a server that you can contact to get the data.

• type telnet localhost 2947
  

if you type "p" the position (latitude / logitude) is shown
if you type "a" the altitude is shown
if you type "s" the number of located satellites is shown

of course if you are inside, under a bridge or somewhere where there is now sky view, only typing "s" returns anything.

 

3. DOWNLOADING AND INSTALLING THE BINARY VERSION OF PureData (PD)

Point your browser to

Download: Pd version 0.37-2 compiled for Macintosh. You might also need Tcl/TK for Macintosh OSX .

check in /Library/Frameworks if there is anything like tk.framework and/or tcl.framework (if no, you have to download Tcl/TK. To install, doubleclick the .mpkg package and follow the instructions)

now you should be ready to run pd:

in a Shell (Terminal) type: /Applications/pd-0.37-2/bin/pd

or: you can just click the pd file in /Applications/pd-0.37-2/bin/pd

Simple PD examples (download patches & php files here php_pd.tar.gz)

triggering sounds with a delay:

To test sending data to a pd patch test it: echo 'one 1;' | /Applications/pd-0.37-2/bin/pdsend 2345

subpatch: pd gives you the possibility to use an instance of another patch.

in this case the subpatch is the attack_release.pd file.

4. Making a PHP script to connect PD and GPSD

The way to learn PHP: look up functions on www.php.net and somehow put together a script that works.

• Script that queries the satellite
• Script that queries for satellite connection and a pd-patch that makes sound

(picture below)





• Script that queries for satellite connection & gps coordinates and pd-patch that makes sound (picture below).
•