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Dash Express

Issue 176

From Issue #176
December 2008

Dec 01, 2008  By Kyle Rankin
 in
You are always on the Internet, so why shouldn't your GPS be? Read on for a review of the Dash Express GPRS-connected GPS system.
Developing Dash Apps

Earlier in the year, the Dash opened up its API to the community, so anyone could register on its site as a developer and write custom Dash apps. Since then, the API has been updated and expanded with some new features, and it still appears to be in active development. Even so, there already seems to be a pretty active developer community springing up in the Dash forums, and quite a few community-developed Dash apps are already available on the site.

I wanted to see how easy it was to develop my own Dash app, so I downloaded the latest edition of the API documentation, registered as a developer on the site, and started with a sample PHP program I found on the forum. Essentially, when you conduct a search with a Dash app, the Dash Express then sends an HTTP GET to a Web service you specify that contains a few variables including the Dash's GPS location and potentially a custom value from a text entry window on the Dash itself. Your Web service replies back with its results formatted in some basic XML (the structure is defined in the API documentation) that the Dash then displays. Here's a sample of the XML output that Dash accepts: 


<?xml version="1.0" encoding="UTF-8"?>
<resultSet><serviceId>10114</serviceId><count>1</count>
<sort>di</sort>
<result><title>Title</title>
<point>38.2440154167-122.6531425</point>
<description>requestType->search   serviceId->10114
point->38.24401541666667 -122.6531425   count->20   
offset->0   sort->null signature->ed002f9a2f86013c9affd8d9e1b9f90e   
</description><address>12000 San Jose
Blvd</address><city>Jacksonville</city>
<regionCode>FL</regionCode><countryCode>US</countryCode>
<postalCode>32223</postalCode></result></resultSet>

After all these years, I still tend to favor Perl for this sort of thing, so the first thing I did was port the sample PHP script to Perl. Once I got that working, I decided to try to write something actually useful. I wasn't ready to dig heavily into sourcing sites like Google Maps for location data, so instead, I decided to write something more basic. I planned to write an application that would take the current mileage as input and then read from a basic CSV file and report back any maintenance due within plus or minus 10,000 miles. The first column in the CSV file has the mileage when the maintenance was due, the second column has a description of the maintenance, and the third column is optional but had a 1 or 0 depending on whether the task was completed. Here's some sample lines from the file: 

151000,Change Oil,1
156000,Change Oil and Filter,1
161000,Change Oil
160000,Replace Tires
180000,Replace Coolant
160000,Replace Air Filter

Listing 1 shows the script that reads from the file and outputs the XML for the Dash.

Listing 1. The Script

#!/usr/bin/perl

use CGI qw(:standard);

my $infile = 'maintenance.txt';
my $mileage_range = "10000"; # Only show entries within this range

if(param())
{
   $requestType = param("requestType");
   $serviceId = param("serviceId");
   $point = param("point");
   $count = param("count");
   $offset = param("offset");
   $sort = param("sort");
   $signature = param("signature");
   $mileage = param("q");
   my %hash;
   my $items = 0;

   parse_infile($infile, \%hash);

   foreach (sort keys %hash){
      if(abs($_ - $mileage) < $mileage_range){
	 next if($hash{$_}{'c'} == 1);

	 $delta = $_ - $mileage;
	 if($delta >= 0){
	    $title = "$_ - $hash{$_}{'desc'}";
	    $desc = "<![CDATA[<html>In <b>$delta</b>
 ↪miles:<br>$hash{$_}{'desc'}</html>]]>";
	 }
	 else {
	    $title = "PAST DUE: $hash{$_}{'desc'}";
	    $desc = "<![CDATA[<html><font color=#FF0000>
  ↪<b>" . abs($delta) . "</b> miles <i>PAST DUE</i>
  ↪</font>:<br>$hash{$_}{'desc'}</html>]]>";
	 }

	 $output .= output_result($title, $desc);
	 $items++;
      }
   }

   print header('text/xml');
   print '<?xml version="1.0" encoding="UTF-8"?>'
            . "\n<resultSet>"
            . "<serviceId>$serviceId</serviceId>"
            . "<count>$items</count>";

   print $output;
   print '</resultSet>';
   exit;
}

sub output_result {
   my $title = shift;
   my $desc = shift;
   my $output;

   $output =  "\n<result>"
            . "<title>$title</title>"
            . "<description>$desc</description>"
            . '</result>';

   return $output;
}

sub parse_infile {
   my $infile = shift;
   my $href = shift;
   my ($mileage, $desc, $completed);

   open INFILE, $infile or die "Can't open $infile: $!\n";
   while(<INFILE>){
      chomp;
      $mileage = $desc = $completed = "";
      ($mileage, $desc, $completed) = split ',', $_;
      $$href{$mileage}{'desc'} = $desc;
      $$href{$mileage}{'c'} = $completed;
   }
   close INFILE;
}

It's pretty basic, but it works. The whole process from testing the PHP script to writing the final application took only about two hours. Once you write the program, you can create a new Dash app instance via an interface on the my.dash.net site and add it to your saved searches. You also can choose to keep the program to yourself, or you can make it public so any Dash user can use it.

The ease of developing applications for the Dash is a definite plus for me. There are still some limitations in its API (for instance, there is only one text box available for user entry at the time of this writing), but the API still appears to be under heavy development and already has had feature updates. Even as it is, if you have some imagination and some programming ability, you can write some pretty useful applications.

______________________

Kyle Rankin is a systems architect; and the author of DevOps Troubleshooting, The Official Ubuntu Server Book, Knoppix Hacks, Knoppix Pocket Reference, Linux Multimedia Hacks, and Ubuntu Hacks.

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Unfortunately...

kendricbeachey's picture
Submitted by kendricbeachey on Mon, 11/24/2008 - 20:47.

Unfortunately, Dash just got out of the hardware biz.

http://www.bizjournals.com/sanjose/stories/2008/11/03/daily29.html

There are still other Linux-based GPS devices out there although none that are quite as hackable.

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