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Although location-based software for mobile devices often centers on the purely commercial, such as finding the

nearest pizza joint, a pair of entrepreneurs based in the United Kingdom and The Netherlands have delivered a more

socially conscious application. Their Carbon Hero software is a personal carbon calculator that ties into

smartphones’ built-in GPS technology, tracks a user’s travels and automatically calculates the resulting CO2

emissions to give an immediate understanding of personal environmental impact.

With the threat of global warming, "people are increasingly interested in their personal carbon use, and how they can

reduce it," says Andreas Zachariah, CEO of Carbon Diem, the company that developed Carbon Hero.

Until now, getting such data meant logging the relevant details and entering them into an online carbon calculator.

But "we are all typically way too busy for that," notes Zachariah.

Figure 1. A graphical example of an R-Tree search looks to see if two lines intersect.

That sparked the idea for Carbon Hero, which rides along in technology already carried by millions of people.

The application now is in field testing on BlackBerry devices, but company co-founders Zachariah and Nick 

Burch, chief technology officer, have deployed it on Nokia phones and plan to add other platforms.

Database Structures

Carbon Hero works via savvy coding in Java ME, the embedded Java technology deployed in billions of mobile devices worldwide.

Its innovation includes custom algorithms that detect transport mode, such as car vs. jet airplane.

In writing the code that enables Carbon Hero to manage copious amounts of GIS data, the developers had to fixate on a different

type of footprint. A major development challenge was keeping Carbon Hero’s memory and storage consumption (its "footprint")

from exceeding a BlackBerry or Nokia device’s limited resources.

This is a common obstacle for mobile-mapping software. With on-device data storage of just a few megabytes and severely limited

RAM, programmers must wring the maximum efficiency from the smallest amount of code. This typically requires efficiencies

gained by developing applications in Java, C, C++ or other third-generation programming languages.

GIS data typically must be stored on a device, and managing such data efficiently is critical in minimizing the software’s burden on

scarce RAM, storage and CPU resources. Storing, sorting and retrieving data are the job of database management systems (DBMSs),

which aren’t as common in mobile applications as in enterprise and desktop software. Many developers in this environment still are

cobbling together "homegrown" databases, often in the form of flat operating system files.

But DBMS products (commercial, open-source and dual-licensed) designed specifically for integration within mobile devices

are becoming more common. One advantage is that these systems often include special data structures and other capabilities to

enable efficient management of mapping data.

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Figure 2. R-Tree searches can return rectangles that exactly match given coordinates, overlap given coordinates or

wholly contain given coordinates.

A critical tool for Carbon Hero turned out to be the R-Tree (sometimes called Guttman’s R-Tree, for its originator), a databasestructure designed specifically for efficient management of spatial data. Support for R-Trees is included in Perst Lite, an embedded

database system designed to operate in BlackBerry devices’ Java ME environment. Carbon Hero’s developers chose to embed Perst

Lite in their application.

What’s a Tree Index?In database system software, a tree index is a data structure that enables a query to "zero in" on specific records without searching

in linear fashion through entire database tables. The most common tree index, by far, is the B-Tree, which is efficient in "plain

vanilla" data queries such as exact match, prefix and range searches. But B-Tree indexes are single-dimensional and can’t deal with

the R2 or R3 coordinates required in spatial searches.

The R-Tree algorithm excels in this job by mapping objects in space using a "wrapping rectangle" or "bounding box." If an object

is represented by point coordinates (X, Y), then its bounding box is a degenerated rectangle in which the width and height are one.

For all other geographical objects (e.g., lines, polygons, other shapes, etc.), the bounding box is such that the coordinates of the

top-left corner are smaller than or equal to the coordinates of any point of the object, and the coordinates of the bottom-right corner are

greater than or equal to the coordinates of any point of the object. In other words, a wrapping rectangle is the smallest rectangle that

fully contains the specified object.

R-Tree indexes are commonly used to speed spatial searches (e.g., find the rectangle that bounds this point, find all rectangles that

overlap this rectangle, etc.). All manner of shapes can be stored and searched with the bounding box.

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Figure 3. The Carbon Hero application, which uses the R-Tree index, tracks an individual’s carbon-dioxide footprintthrough smarthphones or other mobile devices.

If a point is represented as a rectangle with width and height = 1, for example, a line that has starting and ending coordinates of 

(15, 844) and (0, 3647) is stored as a rectangle with its upper-left corner at (15, 844) and its lower-right corner at (0, 3647).

To determine if the two lines intersect or if a point is within a given area (described by a circle, rectangle, etc.), an R-Tree search is

performed to find all overlapping bounding boxes. For each match, a further test is conducted in the application code to determine

whether the condition is actually met.

In Figure 1, a search to discover all lines that intersect with (75, 15) (20, 70) would return the rectangle bounding (35, 25) (20, 30),

because the rectangles overlap. The application would extract additional information for the object (e.g., that it’s a line, its starting and

ending coordinates, etc.) and would conclude that this line doesn’t intersect and continue to the next overlapping rectangle returned by

the index search.

Note that any shape with coordinates {(X1, Y1), (X2, Y2), ... (Xn, Yn)} can be stored and searched in this manner. For example,

consider the polygon in Figure 2, where there are X coordinates of 35, 55, 65, 70, 85 as well as Y coordinates of 30, 33, 35, 45, 50,

63.

The bounding rectangle is the rectangle with left-top vertex (Xmax, Ymin), and right-bottom vertex (Xmin, Ymax) where Xmin =

min(Xi), Ymin = min(Yi), Xmax = max(Xi), Ymax = max(Yi). In this case, Xmax = 85, Ymin = 30, Xmin = 35, Ymax = 63 and the

rectangle top left and bottom right is (85, 30) and (35, 63).

R-Tree searches can return rectangles that exactly match given coordinates, overlap given coordinates or are wholly contained by

given coordinates.

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 Methods and Capabilities

The interface of a spatial index (R-Tree) typically provides the following search methods:

Locate objects belonging to a specified area (more formally, objects that overlap with the specified rectangle)

Locate objects that are part of the specified area (the objects for which the bounding box is wholly contained within the

specified rectangle)

Get all objects that belong to the specified area (all objects with bounding boxes that overlap with the specified rectangle)

According to Burch, the fast, efficient GIS indexing provided by R-Tree support "is just what we need for all of our mapping data."

For other functions, Carbon Hero relies on Perst Lite’s SortedCollections (implemented using T-Tree indexes) and TimeSeries classes

Burch singled out several database capabilities that help Carbon Hero operate within BlackBerry and other mobile devices’ limited

RAM, storage and CPU restrictions:

The database’s support for Java’s JSR 75 specification enables Carbon Hero to store records using a file system in flash

memory, an SD card or other media. This improves performance and storage-resource utilization markedly compared to using the Java

ME Record Management System persistent-storage mechanism.

As an object-oriented database, Perst Lite adds efficiency by storing data directly in Java objects, eliminating the translation

required for storage in relational and object-relational databases. This boosts run-time performance.

Burch praised the database system’s open-source, dual-licensing distribution for making development as easy as possible.

"We were able to get the source code straight away and start playing. If we wondered how something worked, we could look at the

source code," he adds. And because the database system has the backing of a "real" company, technical support was available.

Carbon Hero currently is in testing on BlackBerry devices in Europe. Zachariah and Burch have jointly filed for a patent on their

invention, and the idea has won a Sustainability Design Award from the British Standards Institute, among other honors.

The company foresees the application eventually running on a variety of GPS-enabled mobile devices. A key target market is

corporations, which will need to know the carbon footprint of their activities, including employee travel, to participate in

governments’ cap-and-trade carbon-emissions reduction programs as well as for corporate-reputation management, as consumers

increasingly base purchasing decisions on producers’ green credentials.