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| Consumer-grade
GPS for efficient GIS and mapping applications
R
M MIKOL |
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A
methodology for extending the geospatial
data collection functionality of the consumer-grade
GPS for circumstances that previously required
very expensive equipment, software and training |
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The GPS
is a ubiquitous tool on the planet today. Its
ability to pinpoint a person’s position
on the globe, and store information about that
location has been one of the most significant
contributions to society in the latter Twentieth
Century. Currently, the systematic collection
of geospatial attribute data is limited to very
expensive GPS receivers and specially trained
personnel. The general procedure for collecting
geospatial attributes with the consumer-grade
GPS has required the use of “add-ons”,
such as hand-held computers, laptops and palm
pilots. These add-ons are frequently outside of
the financial and technical reach of many communities,
organizations and under funded agencies. The protocols
and procedures presented here are designed to
modify and merge existing methods and technologies
to overcome these financial and technical barriers. |
| Methodology |
The GPS
provides four major data collection functions:
(1) precise location (waypoints);
(2) precise time (a date/time stamp at waypoint
collection);
(3) a name for that location; and
(4) tracks (routinely collected by the GPS, which
in turn can display an area surveyed).
While items: One (1), Two (2) and Four (4) are
self descriptive: item number Three (3) is the
data collection engine for this naming convention
protocol. It is in the waypoint name that the
user is able to record specific data attributes
about that location. For example, currently and
commonly the waypoint name provides a location
attribute such as “HOME,” for a persons’
domicile or an abbreviation like “ST_J_LK,”
for a place like St. John’s Lake. In the
GPS receiver’s small database, the waypoint
name is also the primary key field, in which no
two names can be alike. A common number of character
spaces provided on today’s GPS’ are
ten and the number of available alphanumeric characters
are 36 (10 numerals and 26 letters).
By using a data dictionary and a set of data structures
for the waypoint name, even casual GPS users can
provide organizations with high quality, accurate
and sophisticated geospatial data. This data,
created with the waypoint name, is both a unique
descriptor for that location and the primary key
value for the relational database. Also, once
the waypoint name is parsed, a set of data fields
are created with very specific attribute information
about the location surveyed. At a minimum, the
waypoint name and subsequent parsed fields should
describe: the GPS (including the operator); data
id and something about that location. In the event
of an oil spill, additional data might include
information on: shoreline type; presence of oil;
vegetation; birds; animals; mammals and fish.
An entire list of possible items need not be included
in the lists to describe the shoreline, vegetation,
etc. just those most common to the area. All of
the fields created in and parsed out from the
naming convention will be sorted out in the RDBMS.
Prior to any field use, a data dictionary should
be established. The nature of the survey will
determine the format and content of the naming
protocol and structure. For example a set of protocols
for mapping out a trail system might only have
five data entries in the name: GPS ID, Trail ID,
Data ID, and Trail Attribute ID. The number of
character spaces allotted for each data ID will
depend on the number of items involved in the
survey. If you do not expect to ever have more
than 36 GPS receivers in your database, then one
character space will be enough. The same is true
for the number of trails to be surveyed. On the
other hand, if the number of GPS units (or trails)
can be expected to exceed the amount of 36 over
the life of the project, then two character spaces
should be allocated. Two character spaces will
provide 1296 alphanumeric ID combinations. So,
a small trail mapping project might only have
one character space allocated for the GPS ID,
one space allocated for the Trail ID, two spaces
assigned to the Data ID and one space allocated
to the Trail Attribute ID. The waypoint name might
look like this: “270C4”. This waypoint
name, parsed out in the database provides the
following information: GPS #2 (owner, make and
model); Trail #7 (St. John’s Lake Trail,
23.8 km, moderate difficulty, average round trip
speed 6 ~ 8 hours); Data ID #0C (the 12th data
entry for that trail); Trail Attribute ID #4 (a
bridge). Connect this data into a GIS and you
have a trail made from tracks whose symbology
indicates moderate difficulty and a waypoint on
that trail that indicates a bridge. This same
set of protocols and database design can now be
modified for Search and Rescue (SAR): Trail ID
becomes Sector ID; and the Trail Attribute ID
becomes Hazard/Item of Interest Attribute ID.
Everything else stays the same.
Now imagine, 15 SAR personnel going out looking
for a lost hiker. Each has their GPS receiver
turned on, recording their tracks. Each member
of the team also has a waypoint naming convention
key that explains how to enter the waypoint name.
As each person returns to base, the data in the
GPS is downloaded directly into a database and
immediately displayed in the GIS for review and
analysis. At the end of the day a map document
is produced of their efforts, with minimal effort
and within a few minutes. |
| Coastal Oil
Spill Model |
Often
when an environmental disaster strikes, the nearest
local community is the first to know and the first
to respond. Federal and state government resources,
along with private contractors, though experts
in their field, often take days to fully mobilize.
During that time, precious information is lost
through the absence of data. This is an opportunity
where members of the community, with local knowledge
of plants, wildlife, and terrain, can be mobilized
to collect high quality, precision data with simple,
consumer-grade GPS receivers.
If a community is fortunate: then they have a
flexible response plan in place and have had an
opportunity practice that plan. The elements of
a response plan are likely to look like the following
outline:
• Purchase GPS units (or find out who has
them)
• Develop a data dictionary
• Develop a database (more precisely known
as a Relational Database Management
System or RDBMS)
• Figure 1, GPS waypoint naming convention
for the oil spill model
• Store the Data Dictionary in the RDBMS
(this can then be printed and distributed on a
moments notice)
• Simulate emergency situations and train
with the GPS receivers and GIS resources
In Figure 1, it is important to note that several
of the fields only allow for the specific choice
of 33 values, where three input values are reserve
characters for Not Present (0), Not Known (1)
and Other (Z). This is particularly useful when
a single character space is being used to identify
an attribute. In many cases, 33 variables will
be enough to identify the presence of a common
feature of concern |
| Data Collection |
Once and
emergency has been identified it will be important
to contact community members with knowledge of
all aspects of the local geography, including
the weather, vegetation and wildlife. Next, pass
out GPS receivers, the naming convention keys
and a map, along with a track line or area to
cover.
In the field, the waypoint data is collected according
to established protocols. This means that each
waypoint is given a name, and each character in
the waypoint name corresponds to a specific attribute
value in the data dictionary and that attribute
value is specific to the location in the waypoint
name. A written record is made of the data point
and this includes:
• Time of data entry
• Waypoint name
• Attributes identified
Additionally, tracks from the GPS are collected
according to protocol. Most likely this will simply
involve setting the “polling” rate
or the position data collection rate at a specific
interval. This may be a standardized rate of 10,
20, 30 or 60 seconds, or it may vary with each
GPS in order to distinguish
one GPS unit from another. |
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| November
2006 |
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