GPS Receivers for GIS Data Collection

GPS Receivers for GIS Data Collection
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Survey & Construction Newsletter, Mid-June 2009

Jun 22, 2009
By: Eric Gakstatter
GPS World

In my last issue, I proclaimed the start of GPS/GIS month, with a focus o=
n the subject in=20
three of my newsletters. This is the second in that series. The first col=
umn can be read=20
here. Also, I=E2=80=99m hosting a webinar June 30 to discuss using GPS re=
ceivers and technology=20
for GIS data collection. In my last newsletter I discussed the use of con=
sumer GPS=20
receivers for GIS data collection. Remember the analogy I used=E2=80=A6a =
Volkswagen Beetle wasn=E2=80=99t=20
designed to run in a Formula One race? This column is going to focus on t=
he Formula One=20
cars, not the Volkswagen Beetles. In other words, it will focus on the GP=
S receivers on=20
the market that are designed for GIS data collection. I will refer to the=
m as GPS/GIS=20
receivers.

What differentiates a GPS/GIS receiver from any other GPS receiver?

The number-one differentiator is that GPS/GIS receivers are designed do a=
better job of=20
optimizing tracking and accuracy in areas where GIS data collection is pe=
rformed. The=20
operative term is =E2=80=9Care designed.=E2=80=9D Specifically, engineers=
who designed GPS/GIS receivers=20
do so with different design criteria than engineers who design consumer G=
PS receivers and=20
even survey GPS receivers. For example, a GPS/GIS receiver must be design=
ed to operate=20
where GIS data is collected and with reasonable accuracy. On the other ha=
nd, consumer GPS=20
receivers are designed to track in tough conditions, but at the expense o=
f accuracy.=20
Furthermore, survey GPS receivers hold accuracy as the number-one priorit=
y so they=20
sacrifice the ability to track in many environments.

The following matrix illustrates my point
(1 =3D Highest priority design consideration, 5 =3D Lowest priority desig=
n consideration):

Consumer GPS GPS/GIS receivers Survey receivers
-----------------------------------------------------------------------
Accuracy 4 2 1
Tracking 1 3 5
Data collection 5 1 2



There are thousands of designers of consumer GPS receivers (Garmin, TomTo=
m, Magellan,=20
etc.) and probably only 10 designers of GPS receivers for surveying (Trim=
ble,=20
Leica/NovAtel, Topcon, Magellan, Septentrio, JAVAD GNSS, NavCom, etc.). T=
here are even=20
fewer designers of GPS/GIS receivers =E2=80=94 less than 10 (Trimble, Mag=
ellan, Topcon, Geneq,=20
Sokkia, Hemisphere, JAVAD GNSS, ViaSat).

o The market for GPS/GIS receivers is a complicated one. That=E2=80=99s t=
he primary reason why=20
there are only a few manufacturers. Here are some of the reasons why it i=
s complex:

o Users require a GPS receiver that will work effectively in many differe=
nt and=20
challenging environments such as under trees, in mountainous areas and ne=
ar buildings.=20
There is not one product on the market that will meet every user=E2=80=99=
s requirements.

o Users have various needs for the type of GIS data collected. For exampl=
e, some only need=20
two or three attributes for a utility pole and others may need to collect=
dynamic line=20
segments such as speed zones and road lane types.

There is not an effective way for manufacturers to distribute such produc=
ts. The=20
traditional survey instrument dealers (not all) are not typically trained=
or experienced=20
in GPS/GIS technology. Since there is not an effective distribution chann=
el, the=20
alternative is to create a grass-roots distribution channel, which is ver=
y time-consuming.
There are many factors to consider when attempting to determine what sort=
of GPS/GIS data=20
collection system best fits a user=E2=80=99s requirements. Here are some =
in order of priority:

1. Budget. One could argue that data collection requirements should be #1=
=2E Maybe, but that=20
depends on what stage of planning you=E2=80=99re in. If you are in the bu=
dget planning phase and=20
are able to influence it, then I agree that user requirements should be t=
he first=20
priority. However, the vast majority of people I encounter are given an e=
stablished budget=20
to work within. In that case, budget should be #1 because it=E2=80=99s a =
waste of time to consider=20
solutions outside of the budget constraint.

2. Accuracy. When I ask a potential GPS/GIS user what their accuracy requ=
irement is, the=20
typical answer is =E2=80=9Cas accurate as I can get=E2=80=9D. Of course, =
you can imagine the ensuing=20
conversation=E2=80=A6

Me: Well, Ok, you can achieve results around a centimeter.
Them: That=E2=80=99s great. A centimeter is perfect.
Me: Ok, here are the cost and training requirements.
Them: Wow, why is it so expensive???????
Me: There is a direct relationship between accuracy and cost. The more ac=
curate you want,=20
the more expensive it=E2=80=99s going to be.
Them: Well, Ok, we reeeeally only need to be within about three feet.
Me: Do you need elevation values within three feet?
Them (now leery of the response to their answers): Will those cost more?
Me: Yes, probably quite a bit more.
Them: No, we don=E2=80=99t need elevations.

3. Data collection requirements. Essentially, consumer GPS receivers and =
survey GPS=20
systems =E2=80=9Cthink=E2=80=9D in terms of points. More specifically, co=
nsumer GPS receivers operate in=20
terms of waypoints and survey GPS systems operate in terms of point avera=
ging.
Some of the more sophisticated survey GPS systems offer Field-to-Finish (=
F2F) capability=20
whereas points are automatically connected to form a line back in the off=
ice such as with=20
curbs and property lines.

GIS data collection systems are different. GIS =E2=80=9Csees=E2=80=9D the=
world in one of three ways;=20
points, lines (or polylines) and areas (or polygons). All have some level=
of database=20
information attached. For example, a fire hydrant is a point on a map but=
there is also=20
information in the GIS about that fire hydrant such as condition, last in=
spection date,=20
etc. A parcel is a polygon on a map but there is also information in the =
GIS about that=20
parcel such as ownership, tax id, etc.
Additionally, there are several methods to record all three.

For example, a wetland biologist may be mapping the perimeter of a wetlan=
d area but wants=20
to =E2=80=9Ctake points=E2=80=9D on certain habitat nests he/she sees whi=
le walking the perimeter. Some of=20
the more powerful GIS data collection software is built so the biologist =
can temporarily=20
suspend mapping the perimeter and be allowed to map the next site and res=
ume mapping the=20
perimeter when point recording is finished.

Using the proper data collection software that matches the user requireme=
nts can save a=20
significant amount of time and energy.


4. Data collection conditions. This is the biggest =E2=80=9Cgotcha=E2=80=9D=
for GPS/GIS receivers. A=20
certain GPS receiver designed for GIS data collection may perform flawles=
sly in the=20
open-sky and works perfectly well for uses such as agriculture or other o=
pen-sky=20
environments. However, most uses consist of some or all work done in =E2=80=
=9Cless-than-ideal=E2=80=9D GPS=20
conditions. Tree canopy is the biggest culprit. In that scenario, receive=
r performance can=20
differ significantly. Some won=E2=80=99t track at all in those environmen=
ts and some will track=20
very well, but accept excessively noisy satellite measurements (which sig=
nificantly=20
degrades accuracy). The best ones are designed with a keen balance of sat=
ellite tracking=20
and accuracy =E2=80=93 with settings the user can change depending on the=
environment.
Why are GPS/GIS receivers so much more expensive than consumer GPS receiv=
ers?

Part of the reason that consumer GPS receivers are adapted to GPS/GIS dat=
a collection is=20
the significant difference in cost. A consumer GPS receiver can be purcha=
sed for well=20
under US$200. The entry level price for a GPS receiver with comparable ac=
curacy, but with=20
GIS data collection features is four times that. Furthermore, the entry l=
evel price for a=20
GPS/GIS receiver capable of sub-meter accuracy is about $2,000.

There are several specific and justifiable reasons for the price differen=
ce, but suffice=20
to say that significantly more design engineering, technical support and =
sales effort is=20
involved with GPS/GIS receivers. Furthermore, the volume of GPS/GIS recei=
vers is miniscule=20
compared to consumer receivers. If there were tens of millions of GPS/GIS=
receivers=20
manufactured and sold every year, the price would be under US$200 each. B=
ut the GIS market=20
just isn=E2=80=99t that large. Therefore, GPS/GIS manufacturers have to c=
harge more per unit to=20
account for engineering, technical support and sales overhead.

Lastly, as mentioned above, there are not very many manufacturers of GPS/=
GIS receivers.=20
Lack of competition usually results in higher prices to the end user.

What sources of GPS corrections are available?
Autonomous (no differential correction applied) GPS is pretty accurate th=
ese days=E2=80=A6on the=20
order of a few meters. For this reason, consumer GPS receiver manufacture=
rs tend to leave=20
out information on GPS corrections in their specifications. Their rationa=
le is that=20
consumers don=E2=80=99t really care as long as they can navigate effectiv=
ely.

However, the GPS/GIS receiver market is much more concerned with accuracy=
=2E Therefore, some=20
sort of GPS correction source is highly recommended and necessary to achi=
eve the desired=20
accuracy.

There are essentially two types of GPS corrections: real-time and post-pr=
ocessing.

Throughout the 1980s and 1990s, post-processing was the dominant method o=
f correcting GPS=20
data. Even then, 2-5 meter accuracy was the norm for GPS/GIS receivers af=
ter=20
post-processing was applied. Sub-meter GPS technology (using GPS/GIS rece=
ivers) only=20
became possible towards the end of the 1990=E2=80=99s. Users were accusto=
med to going through the=20
post-processing exercise (downloading base station data, QAing post-proce=
ssed data, etc.).=20
At that time, the only option for using real-time corrections were commer=
cial services=20
such as OmniSTAR.

In the mid-1990s, the U.S. Coast Guard (USCG) established the DGPS system=
that broadcast=20
real-time GPS corrections free of charge along the US coastlines and majo=
r waterways. The=20
user only needed to purchase equipment (beacon receiver) to receive the s=
ignal. The=20
success of that program lead to the U.S. Department of Transportation (DO=
T) to expand the=20
program to cover inland regions that were out of the USCG domain. That wa=
s the GPS/GIS=20
user=E2=80=99s first taste of free DGPS corrections=E2=80=A6and they like=
d it because it eliminated the=20
time-consuming (and sometimes painful) process of post-processing.

The break-out milestone for real-time corrections came in 2003 when the F=
ederal Aviation=20
Administration (FAA) declared the Wide Area Augmentation System (WAAS) op=
erational. WAAS=20
took real-time GPS corrections to another level of simplicity. Not only i=
s WAAS free of=20
charge to users, but unlike the USCG DGPS and commercial DGPS services, i=
t=E2=80=99s broadcast on=20
the same frequency as GPS. This means that no extra antenna or receiver i=
s required to=20
utilize the signal. Furthermore, it=E2=80=99s broadcast nation-wide in th=
e US where ever the WAAS=20
satellites are visible to the user. Due to the success of WAAS, several o=
ther regions in=20
the world have deployed similar systems; EGNOS in Western Europe, MSAS in=
Japan/Korea and=20
GAGAN in India.

Finally, in the early part of this decade, local networks of reference st=
ations began=20
springing up. These are called RTK Networks. While built primarily for us=
ers of survey GPS=20
receivers who require cm-level accuracy, there is a growing population of=
GPS/GIS users=20
who are connecting their GPS/GIS receivers to these networks to obtain GP=
S corrections.=20
However, the costs can be expensive. Some network operators charge a fee =
to access their=20
network and the user must also have a data subscription with a wireless p=
rovider (GSM or=20
CDMA) which has a monthly fee associated with it =E2=80=94 similar to a m=
obile phone.

The Future is Clear
The trend is clearly towards using real-time GPS corrections no matter wh=
ich source is=20
used. The time consumed by post-processing and the expense of maintaining=
software and=20
training requirements adds too much overhead in most applications for org=
anizations to=20
consider it.Although not the dominate correction technology any longer, p=
ost-processing in=20
the GPS/GIS segment still has a niche =E2=80=93 the so-called =E2=80=9Csu=
b-foot=E2=80=9D niche. While the majority=20
of GIS applications are satisfied with =E2=80=9Csub-meter=E2=80=9D (or ev=
en 1-3 meter) accuracy, there are=20
certain applications where =E2=80=9Csub-foot=E2=80=9D accuracy is require=
d. With these receivers, the=20
users must post-process against several reference stations or tie into an=
RTK Network.

Integrated =E2=80=9CAll-in-one=E2=80=9D GPS/GIS receiver or separate stan=
d-alone receiver?
In the GPS/GIS receiver market, there are clearly two types of systems. T=
he =E2=80=9CAll-in-one=E2=80=9D=20
receivers have the GPS receiver, antenna and data collector built into a =
hand-held format.=20
These are products such as the Trimble GeoXT/XH, Magellan Mobile Mapper C=
X/6 and Topcon GMS-2.

The =E2=80=9Cstand-alone=E2=80=9D receivers are a =E2=80=9Cblack box=E2=80=
=9D which houses only the GPS receiver, GPS=20
antenna and optionally a battery. Other devices such as PDAs, tablet comp=
uters and=20
notebook computers receive GPS data from these stand-alone receivers typi=
cally via=20
Bluetooth interface or cable connection. These are products such as the T=
rimble ProXT/XH,=20
Geneq SX Blue, Sokkia GIR1600, Hemisphere A100 and Javad GISMore.

There are advantages and disadvantages to both.

=E2=80=9CAll-in-one=E2=80=9D receivers house everything one needs in a si=
ngle hand-held unit. The=20
advantage is that the data collector, GPS receiver, antenna, battery syst=
em, etc. are all=20
designed by one company to work together. On the other hand, designing al=
l of these=20
components into a single hand-held can make for a somewhat heavier unit. =
Also, PDA=20
technology is evolving rapidly. =E2=80=9CAll-in-one=E2=80=9D receivers ar=
en=E2=80=99t updated nearly as fast as=20
PDA technology so an =E2=80=9CAll-in-one=E2=80=9D unit may have an out-da=
ted operating system and/or=20
processor if the design is a few years old.

=E2=80=9CStand-alone=E2=80=9D receivers are separate receivers that send =
GPS data to a PDA, tablet=20
computer or notebook computer via wireless Bluetooth or cable connection.=
The advantage of=20
these systems is flexibility. On one project, they can be interfaced to a=
PDA. On the next=20
project, they can be interfaced to a notebook computer running different =
mapping software.=20
They aren=E2=80=99t affected by the advancement of PDA, operating system =
or computer processor=20
technology.

The Final Analysis =E2=80=94 GPS/GIS receivers for GIS data collection.
There a myriad of GPS receiver technologies being used for GIS data colle=
ction. It=E2=80=99s a=20
complex industry. Some receivers being used are purpose-built and others =
have been adapted=20
from other industries like consumer GPS.

There is no magic formula to determine which GPS receiver will work best =
because it really=20
depends on the user=E2=80=99s requirements and in GIS, the user requireme=
nt vary greatly. =E2=80=9CTry=20
before you buy=E2=80=9D is the best advice to follow when going through t=
he equipment/software=20
selection process.

If you have time, I=E2=80=99m conducting a GPS/GIS receiver webinar on Ju=
ne 30 (next Tuesday) at=20
10:00 a.m. Pacific time. I will continue the discussion of GPS/GIS receiv=
er selection.=20
Register for the webinar here.

http://sc.gpsworld.com/gpssc/content/printContentPopup.jsp?id=3D605574=

[note - this article is better read from the above URL.]