Best Handheld in forested area?

Per David Wetmore:
level of the 60CSx. The Oregon interface is

Has anybody tried the Oregon touch-screen interface while the
unit is in a waterproof bag?
--
PeteCresswell

polecanoe wrote:

GPS Receivers for GIS Data Collection
http://sc.gpsworld.com/gpssc/content/printContentPopup.jsp?id=3D605574=

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

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=92m hosting a webinar June 30 to discuss using GPS receiver=
s 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=85a Volksw=
agen Beetle wasn=92t=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 =93are designed.=94 Specifically, engineers who designe=
d 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 =97 less than 10 (Trimble, Magellan,=
Topcon, Geneq,=20
Sokkia, Hemisphere, JAVAD GNSS, ViaSat).

o The market for GPS/GIS receivers is a complicated one. That=92s the pri=
mary 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=92s requ=
irements.

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=92s requirements. Here are some in ord=
er 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=92re in. If you are in the budget p=
lanning 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=92s 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 =93as accurate as I can get=94. Of course, you can imag=
ine the ensuing=20
conversation=85

Me: Well, Ok, you can achieve results around a centimeter.
Them: That=92s 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=92s 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=92t need elevations.

3. Data collection requirements. Essentially, consumer GPS receivers and =
survey GPS=20
systems =93think=94 in terms of points. More specifically, consumer GPS r=
eceivers 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 =93sees=94 the world in on=
e 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 =93take points=94 on certain habitat nests he/she sees while walking t=
he 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 =93gotcha=94 for GPS/G=
IS 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 =93l=
ess-than-ideal=94 GPS=20
conditions. Tree canopy is the biggest culprit. In that scenario, receive=
r performance can=20
differ significantly. Some won=92t track at all in those environments 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 =96 with settings the user can change depending on the envir=
onment.
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=92t that large. Therefore, GPS/GIS manufacturers have to charge =
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=85on 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=92t really care as long as they can navigate effectively.

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=92s. Users were accustomed 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=92s first taste of free DGPS corrections=85and they liked 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=92s 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=92s broadcast nation-wide in the US w=
here 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 =97 similar to a mobile =
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 =96 the so-called =93sub-foot=94 ni=
che. While the majority=20
of GIS applications are satisfied with =93sub-meter=94 (or even 1-3 meter=
) accuracy, there are=20
certain applications where =93sub-foot=94 accuracy is required. With thes=
e receivers, the=20
users must post-process against several reference stations or tie into an=
RTK Network.

Integrated =93All-in-one=94 GPS/GIS receiver or separate stand-alone rece=
iver?
In the GPS/GIS receiver market, there are clearly two types of systems. T=
he =93All-in-one=94=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 =93stand-alone=94 receivers are a =93black box=94 which houses only t=
he 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.

=93All-in-one=94 receivers house everything one needs in a single hand-he=
ld 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. =93All-in-one=94 receivers aren=92t updat=
ed nearly as fast as=20
PDA technology so an =93All-in-one=94 unit may have an out-dated operatin=
g system and/or=20
processor if the design is a few years old.

=93Stand-alone=94 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=92t affected by the advancement of PDA, operating system or com=
puter processor=20
technology.

The Final Analysis =97 GPS/GIS receivers for GIS data collection.
There a myriad of GPS receiver technologies being used for GIS data colle=
ction. It=92s 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=92s requirements and in GIS, the user requirement var=
y greatly. =93Try=20
before you buy=94 is the best advice to follow when going through the equ=
ipment/software=20
selection process.

If you have time, I=92m conducting a GPS/GIS receiver webinar on June 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.]

Use this URL: http://www.gpsworld.com/survey/gps-receivers-gis-data-colle=
ction-7312

Sam Wormley wrote:

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4

To answer your question directly, I would go with the Vista HCx. I have one
and am very impressed with its sensitivity. It picks up satellite signals
well in two story houses, in the middle of vehicles, and aircraft (window
seats). And top notch accuracy.

EW

polecanoe wrote:

The better Garmin receivers are the 60/76 Cx/CSx models. They have the
SiRF III chip set and Quadrifilar Helix antennas. The eTrex Vista HCx
has a patch antenna and will not perform as well as the ones with the
Quadrifilar Helix antennas.

The HCx has Garmin's "high performance" GPS chip set it in. That is a
clone of the SiRF III chip set. It had some issues when first released,
those have been resolved I think. It might be as good as the SiRF III
but it is no better.

I also responded to your post on the Garmin group, I won't repeat that here.

Jack