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Handehleds vs PNA?

 
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therock003
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PostPosted: Tue Apr 28, 2009 7:32 pm    Post subject: Handehleds vs PNA? Reply with quote

Hello guys, may i ask for someone to tell me how the handheld GPS units differ from the PNA's used in the cards?

I will be starting my job as a land surveyor and i'm consider the use of a GPS, but i wonder if the one i got for my car can get the job done as well.

So what are some of the basic differences?

Also how about maps?Do they support the same ones?
What kind of coordinate input do they support?
Are there any units better than the etrex?

These are some starter questions. I would really appreciate your help on the matter, as it would help me make my decision. Looking forward to your answer. Cool
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philpugh
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Location: Antrobus, Cheshire

PostPosted: Wed Apr 29, 2009 1:13 pm    Post subject: Reply with quote

Very wide question - but some basics to get you going.

PNA's for cars are designed with that in mind. The majority are not rain/water proof or even close to being rugged. Handhelds generally are designed with this in mind.

Also PNA devices are generally designed to "follow" roads - that is they take the actual position calculated by the GPS receiver and ensure that this is locked onto the nearest road. When you are off-road this can get in the way. Again some devices do allow 'off-road' work.

Position formats.

All road based PNDs use WGS84 reference - which is not usually a problem as very few people add information using Lat/Long (except people in this forum Laughing ) I know of one PND (my old GARMIN nuvi 660) that allows users to change to BNG (OS grid references and datum) but this is very much the exception rather than the rule.

All "handheld" GPS outdoor units will offer a range of map datums and position formats - more than any one person would expect to use in a lifetime.

Some of the modern handheld mapping units from GARMIN allow you to install their CityNavigator product which turns it into a full road navigation device - but the problem here is the screen is too small for safe use and the method of entering information can be fiddly - unless you go for the expensive touch-screen devices (Oregon series).

Mapping is a different matter. If you are wanting to use OSGB mapping then I would suggest that at present the best unit on the market is the SatMap Active10 which can have the whole of the UK at 1:50k or 1:25k - you can buy the areas you want by region / county / area. Other units (notably GARMIN) only have selected areas available in OS mapping. It is NOT possible to share mapping between different makes of devices and even between the same manufacturer you will probably have to pay an additional license fee to install a second copy of a map.

At the end of the day it will depend on what you actually want to achieve but I would suggest that, at present, it is probably better to have seperate units. Car navigation devices can be found at very reasonable prices - esp if you only want UK initially. I would stick to the main suppliers in this field (TomTom or GARMIN) and it's generally down to user preference as to which is best suited.

Best suggestion would be to go into a shop or two and have a look at the different units. Halfords have a decent range of car PNDs to look at and any good outdoor shop should have a range of handheld units to compare.
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therock003
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PostPosted: Wed Apr 29, 2009 6:28 pm    Post subject: Reply with quote

Since a handheld GPS is going to assist my professional needs, then i decided to go for the best. Please allow me to make some more specific questions about handheld units.

I'm either looking for the Oregon or the Colorado Series.

Are there any serious differences between them? I know that Oregon has a touchscreen but somehow it seems that people recommend the Colorado.

Are there any other handheld units known to be better or more complete than these two? Also any other manufacturer besides Garmin for handheld? I am only aware of magellan and the Triton series but i dont know if and how good they are.

Do they offer better accuracy as well? I know that PND can get as good as 5 meter accuracy. Is it possible to get 1-5 with an Oregon?
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mikealder
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Location: Blackpool , Lancs

PostPosted: Wed Apr 29, 2009 7:57 pm    Post subject: Reply with quote

As you are looking to use the device for survey work what is the accuracy you really need from the device? there are systems available that can offer very good positional accuracy but you won't get this sort of repeatable performance from a consumer navigation device.

The key to this is one of budget, the cost of high performance equipment is considerably higher than the basic kit you get with the Garmin/ TomTom products. What exactly are you intending to do with the hardware, mapping out farmers fields to an accuracy of a few feet is a little more demanding than driving up the M1, it also can take a few hours to set up - Mike
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therock003
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Joined: Feb 11, 2006
Posts: 14

PostPosted: Sat May 02, 2009 11:15 am    Post subject: Reply with quote

I will be using for surveying task of generic nature. For high accuracy i will be using a trimble r6 or r8 receiver.

So what do you have in mind? BTW what do you mean about taking a few hours to setup?
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philpugh
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PostPosted: Thu May 07, 2009 4:25 pm    Post subject: Reply with quote

The professional surveying GPS systems usually rely on DGPS (Differential GPS) services in order to get much greater and consistent accuracy (to within a few feet). Many of these use proprietary radio-based DGPS corrections - and it is this that takes the time to set up. There is a publicly "available" DGPS system (WAAS/EGNOS) that relies on corrections from geo-stationary satellites - but reception is 'iffy' especially in the northern regions of UK and it does require clear line-of-sight to a position just above the Southern horizon - so it's not very practical for many locations. Also, I believe, it offers lower precision than the commercial DGPS services - for which there is a charge.

If you have Internet connectivity you can also get DGPS corrections on-line - again there may be charges for this and I believe you can do this off-line - ie. log a series of postions (which will be date/time stamped) and apply the DGPS corrections later.

If you have a lot of time you can sample a static position for several hoyrs and average the result - this give very good accuracy - but it is reckoned that 24hrs sampling is required!

I've always fancied doing this on one of the OSGB Primary or Secondary trig sites - there is one 4 miles from me - their co-ordinates are very precisely known. Have a look at the OSGB site here

As you will see from this site the OSGB offer offline correction information from their RINEX system. NB you need to have professional GPS system and processing software to use this data - but you can achieve impressive accuracy (2cms) with as little as 30mins position averaging at your location.
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