GPS and trees

[Guest mcb]

It seems that a lot of people are bummed out when they go tromping off through the woods and their GPS only manages to get them to within a hundred or so feet of a cache and then sends them running around in circles. I think you're missing the fact that as you move through the woods you will be constantly be loosing and requiring lock on any give satellite. I don't care what kind of antenna you have you cannot receive a signal from a GPS satellite through a tree trunk and as you move through the woods you will inevitably block and unblock line of sight to many of these satellites. You won?t see this on the satellite page either. The satellite page only updates once a second or so and you won?t see most of the short looses of satellite signals. These interruptions can play havoc with the units ability to give you an accurate reading. It constantly has to calculate a position with data from different sources.

 

Stop every once in a while, hold you GPS up and let it get a good lock. Make sure you know what type of antenna you have (Patch/Quadrifilar) and what orientation is best for your give antenna. Move it around until you are talking to as many satellites as you think you can. The satellite screen is there to help to locate the satellites in the sky so that maybe you can move a little to find a hole in the canopy to get a better signal. Now just hold still and wait a while and give you GPS a minute to actually use data from all of these satellites to get a good fix on your location. Now take a bearing and a distance to the cache or waypoint you are navigation to and use your compass to head that direction for that distance. Figure out how long your pace is so you can estimate the distance you have traveled. Doing this you can even make a little yellow eTrex perform acceptably in the woods even though you may not maintain a continuous track.

 

Hope this helps

mcb

[Guest leemannn]

Hey thanks can you tell me what a

patch and quadrifilar antenna look like?

 

Lee

Provo ut

[Guest mcb]

It best to actually look in your manual or go to the manufacture's web site. I know with Garmin units The II, II+, III, III+ streetpilot GPS 76d and GPSMAP 76 have quadrifilar antennas. The eTrex/eMap series and 12 series have patch antennas. Both are good antennas althought the quadrifilar will have slighly better gains and is less sensitive to orientation.

 

If you have a patch antenna you want the base plan of the antenna horizonal. In an etrex or 12 this base plane is located under the Garmin logo at the top of the unit and should be held nearly parallel to the ground.

 

With quadrifilar antenna you want it stood up vertical. This is easily done with the external antenna on a II, III, or Streetpilot. On the GPS 76/GPSMAP 76 the quadrifilar antenna is internal and to get it vertical you need to hold the GPS nearly vertical for best reception.

 

I not to sure about the Magellan units but I am pretty sure the 315,320,330 unit have a quadrifilar type antenna and should be held up vertically. I don't own one so I am only assuming this.

 

mcb

[Guest brokenwing]

quote:

---

Originally posted by mcb:

I not to sure about the Magellan units but I am pretty sure the 315,320,330 unit have a quadrifilar type antenna and should be held up vertically. I don't own one so I am only assuming this.

---

 

Your assumptions are correct...

 

brokenwing

[Guest leemannn]

Thanks. Lee

[Guest Geoffrey]

I found a geocache yesterday with the Etrex Vista. For the first 45 minutes, it had me going in circles. I turned on the Electronic Compass feature, then went to the satellite page. Then moved the Vista around slowly until i got the best signal, then went to the Electronic compass, and took a bearing to the cache. Then found the cache quickly.

 

The best parts of the Etrex Vista is the Satellite page, and the Electronic compass. Go to within 150 feet of the cache, then switch to the satellite page. Hunt for a good satellite lock, then switch to the compass page quickly without moving the GPS. Take a bearing to the cache, then walk straight to where it said it was.

 

If you stare at the screen while walking toward the cache, it will throw you into another direction.

 

Doing this, i find that the Etrex Vista is better than the 3plus, because of the Vista's Electronic compass. My GPS 3plus had me going around in circles for an hour and a half, because i did not use the satellite page, and a GPS Bearing, and a sighting compass.

 

[This message has been edited by Geoffrey (edited 09 August 2001).]

[Guest gstrong1]

Geoffrey,please. Do this on a few more cache hunts & come back with results.As stated numerous times before I have the III Plus & the Vista & there is absolutely no way the Vista can touch the III Plus under tree cover.Again, maybe thats just the case up here in New York, but I doubt it .I could bring you to caches up here where I don't care if you climb a 20 ft. ladder with the Vista,your not going to get even 2D navigation.There is a cache in the Genesee County forest that is a 3/4 mile hike that will not give you a view of the sky once the whole hike.The Vista will not lock sats. 1 time.Of the 45 caches I've found, the Vista was rendered useless on at least 50% of them.With the III Plus,I don't go back & forth between screens & hold the unit up in the air on the satellite page to try to find where to point the unit to find a satellite.I hit goto, go to the compass page & follow the pointer to the cache.Under any conditions!

[Guest mcb]

The point of the thread, I guess, is that even with one of these "miserable eTrex" GPS units or an old multitrack 8 channel if you use your satellite page and a compass you can still find a cache. Look for openings in the tree canopy. Use natural features around you to get a good lock and then use you orientering skills to find the cache. If the cache is hidden in a place that makes GPS use difficult then locate a know point nearby and navigate there with your compass. I have done this on several caches and it works well. Geoffrey's method with his Vista was right on with what I was saying. I have done the same thing with a GPS and my regular handbearing compass. Same idea. If your GPS will take you to the cache directly then great. But one of these times whether it be heavey tree cover, multi path in a canyon, or bad satellite geometery you will eventually have a lock problem while cache hunting. Even with the mighty III+. I was just trying to say that you can compensate for poor conditions and still find the cache. The GPS is just a tool that has some limitation. The better you understand the limitation of a given tool the better you will be able to use the tool.

 

mcb

[Guest Jebediah]

rcPad software you can display your position atop an DOQQ or satellite imagery with other GIS files. With a cellphone modem you can correct right in the field for submeter accuracy. Cost for the entire setup is around $2000. Realtime correction will set you back ~$4500 up to ??.

 

Preplanning the trip will yield much better data too. At Trimble's website you can download their free Quickplan software which enables you to see PDOP and # of satellites up to 30 days in advance so you know when your unit is more accurate and when will accuracy drop. You can even factor in topography with a terrain mask for those days you are in canyon bottom. Print the screen and carry the graphs and tables with you.

 

I have found errors in a Garmin III+ of 102 meters with a PDOP of 2.5 and a SNR of 8. 5 satellite capture in an open field atop a survey control point. That was unusual. But since you generally cannot easily tell when you are very accurate or when the unit is displaying garbage I discount all of the recreational grade receivers. They are OK for finding your way back to a road but don't use them for serious mapping or field data collection.

For some unbiased field tests of various models go to:

http://www.fs.fed.us/database/gps/gpsusfs.htm "

[Guest Bob Bowter]

I too have a Vista and III+ and concur with most of gstrong1's observations.

 

On my resent hunt for the "Rattlesnake Hill Geocache", the Vista lost lock as I approached the cache. This was after a 4 miles of bushwhacking. As I continued towards the cache the III+ was hanging onto 3-6 birds and the Vista was unable to lock. Several attempts were made to get the Vista back into the game, but the gully and the trees cover above attenuated the signals beyond what the compact patch antenna in the Vista could work with. While filling out the logbook the satellite geometry improved and the Vista acquired.

 

My experience is that given good satellite geometry overhead, the Vista works under tree cover. This is the case much of the time. It's when birds needed for a position solution are sitting close to the horizon that it fails to remain locked.

 

I prefer to use the Vista whenever possible but when tree cover is dense and satellite geometry is poor, the III+ clearly the superior unit. Most of the 28 caches I have found have been with the Vista and I plan on using it as my primary GPSR. Like photos and hints, I only use the III+ if I can't find the cache after a reasonable amount of time. What's reasonable depends on how active the flies and mosquito's are that day.

[Guest gstrong1]

I'll take the jabs mcb & I am getting a little tired of rehashing this subject over & over again too so I will try to make this my last entry on this subject.There are a lot of experts here with the technological mumbo-jumbo to prove it. Said experts could probably find their way out of deep woods blinfolded.My real life experiences are aimed at the newbie looking to buy a unit & head out after some caches.I am in no way trying to convert anyone to any particular GPS.With the way this activity,sport or whatever you choose to call it is growing, there will be thousands of folks heading out after their 1st,2nd or 3rd caches under all kinds of conditions.Because of the nature of the beast, a lot of the caches will be in wooded areas.How many of those new cachers will go out totally prepared for whats out there? Will they all have heeded the advice administered in these forums regarding the need for a compass & the knowledge of its use?Will they allow themselves plenty of time in case they run into difficulty? Here's the scenario: Cacher gets out of work at 4:00 pm & has printed out the paperwork for a great cache he can stop for on the way home.Gets to the parking co-ordinates listed on the cache page & marks a waypoint there so he can get back to his starting point.Hits the goto for the cache waypoint & GPS says .780 mi. to the cache location so off he goes into the woods.After he's in a ways, he gets the old lost satellite signal message.Goes to the satellite page & starts holding the unit pointed in different directions to find where to get a lock, then moves on for another 150 ft. till he gets the message again.This happens 20 times between his car & the cache.Meanwhile, along his route he's gotten turned around 20 times because there's no real path to follow & he's run into obstacles he had to avoid.He's had to go up or down a few creeks to find a narrow spot so he can cross.He finally gets to the cache & he's elated with his success.Now it's time to head back out of the woods to his car.No problem because he knows he can use the track-back feature or just hit the goto for the wapoint he's stored for the car.He figures the track-back would be best because he knows that he has crossed the creeks at those locations & knows that he can cross there to get back. Thats when he realizes that he is totally dependant on the GPS to get him out of the woods & home for dinner.He looks at his watch & figures hes got a good 1/2 hour of daylight left & as soon as the first lost satellite signal message come up,panic sets in.He starts to go through the ritual of going to the satellte page & looking for lock but knows the clock is ticking & he's in real unfamiliar territory.He doesn't care about pdop,waas,snr values or any of that.He wants to get to his car before dark.The rest you can make up as you see fit. To you veterans, this is probably very long wided & old hat. But to you folks new to geocaching, know that this scenario has happened to someone for sure & will most assuredly happen again with the growth of the sport. Unfortunatly, we'll probably at some point hear about it here or on the local news.And I hope it's not you who's the cacher involved.I obviously don't care what GPS anyone purchases. I pass along my experiences with the III Plus only because I know it will get me home for dinner.I also have the MAP76 & the Vista & they are great units.I guess my point is, know the limitations of the unit you do have & prepare yourself for the worst. The odds are in your favor that the worst will not happen, but if it does, maybe you won't panic.Carry & know how to use a compass & pay attention to whatever you read on these posts.There's great info here from folks who have a lot of knowledge & experience. To you folks that are sick & tired of me rambling on about the III Plus, I'll do my best to stay away from the subject. I just love geocaching & am always thinking of the safety aspect of it.I'll shut up now. .

 

------------------

Gary "Gimpy" Strong

Rochester,NY

[Guest gstrong1]

I'll take the jabs mcb & I am getting a little tired of rehashing this subject over & over again too so I will try to make this my last entry on this subject.There are a lot of experts here with the technological mumbo-jumbo to prove it. Said experts could probably find their way out of deep woods blinfolded.My real life experiences are aimed at the newbie looking to buy a unit & head out after some caches.I am in no way trying to convert anyone to any particular GPS.With the way this activity,sport or whatever you choose to call it is growing, there will be thousands of folks heading out after their 1st,2nd or 3rd caches under all kinds of conditions.Because of the nature of the beast, a lot of the caches will be in wooded areas.How many of those new cachers will go out totally prepared for whats out there? Will they all have heeded the advice administered in these forums regarding the need for a compass & the knowledge of its use?Will they allow themselves plenty of time in case they run into difficulty? Here's the scenario: Cacher gets out of work at 4:00 pm & has printed out the paperwork for a great cache he can stop for on the way home.Gets to the parking co-ordinates listed on the cache page & marks a waypoint there so he can get back to his starting point.Hits the goto for the cache waypoint & GPS says .780 mi. to the cache location so off he goes into the woods.After he's in a ways, he gets the old lost satellite signal message.Goes to the satellite page & starts holding the unit pointed in different directions to find where to get a lock, then moves on for another 150 ft. till he gets the message again.This happens 20 times between his car & the cache.Meanwhile, along his route he's gotten turned around 20 times because there's no real path to follow & he's run into obstacles he had to avoid.He's had to go up or down a few creeks to find a narrow spot so he can cross.He finally gets to the cache & he's elated with his success.Now it's time to head back out of the woods to his car.No problem because he knows he can use the track-back feature or just hit the goto for the wapoint he's stored for the car.He figures the track-back would be best because he knows that he has crossed the creeks at those locations & knows that he can cross there to get back. Thats when he realizes that he is totally dependant on the GPS to get him out of the woods & home for dinner.He looks at his watch & figures hes got a good 1/2 hour of daylight left & as soon as the first lost satellite signal message come up,panic sets in.He starts to go through the ritual of going to the satellte page & looking for lock but knows the clock is ticking & he's in real unfamiliar territory.He doesn't care about pdop,waas,snr values or any of that.He wants to get to his car before dark.The rest you can make up as you see fit. To you veterans, this is probably very long wided & old hat. But to you folks new to geocaching, know that this scenario has happened to someone for sure & will most assuredly happen again with the growth of the sport. Unfortunatly, we'll probably at some point hear about it here or on the local news.And I hope it's not you who's the cacher involved.I obviously don't care what GPS anyone purchases. I pass along my experiences with the III Plus only because I know it will get me home for dinner.I also have the MAP76 & the Vista & they are great units.I guess my point is, know the limitations of the unit you do have & prepare yourself for the worst. The odds are in your favor that the worst will not happen, but if it does, maybe you won't panic.Carry & know how to use a compass & pay attention to whatever you read on these posts.There's great info here from folks who have a lot of knowledge & experience. To you folks that are sick & tired of me rambling on about the III Plus, I'll do my best to stay away from the subject. I just love geocaching & am always thinking of the safety aspect of it.I'll shut up now. .

 

------------------

Gary "Gimpy" Strong

Rochester,NY

[Guest mcb]

as nice as a III+ then there are other ways to get to the cache without maintaining a continuos lock. I understand you are fiercely loyal to your III+ and I can't blame you. I had one for a year and really loved it. Even though its starting to show it age with the features it has it still one of the most sensitive receiver going.

 

So if you are trying to decide what GPS unit to buy keep this discussion in mind. If you cut corners on price you may not get as sensitive unit as some of the more expensive models. Do research on the unit you are interested in and read more posts for users opinions on different units. If you already own a unit will a less then an optimal antenna then don?t worry there are way around that minor limitation. And don?t for get your compass just in case.

[Guest mcb]

as nice as a III+ then there are other ways to get to the cache without maintaining a continuos lock. I understand you are fiercely loyal to your III+ and I can't blame you. I had one for a year and really loved it. Even though its starting to show it age with the features it has it still one of the most sensitive receiver going.

 

So if you are trying to decide what GPS unit to buy keep this discussion in mind. If you cut corners on price you may not get as sensitive unit as some of the more expensive models. Do research on the unit you are interested in and read more posts for users opinions on different units. If you already own a unit will a less then an optimal antenna then don?t worry there are way around that minor limitation. And don?t for get your compass just in case.

[Guest Jebediah]

I think the point of the comment that I found and posted here was that ALL recreational-grade GPSRs are relatively inaccurate when it comes to location of precise points, even in the absence of cover, and the presence of it can make things worse by reducing the number of available birds. This has apparently been established in a number of objective field tests by the FS and others.

 

Some rec-grade receivers with effective antenna will continue to plot solutions, of course, but they may be inaccurate in terms of an actual position on the ground - and there is no warning that the data may be untrustworthy. This error could be up to 100 meters in some cases. I guess this means we can't automatically conclude we're getting accurate fixes even if we achieve sat lock.

 

Geocaching may well evolve as other activities, one side goes for sheer dedicated performance in one specific category - at the expense of practicality and versatility. I think searches for the ultimate in accurate receivers for one specific activity have their limitations. You can see this phenomenon in orienteering races where the compass even loses its degree markings - all is sacrificed to the god of terrain association. Dedicated orienteers tend to have a lot of trouble when the maps aren't large-scale and the land contours are insignificant.

 

As far as navigation goes, certainly we can make do with a lot less accuracy than that required for mapping or locating precise points. I know I can. I'm a firm believer in the simple, compact GPSR that is rugged and stays with you rather than the complex bulky model that stays home most of the time.

 

But if I understand your comment correctly, I would disagree that purchase of any one brand/model of GPSR can in any way compensate for lack of mapreading or compass skills, particularly when leaving paved roads or marked trails (especially a neophyte who plans a late afternoon search in heavy cover). Under such circumstances, relying solely on the performance of any model GPSR and its batteries because you don't have time to learn a potentially more time-consuming nav techique is foolish IMHO -even with the best receiver on the market, such conditions dictate a topo map, compass back bearing, knowledge of nearby linear features or handrails, and regular plotted positions as you move along your route.

 

We can also probably assume that the impatient geocacher described is packing very little in terms of survival/rescue/communication/overnight gear as well (where I usually go a cell phone is also useless). If the weather turns bad, this has the makings of not just a potential rescue, but a tragedy.

 

Even search and rescue teams who have let their map/compass skills go have gotten lost when their GPSR malfunctions. You simply cannot buy traditional map/compass reliability in an electronic battery-operated device, no matter what the model. I think we owe it to people to tell them that map/compass skills are not an afterthought we all cite as a mantra - there is NO satisfactory substitute for them if you choose to ignore their use.

 

 

[This message has been edited by Jebediah (edited 10 August 2001).]

[Guest k2dave]

Errors in the 100m range usually result from you receivig a bounced GPS signal. Since it bounced to you (off a cliff, building, etc.) The error will be much greater then the usual 'line of site' errors. Or such is how I understand it.

[Guest backcast]

Forgive me for reviving this thread, but after reading some of the posts, I felt compelled to add my 2 cents. I do not agree with some of the previous posts that claim the so called "recreational" GPS units are only accurate to a 100 feet or more.

 

As part of my job (geologist) I regularly use a GPS to locate geographical features as small as a mailbox for incorporation into GIS maps. I have used survey grade GPS systems with accuracies of better that 1 millimeter. However, I generally use a Garmin III+ to locate most features. It is easier to use and provides accurate enough data for most applications. Lets face it, we are not locating property lines in New York City.

 

To demonstrate the accuracy of the Garmin to others on my staff, we marked a waypoint at every 5th car in several rows in a large parking lot. We then downloaded a real world map of the waypoints with the freeware program "GPS Utility". Next, we imported the map into Autocad, overlaid it on a surveyed plan, and measured the distance in real space, between the waypoints. On average I found an accuracy of 10 to 20 feet. Some of the points were dead on, others off by more that 20 feet. You dont necessarily need a cad program to try this, basic GPS maping software will do.

 

We regularly download waypoints from the Garmin to the GIS and overlay them on aerial photos. Again, I have found the accuracy to be within 10 to 20 feet, its not uncommon for the III+ to be dead on. If any readings in the field are in doubt, we use the averaging feature on the III+ and take several waypoints around the location to be mapped. I have found several geocaches by just plotting the lat/long on the GIS aerial photos and taking a print out in the field with me.

[Guest CacheOut]

Appologies for adding another re-hash. I am a surveyor (under-ground/coal mining for the most part) and out of curiosity, took my Mag Meridian XL with a 1995 firmware date, with me yesterday to compare it with the mapping grade Trimble I sometimes use. Accuracy? 4sec lat and 6sec long between the Trimble and Magellan.

 

Tim

[Guest jfitzpat]

g this thread, but after reading some of the posts, I felt compelled to add my 2 cents. I do not agree with some of the previous posts that claim the so called "recreational" GPS units are only accurate to a 100 feet or more.

 

As part of my job (geologist) I regularly use a GPS to locate geographical features as small as a mailbox for incorporation into GIS maps. I have used survey grade GPS systems with accuracies of better that 1 millimeter. However, I generally use a Garmin III+ to locate most features. It is easier to use and provides accurate enough data for most applications. Lets face it, we are not locating property lines in New York City.

 

To demonstrate the accuracy of the Garmin to others on my staff, we marked a waypoint at every 5th car in several rows in a large parking lot. We then downloaded a real world map of the waypoints with the freeware program "GPS Utility". Next, we imported the map into Autocad, overlaid it on a surveyed plan, and measured the distance in real space, between the waypoints. On average I found an accuracy of 10 to 20 feet. Some of the points were dead on, others off by more that 20 feet. You dont necessarily need a cad program to try this, basic GPS maping software will do.

 

We regularly download waypoints from the Garmin to the GIS and overlay them on aerial photos. Again, I have found the accuracy to be within 10 to 20 feet, its not uncommon for the III+ to be dead on. If any readings in the field are in doubt, we use the averaging feature on the III+ and take several waypoints around the location to be mapped. I have found several geocaches by just plotting the lat/long on the GIS aerial photos and taking a print out in the field with me.

---

 

You can plot directly from your Garmin or Magellan right onto USGS NAPP images on our site http://www.lostoutdoors.com

 

I'd have to agree that average accuracy is 3-6 meters (about what the GPSr reports). I do have to laugh at the "refuse to incorporate..." comment quoted in an earlier post. A lot of GIS and GNIS coordinates are off by a fair amount when you plot them on NAPP or sat. images.

 

-jjf

[Guest Kerry]

What some users tend to miss with some of the experiments is that yeah most of the time it's reasonbaly close but the miss-conception is that the accuracy will be always that close, not so. There's more to it than just flashing a GPS up (any GPS) pushing the button that says store and have a value that fits cosy experiments, which can sometimes give users the totally wrong impression.

 

That store and believe button can be one over confident miss-leading button.

 

Just a curious question does/did the Meridan XL have the fabled Magellan auto-averaging?

 

Cheers, Kerry.

[Guest bradrobb]

Most of my finds have been urban caches and I have not had trouble yet. But I do use my GPS to go out on hikes and I have a Topo map software program for Ontario. When I go hiking I print the map for the area and plot my intented target for the hike and the use the UTM location and enter it in my GPS and use it as a guide. I still use the old map and compass. I wish we had GPS's when I was in the military in the 80's. I agree with most postings, to do serious outdoor activities you should by able to use a map and compass first and not let the GPS be the your only nav tool. And carry a cellphone to call if you need help.

[Guest Rich in NEPA]

quote:

---

Originally posted by mcb:

On the GPS 76/GPSMAP 76 the quadrifilar antenna is internal and to get it vertical you need to hold the GPS nearly vertical for best reception.

---

 

Does anyone know for a fact which way the QF antenna is oriented in the GPS76 and GPSmap76? I mean, if it's located at the top end of the unit, it *could* be mounted horizontally. The shape of the case at that end seems to indicate it, as well as the proximity of the battery compartment.

 

So, my question is: if the antenna is oriented in a horizontal position, is it still best to keep the unit vertical?

 

------------------

~Rich in NEPA~

 

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? A man with a GPS receiver knows where he is; a man with two GPS receivers is never sure. ?

====================================================================

[Guest backcast]

Thanks for the website jfitzpat. That will come in handy when I am not at work.

[Guest Kerry]

quote:

---

Originally posted by CacheOut:

Appologies for adding another re-hash. I am a surveyor (under-ground/coal mining for the most part) and out of curiosity, took my Mag Meridian XL with a 1995 firmware date, with me yesterday to compare it with the mapping grade Trimble I sometimes use. Accuracy? 4sec lat and 6sec long between the Trimble and Magellan.

Tim

---

 

Tim, so what do you expect the problem is? there's something rather funny with that difference.

 

Cheers, Kerry.

[Guest jfitzpat]

quote:

---

Originally posted by Kerry:

Tim, so what do you expect the problem is? there's something rather funny with that difference.

 

Cheers, Kerry.

 

---

 

Sounding pretty big to me too... Different Datum?

 

-jjf

[Guest Geoffrey]

tinuous circles about 100 feet in diameter. I visited the cache area 5 times now, in the summer, fall, and winter, and got the same results each time. I tell you, it's those darn trees. I have had a few caches that made my 3+ and 5 nearly useless, but had friends with sharp eyes find the caches for me. They seemed to do better if they had no GPS in their hand, and concentrated on looking for the cache container.

 

I would like Garmin to put averaging into the vista, so you could average your position while pointing your vista's compass at a cache, then after a couple minutes, it could give you a reliable reading.

 

Things to contend with:

1) Trees (Big fat signal blockers)

2) Any object that reflects an errored signal back at your GPS.

3) Accuracy of the coordinates that the cache placer put on the cache page.

4) And then how well the cache was concealed.

 

------------------

Geoff's GPS Information Page

 

Geoff's Information on GPS units, and price guide for several units

 

[This message has been edited by Geoffrey (edited 17 February 2002).]

[Guest Geoffrey]

Out of all my GPS units ive had, including Magellan and Garmins, the best one is the GPS V, for hiking, Jogging and Running. It seems to give me a very accurate track log, even when i run past some trees. Tracklog wise, my GPS 315, GPS 3,and vista doesnt compare with the GPS V.