Projecting waypoints in the field

[+Zartimus]

Hello all. One thing that I don't like is that some GPS units (at least the two I have owned) only seem to let you project waypoints in large units like kilometers/miles with only 0.2 decimal places of precision. If I want to project a waypoint 475 meters in a particular direction, I am forced to enter it as 0.47 kilometers, so right out of the blocks I am off by 5 meters, not counting the 3-6 meter accuracy of the GPSr itself.

 

I have an Etrex Legend and have been through the manual. Anyone know of a way to allow waypoint projection to be entered in meters? I think I'll email the good folks at Garmin.

 

So lately I'm forced to go out, take co-ords, and come back home to use software to be accurate. If I had just one more decimal place of accuracy, life would be great!

 

[This message was edited by Zartimus(carrdav) on May 04, 2002 at 06:58 PM.]

[+apersson850]

projecting a waypoint inherently means from somewhere. If we assume that you are standing at a position, determined by the GPS, there is hardly any reason to project a distance with better resolution than 10 meters, since a resolution of one meter would be blurred by the accuracy of the GPS. According to my experience, an accuracy of 5-10 meters is quite common.

 

Data you store, information you use.

 

[This message was edited by Anders on May 06, 2002 at 11:17 PM.]

[+Renegade Knight]

A reason is accuracy. Your GPS is only so accurate, but when projecting a waypoint why make it even more inaccurate just because the GPS sofware forces you to? A 475 meter line is 475 meters long. Not 470 or 480.

 

A good example in geocaching standing on a starting point and projecting a waypoint along a certain bearing and for a certain distance to find the cache. I have set up one cache like this.

 

Your GPS is smart enough to project down to the nearest foot if only the sofware would let you.

[OFF RODE]

My G3+ allows entrys to the foot, but as stated thats way mor accurate then the GPSr can determine, but it does make me feel a bit more precise.

 

"You've got to be very careful if you don't know where you're going, because you might not get there." Yogi Berra

JeepNAz@aol.com

[+Olar]

Don't feel bad. My GPS V is only calibrated down to .1 KM (100 metres). Not very useful although I've never had a reason to use it. Just the same for the cost of these units you would think at least 2 decimal places would be expected.

Olar

 

[+Alan2]

quote:

---

Originally posted by Zartimus(carrdav):... If I want to project a waypoint 475 meters in a particular direction, ...

---

 

Why would you want to do this? Can you give us a real world example?

 

Alan

[+Zartimus]

The whole reason I had to do this was the "Hidden Treasure" geocache by Binthair, Quite neat actually and I will not give away the trick in this post. It is 4 inches in diameter so it pays to be right on top of it in the end.

 

Here is the dilemma.

 

Take this waypoint, "TR1"

TR1 N45°26.0660' W075°34.5950'

 

If I use software and start here and take a bearing of 332.2 degrees (magnetic) and travel a distance of 195 meters, I arrive at the following waypoint(TR2).

 

TR2 N45°26.1590' W075°34.6650'

 

This was done with software.

 

If I perform this in the field with the Etrex Legend, and it's 10 meter limitation when it comes to projecting waypoints, I am forced to enter 0.19 kilometers instead of 195 kilometers. This is where I have the problem. It takes me here: N45°26.1567' W075°34.6631' that is quite a bit off and it would not be if only there was an extra level of precision. If I could enter 0.195 kilometers, I'd be very happy.

 

It seems to me to be a simple enough thing to fix since it is math and has nothing to do with sat acquisition. It could probably be done with a firmware upgrade.

 

Garmin inquiries have directed me to survey GPS's but I think they are mis-understanding my question. This stuff can be performed in the "GPS Off" mode.

[+Alan2]

quote:

---

Originally posted by Zartimus(carrdav):

...

Here is the dilemma.

 

Take this waypoint, "TR1"

TR1 N45°26.0660' W075°34.5950'

 

If I use software and start here and take a bearing of 332.2 degrees (magnetic) and travel a distance of 195 meters, I arrive at the following waypoint(TR2).

 

TR2 N45°26.1590' W075°34.6650'

 

This was done with software.

 

If I perform this in the field with the Etrex Legend, ....

---

 

I still must be missing something. Why would you need to project something like that. The GPS in the field projects a waypoint that's a guess. What other reason would youn have to project/ I mean how would you know exactly 475 meters? If you calculated that at home on a computer, why would you need a Legend to do it for you?

 

Alan

[+Alan2]

quote:

---

Originally posted by Zartimus(carrdav):

...

Here is the dilemma.

 

Take this waypoint, "TR1"

TR1 N45°26.0660' W075°34.5950'

 

If I use software and start here and take a bearing of 332.2 degrees (magnetic) and travel a distance of 195 meters, I arrive at the following waypoint(TR2).

 

TR2 N45°26.1590' W075°34.6650'

 

This was done with software.

 

If I perform this in the field with the Etrex Legend, ....

---

 

I still must be missing something. Why would you need to project something like that. The GPS in the field projects a waypoint that's a guess. What other reason would youn have to project/ I mean how would you know exactly 475 meters? If you calculated that at home on a computer, why would you need a Legend to do it for you?

 

Alan

[+Navdog]

We placed the mult-leg cache Rimwalker II recently, which requires using waypoint projections and compass bearings. Cachers haven't had any problems finding the tags on the projection legs, except for one, who just wasn't able to spot one, although he was right on top of it. We were sure to use legs that were .10 and .20 miles in length to be sure most GPSR's would work.

 

Although, we experimented with just walking a bearing line and distance from the initial waypoint and found this allowed us to zero in on the next tag just as effectively. It just requires a little more attention to where you are walking.

 

My GPSV only allows a .10 mi. minimum projection, but my Vista allows .01 as the minimum. Wish they would have changed that on the 2.03 firmware update.

 

"I may not have gone where I intended to go, but I think I have ended up where I intended to be."

-Douglas Adams

[+Alan2]

Navdog, I could see from your pix that being off on your projection of a waypoint could make for a bad day geocaching being that close to the canyon rim.

 

I think now I understand what you guys are doing. You give the coordinates to intermediate waypoint "A" to everyone. You then plant the cache at "B" and either walk the distance off from "A" or I suppose measure the distance using your computer and then give that distance as a projected waypoint.

 

Other than for offset geocaching, it doesn't seem to serve any other purpose. I mean if you either walked to the new spot which you would have done if you hid a cache or you used a computer to "see" the new spot. Either way you would know the "projected" coordinates and would give the actual coordinates to anyone who was not playing geocaching. Not much reason for manufacturers to be that accurate to the meter since no one else would appear to need it.

 

What actual uses of projecting waypoints have people used in the field with their GPS?

 

Alan

[+Alan2]

Navdog, I could see from your pix that being off on your projection of a waypoint could make for a bad day geocaching being that close to the canyon rim.

 

I think now I understand what you guys are doing. You give the coordinates to intermediate waypoint "A" to everyone. You then plant the cache at "B" and either walk the distance off from "A" or I suppose measure the distance using your computer and then give that distance as a projected waypoint.

 

Other than for offset geocaching, it doesn't seem to serve any other purpose. I mean if you either walked to the new spot which you would have done if you hid a cache or you used a computer to "see" the new spot. Either way you would know the "projected" coordinates and would give the actual coordinates to anyone who was not playing geocaching. Not much reason for manufacturers to be that accurate to the meter since no one else would appear to need it.

 

What actual uses of projecting waypoints have people used in the field with their GPS?

 

Alan

[+apersson850]

quote:

---

Originally posted by Zartimus(carrdav):

The whole reason I had to do this was the "Hidden Treasure" geocache by Binthair, Quite neat actually and I will not give away the trick in this post. It is 4 inches in diameter so it pays to be right on top of it in the end.

---

 

While it always pays to be on top, think about this analogy:

You want to know the distance between two buildings. They are a little too far away to use the ordinary measuring tape, so you get your hands on a laser ranging unit, capable of measuring the distance down to a few microns (a millionth of a meter). You place the reflector on one of the buildings, then go to the other, and get the distance as 195.472937 meters.

And all this precision achieved, in spite of the fact that you just held the unit in your hand!

 

Now, in your particular case, if you have the starting coordinates given in the popular geocaching format (DD MM.mmm), you know no better than a meter and a half (roughly) where the point is, theoretically. Then you add 3-10 meters of inaccuracy from the GPS position, which usually is a 50% figure, meaning that if you want to be 95% sure that you are within the accuracy circle, you have to double that to 6-20 meters.

 

Then you say you are concerned about being uncertain by five meters, when you have projected the waypoint? When it comes to the final position, these ordinary GPS units aren't like a good dart player. It's more like dart, blindfolded. You'll hit somewhere near, or even on, the board, but not within a few centimeters.

 

I fully agree that there is an unnecessary error introduced here. I'm just trying to make the point, that the error is small compared to everything else.

Meanwhile, a trick is to project two waypoints, one at 190 and one at 200 meter range, then look at your map screen and try to position yourself right between them.

 

Anders

[+apersson850]

quote:

---

Originally posted by Zartimus(carrdav):

The whole reason I had to do this was the "Hidden Treasure" geocache by Binthair, Quite neat actually and I will not give away the trick in this post. It is 4 inches in diameter so it pays to be right on top of it in the end.

---

 

While it always pays to be on top, think about this analogy:

You want to know the distance between two buildings. They are a little too far away to use the ordinary measuring tape, so you get your hands on a laser ranging unit, capable of measuring the distance down to a few microns (a millionth of a meter). You place the reflector on one of the buildings, then go to the other, and get the distance as 195.472937 meters.

And all this precision achieved, in spite of the fact that you just held the unit in your hand!

 

Now, in your particular case, if you have the starting coordinates given in the popular geocaching format (DD MM.mmm), you know no better than a meter and a half (roughly) where the point is, theoretically. Then you add 3-10 meters of inaccuracy from the GPS position, which usually is a 50% figure, meaning that if you want to be 95% sure that you are within the accuracy circle, you have to double that to 6-20 meters.

 

Then you say you are concerned about being uncertain by five meters, when you have projected the waypoint? When it comes to the final position, these ordinary GPS units aren't like a good dart player. It's more like dart, blindfolded. You'll hit somewhere near, or even on, the board, but not within a few centimeters.

 

I fully agree that there is an unnecessary error introduced here. I'm just trying to make the point, that the error is small compared to everything else.

Meanwhile, a trick is to project two waypoints, one at 190 and one at 200 meter range, then look at your map screen and try to position yourself right between them.

 

Anders

[+Navdog]

quote:

---

Originally posted by Alan2:

 

What actual uses of projecting waypoints have people used in the field with their GPS?

---

 

I have also used projected waypoints when exploring new areas on foot. When I have started from a known position, such as along a road, and wanted to walk to a certain feature on a topo map, it is quite simple to measure the distance and bearing on the map and project the waypoint using the GPS. This is much easier than plotting the waypoint on the map with a grid ruler.

 

"I may not have gone where I intended to go, but I think I have ended up where I intended to be."

-Douglas Adams

[+Alan2]

quote:

---

Originally posted by Navdog:

quote:

---

Originally posted by Alan2:

 

What actual uses of projecting waypoints have people used in the field with their GPS?

---

 

I have also used projected waypoints when exploring new areas on foot. When I have started from a known position, such as along a road, and wanted to walk to a certain feature on a topo map, it is quite simple to measure the distance and bearing on the map and project the waypoint using the GPS. This is much easier than plotting the waypoint on the map with a grid ruler.

 

"I may not have gone where I intended to go, but I think I have ended up where I intended to be."

-Douglas Adams

---

 

THat's a good use for it especially if you're not using a mapping GPSr. I could see that being really useful if you're using a non-UTM or gridded map but accurate scalewise or a reduced in size by still scaled map furnished in a local trail guide for instance. Of course with these maps you're not going to be accurate done to the meter anyway so rounding off to the nearest ten meters is about the best you can do. Which is probably one of the reaon the mfr eliminated units in their GPS's. JUst a guess.

 

Anyone else use waypoint projection for non-goecaching uses?

 

Alan

[+Zartimus]

quote:

---

Originally posted by Alan2:

 

If you calculated that at home on a computer, why would you need a Legend to do it for you?

 

Alan

---

 

Save me a trip there and back is all ;-). Arrive at field, take co-ords, go back home, play with map software, go back to field, look for cache.

 

Somone mentioned a few tricks. I liked the idea of placing viual tags for clues, that is cool. And sticking to even numbered distances. I was thinking of making the last two numbers of the co-ords known when one derives the phantom waypoints.

 

I know a WAAS-enabled GPS is looking at a 3m circle on a good day(I've yet to see closer than 4-5m), but I see the inclusion of an extra decimal place of percision as a small thing that I would actually use and appreciate.

 

I shouldn't require a survey capable GPS unit to do a little extra math. I mean the thing can tell me when to FISH!!! Where's my extra decimal place!! (hehehehehe)

[+Zartimus]

quote:

---

Originally posted by Alan2:

 

If you calculated that at home on a computer, why would you need a Legend to do it for you?

 

Alan

---

 

Save me a trip there and back is all ;-). Arrive at field, take co-ords, go back home, play with map software, go back to field, look for cache.

 

Somone mentioned a few tricks. I liked the idea of placing viual tags for clues, that is cool. And sticking to even numbered distances. I was thinking of making the last two numbers of the co-ords known when one derives the phantom waypoints.

 

I know a WAAS-enabled GPS is looking at a 3m circle on a good day(I've yet to see closer than 4-5m), but I see the inclusion of an extra decimal place of percision as a small thing that I would actually use and appreciate.

 

I shouldn't require a survey capable GPS unit to do a little extra math. I mean the thing can tell me when to FISH!!! Where's my extra decimal place!! (hehehehehe)

[+Alan2]

quote:

---

Originally posted by Zartimus(carrdav):

...I shouldn't require a survey capable GPS unit to do a little extra math. I mean the thing can tell me when to FISH!!! Where's my extra decimal place!! (hehehehehe)

---

 

But you only know where to fish down to the nearest 10 meters!

 

Alan

[+Alan2]

quote:

---

Originally posted by Zartimus(carrdav):

...I shouldn't require a survey capable GPS unit to do a little extra math. I mean the thing can tell me when to FISH!!! Where's my extra decimal place!! (hehehehehe)

---

 

But you only know where to fish down to the nearest 10 meters!

 

Alan

[+CharlieP]

My GPS 76 also projects waypoints in 0.1 mile increments, but I have found a better way. I can use the map page MEASURE DISTANCE function to project a point in feet, quick and easy, once I got the hang of it. But I am not sure if the Legend has this function.

 

FWIW,

CharlieP

[Naum42]

I've used projection a number of times in Search & Rescue, and it has come in very handy. There are times we've been sent out in the field with 1 map, and then had our search area changed to another place we didn't have a map for. Base will then sometimes plot us out on their maps, and give us a bearing+distance to get to our new starting point, then sometimes another projection for our ending point. Being able to project that on the GPS is very useful. Being able to project down to the foot would be nice, my Magellan 315 was able to do that if I remember correctly, but my Meridian wont.

 

There is an advantage in projecting points down to 1 foot because it limits your possible error. Since most of the posts I have read today seem to indicate the most accurancy they get is about 4 meters, I'll use that number. If you're projecting from your current GPS location, assuming a max error of 4meters at that time, then project a point that is already 5 meters off, travel there, and have another error of 4 metters you could end up being off by 13 meters. That's not alot, but from what I've seen, 4 meters is fairly good when in dense woods and down in a valley, which is alot of the terrain we search through. Many times we are bushwacking and there are no trails to be found, so it can make a difference.

[Alphawolf]

This is an actual use a customer had in mind while looking for a GPSR that will allow him the accuracy to do this: He is a hunter, and wanted to be able to do the following trick....He is on a hillside and using a laser rangefinder, determines the yardage to big game he has just shot on the opposite hillside of a valley. He wants to be able to project a waypoint to the animal so as to be able to find it easily after traversing down his side, and back up the other side of the canyon, being as the animal will now be out of sight during his trek to it. If a GPSR has only 1 decimal of accuracy, this would put him within 176 yards of the animal (1/10 of a mile is 176 yds)whereas if it does 2 decimals, that gets him within 17.6 yads. I told him that the legend will do this and 17.6 yards is all the accuracy he needs out in the field. If he can't locate the animal within this distance, he needs to stay home!

 

[Idaho Ron]

Alan2,

I use my GPS while hunting for Chukar. These birds are found in canyons up to 800 feet deep. Sometimes I hear them on the other side of the canyon, but there is no way to get there except to drive the long way around. I project a way point to the area the birds are in. Later when I make a hunt to the other side I can go to the projected way points. Since the birds move a lot it doesn't really matter that I am off.

In my Work as a Fish and Game reservist I also use projected way points.

In the spring I go out to catch Sage grouse and we put Radio collars on them. We study them to find out nesting areas and brood raising areas.

A lot of times I see birds fly away from the road and land out in the sage. I project a waypoint to that area so we can have a place to start looking for it later, without going out and bothering the bird right then. Ron

[+Alan2]

I've never heard of a chukar until you mentioned it.

 

chu·kar (che-kär¹) noun

A Eurasian partridge (Alectoris graeca) with grayish-brown plumage and red legs and bill, introduced into western North America as a game bird.

 

[Hindi cakor, from Sanskrit cakorah.]

 

Yours is an interesting use of projecting waypoints. Believe it or not, close by to where I live (Queens NYC one of the five broroughs, I was walking in a local park with a lot of brush by a meadeow lake looking for a cache hiding spot and fliushed a ring-necked partridge which went flying off about 75 yards landing in some fresh brush, squawking all the way. Thought that was the funniest thing a saw a quite a while. Scared the heck out of me. I walked over and flushed him again. He flew back from where he started. It's amazing how many wild birds use NYC and it's flyways as "home" territory. Never did find a spot to hide that cache!

 

Alan

[Idaho Ron]

Alan2,

You will have to forgive me, for being a redneck. I don't think about people on this board from big cities. For instance the county here in Idaho I am speaking of has Over 8000 square miles in it It also has less that 7000 people in it. Just to get there is a two hour drive on dirt roads. The scenery is fantastic. Deep canyons (800 feet deep) And open desert. Here is a picture of the Owhyee Canyon. PS. like I said to get to the other side to find teh projected way point is a 6 hour drive. Ron

[+Alan2]

Looks like some really nice territory out where you live. What's nice about living in a metro area is how nice areas like yours look when I get a chance to travel. It's special when you go to new places where ever they are.

 

Interesting thing though about NYC. Although there's a few more people here than where you live, it really is amazing how many animal and bird species still call this area home. For example, about 5 miles from where I live is a Jamaica Bay Wildlife Refuge part of Gateway National Recreation Area. It's a major flyway and breeding /rest area for the entire East Coast with over 325 species of birds.

 

That’s a great dog you have. Just thinking that my wife wouldn’t appreciate if I trained her poodle Buddy to retrieve. But that would be pretty cool I must admit.

 

http://img.Groundspeak.com/cache/10814_200.jpg

 

Alan

[Alphawolf]

quote:

---

Here is a picture of the Owhyee Canyon

---

I used to do a lot of coyote hunting in the Owhyee Desert North of Winnemucca Nevada and on up towards Boise. You're right! People who have never seen it can't comprehend a hudred miles between ranches! I love it out there. Have you ever fished the Jarbidge?

 

[+gnbrotz]

quote:

---

Originally posted by Alan2:

 

Why would you want to do this? Can you give us a real world example?

 

Alan

---

 

Sure Alan:

A friend and I are establishing coordinates for a particular geographic feature in our area (charcoal hearth site/charcoal terrace). There are over 400 of these sites in a nearby state forest. We have an o-map (1:10,000) which shows their position relative to the landscape, but lacking a lat/lon or UTM grid overlay on the map.

 

We started with a couple close to the road that were simple to find. From there, we use a compass with the map to determine the bearing to the next site we want to visit/get coords for. Measure the distance, plug in the info and project the point. When going from site to site, the gps gives us a straight line to follow. As we are limited to 2 decimal places, we round high and project the line THROUGH the next point. If it's 275 meters away, we project 300. When the gps says were 25 meters from the projected point, we should be able to locate the site. Fortunately, these areas are about 20'-25' in diameter, so most of them are fairly easy to spot. This system works very well for us, although I do wish we could project more precisely.

 

Greg

N 39° 54.705'

W 77° 33.137'

[+parkrrrr]

Part of the problem with projecting more precisely is that the math gets really sticky when you start wanting to use the geodesic of an oblate spheroid instead of a great circle, which is what you have to do to project a waypoint (or even measure a distance) on the surface of the earth with a reasonable degree of accuracy. The difference is small when you're only talking about 300 meters, but over a few miles it can really add up.

 

[+Don&Betty]

Not sure that I really know what this is all about, but if you want to project 475 meters in a particular direction, but your GPSR only permits projecting 470 (0.47 km), how about first pacing off 5 meters in that direction then projecting 470 meters (0.47 km) from there.

[+Alan2]

quote:

---

Originally posted by gnbrotz:

 

We have an o-map (1:10,000) which shows their position relative to the landscape, but lacking a lat/lon or UTM grid overlay on the map.

---

 

Interesting use of wayppoints. Never thought about maps without grids like you're using. But since you're doing this regularly, wouldn't it be helpfulto draw your own grid lines every 1000 meters stating from a rounded off start point. (ie 4567000)Then make it bigger for seeing better it on an enlarger copier. Make up your own grid scale and you have your own UTM map where you can immediately know the UTm location and waypoint that ino your GPS.

 

Your method of extending the waypoint past the point you are going to reminded me of a system I tried out to eliminate "bee dance" when nearing a cache waypoint. When you get at a point that's let's say 50 meters from the cache, stop and project a waypoint let's say .25 kilomweters (or 250 meters) at the bearing to the =cache. Then start walking. When you get to the cache you'll be at .20 but without the bee dancing arrow because the GPS is still looking 200 meters "down the road".

 

Alan

[+gnbrotz]

We actually tried doing this, but given the range of error of a gps, it was hard to do precisely.

 

We have created UTM overlays on clear overhead projection sheets for various scales of maps, but it's difficult to use with the precision we are hoping for. We may dig it out and fool around some more in the future.

 

Greg

N 39° 54.705'

W 77° 33.137'