Waypoint Projecting

[+Olar]

I'm considering the projecting of waypoints as part of my next cache. Do all the GPSR's common to Geocaching have this feature?

The following list have it and they are reasonably easy to use:

Magellan:

• 315

Meridian

Map 330 Ver. 2.09

Garmin:

• GPS V

Vista

Yellow Etrex

Venture

II+

12

Map 76

Lowrance:

• Global Map 100

Please post if your's does.

Thanks, Olar

 

 

[This message was edited by Olar on August 07, 2002 at 05:48 PM.]

 

[This message was edited by Olar on August 07, 2002 at 05:53 PM.]

 

[This message was edited by Olar on August 07, 2002 at 05:54 PM.]

 

[This message was edited by Olar on August 17, 2002 at 03:40 AM.]

 

[This message was edited by Olar on August 17, 2002 at 05:14 PM.]

[+park2]

Garmin Vista: Yes

[+Jamie Z]

My Meridian can project a waypoint. One local cacher used that, and projected a waypoint more than 17 miles to the next leg of the cache. I thought it was a bit far, but as it turns out, my projected coords were only off by a hundred yards or so.. and with the clues he gives (although I missed the clues) the second leg isn't hard to find.

 

Jamie

[+Marky]

The first time I learned how was on the multi-cache "A Sunny Day in the Park", which is an awesome day long multi-cache ending with a projected waypoint to the final cache. (As noted before, Magellan Meridians can project waypoints.)

 

--Marky

[+Marky]

The first time I learned how was on the multi-cache "A Sunny Day in the Park", which is an awesome day long multi-cache ending with a projected waypoint to the final cache. (As noted before, Magellan Meridians can project waypoints.)

 

--Marky

[+gnbrotz]

The yellow etrex and the etrex Venture can do this.

 

Greg

N 39° 54.705'

W 77° 33.137'

[+bigeddy]

My old Garmin II+ projects waypoints fine, but the catch is that it uses 1/10-mile increments. When the projection is given in hundreds of feet or sometimes in 1/100-mile increments, that creates a messy situation where I have to figure out how many feet I need to walk before or after the projected waypoint, and how to estimate the feet in cross-country terrain. Combined with the bearing tolerance of a whole degree, that makes the result something of a guess. In such cases, good clues are welcome. If you can, do the projections in 0.1-mile increments.

[gm100guy]

My Lowrance can project a waypoint if I have the bearing and degrees from a start point.

 

 

gm100guy

http://members.rogers.com/gm100guy/cachepage.htm

[gm100guy]

My Lowrance can project a waypoint if I have the bearing and degrees from a start point.

 

 

gm100guy

http://members.rogers.com/gm100guy/cachepage.htm

[+mikemtn]

What if the cache hider projects a way point with his GPSr using magnetic north. I find the clue, 271 degrees, 4/10 mile. If my GPSr is set for true north or I'm trying to use map and compass I'm never going to find it.

 

Back to on topic, I don't think my Garmin GPS 12 will project way points.

 

_______________________________

Mike

 

Never forget, It's just a game.

[+Olar]

quote:

---

Originally posted by mikemtn:

What if the cache hider projects a way point with his GPSr using magnetic north. I find the clue, 271 degrees, 4/10 mile. If my GPSr is set for true north or I'm trying to use map and compass I'm never going to find it.

---

I agree it may be enough of a difference to throw it off. What I would do in the cache description is specify either magnetic or true compass bearings and what differential is used for that area. However if a lot of cachers are like me and cannot remember to add or subtract the differential degrees to convert then I would post both mag and true.

Cheers, Olar

 

[+Olar]

quote:

---

Originally posted by mikemtn:

What if the cache hider projects a way point with his GPSr using magnetic north. I find the clue, 271 degrees, 4/10 mile. If my GPSr is set for true north or I'm trying to use map and compass I'm never going to find it.

---

I agree it may be enough of a difference to throw it off. What I would do in the cache description is specify either magnetic or true compass bearings and what differential is used for that area. However if a lot of cachers are like me and cannot remember to add or subtract the differential degrees to convert then I would post both mag and true.

Cheers, Olar

 

[+parkrrrr]

Mine (Palm Vx with Magellan GPS Companion for Palm V) does not. I've been complaining about that forever, though, so it shouldn't surprise anyone here.

 

However, it's often possible to work around a limitation like that. For example, you can always compute the back bearing and then walk until your GPSr tells you that the distance and bearing to where you started are equal to the back bearing and distance you're looking for.

 

[+EraSeek]

Add the Garmin 12 and Map76 to your list of ''do's''

 

[+LaPaglia]

Navman/Ipaq 3635 with OziExplorerCE does not. At least not yet.

 

Lapaglia

"Muga Muchu" (forget yourself, focus).

[+LaPaglia]

Navman/Ipaq 3635 with OziExplorerCE does not. At least not yet.

 

Lapaglia

"Muga Muchu" (forget yourself, focus).

[+mikemtn]

quote:

---

Originally posted by EraSeek:

Add the Garmin 12 and Map76 to your list of ''do's''

 

---

 

I've lost my instructions but looking at the downloaded instruction book I can't see how to do it. Reference waypoints the same thing? It don't want to come out right. Please help.

 

_______________________________

Mike

 

Never forget, It's just a game.

[+sledgehampster]

Add the Magellan MAP 330 to the "DO" list if one upgrades it to Firmware ver. 2.09.

[+DarrenF]

The eTrex Legend (and I presume Vista) can project waypoints. But there are of course some limits as to the precision which a projected waypoint can be placed.

 

If the units are set to miles, the distance is entered to the nearest .01 mile (about 53ft), if the units are set to metric, the distance is entered to the nearest .01 km (about 33ft).

 

The bearing must be entered in integer degrees (I haven't played with it much, but I think this is the only input format for the bearing, no matter what the settings).

 

So projected waypoints can be placed any of the 360 equidistant points points on a circle any multiple of 52.8ft (10m, if using metric) from a given waypoint, clearly the further away from the waypoint, the further apart these possible point become--e.g. at 1 mile away, they are about 92 feet apart.

 

df

[+Byron & Anne]

quote:

---

Originally posted by Warm Fuzzies - Fuzzy:

Mine (Palm Vx with Magellan GPS Companion for Palm V) does not. I've been complaining about that forever, though, so it shouldn't surprise anyone here.

 

However, it's often possible to work around a limitation like that. For example, you can always compute the back bearing and then walk until your GPSr tells you that the distance and bearing to where you started are equal to the back bearing and distance you're looking for.

 

http://216.202.195.127/warm.gif

---

 

I found a little program that will do this called NavCalc. You can get it from palmgear.com. I think it was $10.00. It's slow but seems to work ok.

 

Byron

[+DarrenF]

Converting a bearing & distance to a latitude & longitude offset is fairly straightforward:

 

latitude offset (in decimal minutes) = distance (in nautical miles) * cos(bearing)

 

longitude offset (in decimal minutes) = distance (in nm) * sin(-bearing) / cos(latitude)

 

note: 1 nm = 6076ft

 

The above assumes you are near sea level, the earth is a sphere, and probably break down near the poles... and should be checked by someone not doing math by the seat of his pants before being used

 

df

[+DarrenF]

Converting a bearing & distance to a latitude & longitude offset is fairly straightforward:

 

latitude offset (in decimal minutes) = distance (in nautical miles) * cos(bearing)

 

longitude offset (in decimal minutes) = distance (in nm) * sin(-bearing) / cos(latitude)

 

note: 1 nm = 6076ft

 

The above assumes you are near sea level, the earth is a sphere, and probably break down near the poles... and should be checked by someone not doing math by the seat of his pants before being used

 

df

[+apersson850]

quote:

---

Originally posted by DarrenF:

 

The bearing must be entered in integer degrees (I haven't played with it much, but I think this is the only input format for the bearing, no matter what the settings).

 

So projected waypoints can be placed any of the 360 equidistant points points on a circle any multiple of 52.8ft (10m, if using metric) from a given waypoint, clearly the further away from the waypoint, the further apart these possible point become--e.g. at 1 mile away, they are about 92 feet apart.

 

df

---

This isn't true. If you set the GPS to mils as the unit for bearings, you can set any of 6400 directions. One mile away, these points are 2.6 feet apart. Or 0.79 meters. One kilometer away, they are .49 meters apart. Since the resolution along the radii (do you say so in English?) is 10 meters, you have to be 20372 meters away to have the same resolution in both directions.

 

Anders

[+DarrenF]

quote:

---

Originally posted by Anders:

This isn't true. If you set the GPS to mils as the unit for bearings, you can set any of 6400 directions. One mile away, these points are 2.6 feet apart. Or 0.79 meters. One kilometer away, they are .49 meters apart. Since the resolution along the radii (do you say so in English?) is 10 meters, you have to be 20372 meters away to have the same resolution in both directions.

 

Anders

---

 

Excellent observation. This is why I keep returning to these forums I learn something new every day.

 

However, I calculate the points to be about 5.1ft ( 1.58m) apart at 1 mile (1.61km) distant; and .98m apart at 1km distant. I used arclength=r*theta, and calculated that 1mil * 2*Pi radians/6400mils = .000982 radians. I realize the arclength isn't the shortest distance between the two points, but it should be pretty close, especially as the radius increases.

 

So in summary, the best resolution for projecting a way point is obtained by setting the bearing to mils (Setup Menu|Heading|Display) and the distance to metric (Setup Menu|Units|Distanct/Speed).

 

PS-radii is perfectly correct in English; I never would have guessed English isn't your first language.

 

df

[+DarrenF]

quote:

---

Originally posted by Anders:

This isn't true. If you set the GPS to mils as the unit for bearings, you can set any of 6400 directions. One mile away, these points are 2.6 feet apart. Or 0.79 meters. One kilometer away, they are .49 meters apart. Since the resolution along the radii (do you say so in English?) is 10 meters, you have to be 20372 meters away to have the same resolution in both directions.

 

Anders

---

 

Excellent observation. This is why I keep returning to these forums I learn something new every day.

 

However, I calculate the points to be about 5.1ft ( 1.58m) apart at 1 mile (1.61km) distant; and .98m apart at 1km distant. I used arclength=r*theta, and calculated that 1mil * 2*Pi radians/6400mils = .000982 radians. I realize the arclength isn't the shortest distance between the two points, but it should be pretty close, especially as the radius increases.

 

So in summary, the best resolution for projecting a way point is obtained by setting the bearing to mils (Setup Menu|Heading|Display) and the distance to metric (Setup Menu|Units|Distanct/Speed).

 

PS-radii is perfectly correct in English; I never would have guessed English isn't your first language.

 

df

[+apersson850]

My mistake. I calculated the circumference as pi*radius, not pi*diameter. So my figures are optimistic by a factor of two. Sorry, but I'm at work, and supposed to think about other, perhaps more important (or, no??) things...

 

Don't believe what I posted, except that mils is the angular mode with highest resolution.

 

Thanks for the comments about my English. My old teachers will smile proudly, I assume.

 

Anders

[+apersson850]

My mistake. I calculated the circumference as pi*radius, not pi*diameter. So my figures are optimistic by a factor of two. Sorry, but I'm at work, and supposed to think about other, perhaps more important (or, no??) things...

 

Don't believe what I posted, except that mils is the angular mode with highest resolution.

 

Thanks for the comments about my English. My old teachers will smile proudly, I assume.

 

Anders