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How Do You Project?


Navdog
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I have several multi-caches that require waypoint projections. I am a big fan of having navigational elements in caches. Unfortunately my GPS V does not allow projections under .10 mi. and then only in 1/10 mi. increments. There are several ways to get around this problem, but I was wondering how others project waypoints. It would also be nice to hear which GPS units specifically allow projections under .10 mi. I know my Vista does, what about other units?

Edited by Navdog
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For what it's worth, I've made the source code to GeoCalc freely available (GPL). It's written in C++. And the calculation part of the code is platform-independent. I've run it on Linux and MacOS as well as the PC. So if anybody has a PalmOS compiler and wants to make a free program for the Palm, I would be more than happy to help.

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I have a cache that uses projections. It's called "Play it Safe!".

 

One way you can do projections is by using the GOTO function. If you need to find a waypoint that is 1.35 miles from your current location at a bering of 180 degrees, then all you would do is start walking south (180 degrees) from your current location, making sure your BEARING (back to your starting point) remained at 0 degrees (the opposite direction). When the distance reading on your GPS reads "1.35 miles", and the bearing reads "0 degrees" then you would be at the projected waypoint. It's geocaching in reverse!

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I have the Lowrance gm100 and it allows you to 2 decimal places when using kilometers. So that would be 10 meter projection. Don't think I would need to go lower then that.

 

Did you try kilometers on your unit for distance, it might go lower in that unit of measure.

 

:huh:

Edited by gm100guy
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For short distance, it may be just as easy to convert your current position to UTM (most GPS receivers will do the conversion for you). Then, if you know the bearing and distance (in meters), simple trig calculations will get you the northing and easting offsets to the final position. Add the offsets to the current location and then convert back to Lon/Lat.

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I have been wondering how u project waypoints exact enough to hide the geo's that you do?????? My old GPS did not project waypoints. We always marked our current waypoint as home, then we used our compass to get us going in the correct direction, and then stopped when our gps as said we had gone far enough (that is we are now Xfeet away from where we started, kind-of a reverse goto). I am very interested to find out if there is a better or more exact way to do this?????

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It would also be nice to hear which GPS units specifically allow projections under .10 mi. I know my Vista does, what about other units?

With the MeriPlat you can project to less than one foot.

How many decimal places is less than a foot? A difference of .001 is normally between 4.5 and 6 feet.

Edited by CO Admin
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I set my gps to kilometers so that waypoint projection is in tenths of a kilometer. Then , when I get within 100 metres, I carefully take a sighting of all features along the last stretch along which the cache is located. Then I record a landmark and walk to one of the features. When the numbers are right, I start looking for the cache. like this:

 

To project a waypoint 253 meters. First project 200 meters. When you get there, stop, record landmark of your current position. Now project a further 100 meters at the same bearing. Look for landmarks along your

projected path. Go to the landmarks one by one until you read 53 meters from your last recorded position. Then start searching.

 

It has always worked for me.

Edited by BeDoggy
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I have been wondering how u project waypoints exact enough to hide the geo's that you do?

A “reverse GOTO” is pretty much my way of figuring projected waypoints, especially those under .10 mi., which most GPSr’s start measuring by the foot. All you need to do is figure the reciprocal bearing and walk the specified distance. It is best to let your GPS settle down at the reference point before you mark your spot for a projection. It is also better to use a new set of coordinates for your starting point, than to rely on the coords given by the hider. Your coords account for the satellite PDOP at the current time you are doing the cache, and not the PDOP of the hider when they placed the cache weeks ago. This assures you that when you reach the other end of your projection you will have better accuracy. Pulling away from the trunk of a tree 5-10 feet along a north/south axis may help your reception, just be sure to account for this on the other end or readjust your coords before heading towards the other end of your projection.

 

When I do line of sight projections, I use my Suunto optical hand bearing compass. Looking through the eyepiece gives me ½ degree accuracy for the bearing line, then I walk off the distance and compare that to the GPS reading for distance. Knowing what your stride distance is can be very accurate. This may not help the cacher without a manual compass, but it ensures me that my projection is correct.

 

GPS projections are inherently more unstable at shorter distances with poor satellite geometry. If you can do a line of sight reading with a good sighting compass you will get better results.

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It would also be nice to hear which GPS units specifically allow projections under .10 mi. I know my Vista does, what about other units?

With the MeriPlat you can project to less than one foot.

How many decimal places is less than a foot? A difference of .001 is normally between 4.5 and 6 feet.

First I enter.01 and hit the enter button. Now it changes to feet and you can edit that. 0.82 ft. was the lowest I was able to save it.... as if I really need to project a waypoint under my toes :D

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It would also be nice to hear which GPS units specifically allow projections under .10 mi. I know my Vista does, what about other units?

With the MeriPlat you can project to less than one foot.

How many decimal places is less than a foot? A difference of .001 is normally between 4.5 and 6 feet.

First I enter.01 and hit the enter button. Now it changes to feet and you can edit that. 0.82 ft. was the lowest I was able to save it.... as if I really need to project a waypoint under my toes :D

That's pretty cool! Kinda overkill though, but nice to know.

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With the MeriPlat you can project to less than one foot.

How do you do that with the MeriPlat? I just got one and it only seems to allow me to enter in miles (or kilometers) to 2 decimal places, which is about 52 ft or 10 meters. Is there something I need to change in the setup? :D

 

Edit: Oops - didn't read far enough. Very cool. :D Thanks!

___________

Gorak

Geo 26A

Edited by Gorak
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This is pretty COOL! After Warriorrider mentioned the Meridians allow projections down to the 1/10 foot, I was playing around with my GPS V and found when you have the distance field highlighted for your projection distance, if you scroll over and highlight the default "mi." display to the right of the number field, and press the menu button, it allows you to change the setting from miles to feet! So you can enter 000.0 feet to 999.9 feet for a projection. Something the manual doesn't mention and makes projections much easier. :D

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And, something you can do if your GPS doesn't do projections on the fly:

 

Let's assume you're standing at point A and want to go to point B, and all you know is that it's 1500 feet away on a bearing of 112°. What you do is mark a waypoint at point A, and set that as your GOTO point. Then, walk in a generally east-southeasterly direction, trying to keep the bearing to your GOTO point as close to 292° as possible. (292 is 112+180. In general, if the bearing you want is more than 180°, subtract 180; otherwise, add 180.) When the distance reaches 1500 feet and the bearing is 292°, you're in about the right place.

 

Note, though, that projections of more than a few hundred feet are unlikely to work, unless you can force your GPS to display the distance in feet. The Magellan Nav Companion software for Palm, for example, switches from feet to miles at 528 feet.

Edited by parkrrrr
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