+tjpratt Posted July 26, 2014 Share Posted July 26, 2014 I did do some searches to no avail. Live in Spokane lotsa Basalt around. GarminGPSmapsc (not "real" familiar with it). When using my compass to search is this rock messing me up??? Thanks Quote Link to comment
+Viajero Perdido Posted July 26, 2014 Share Posted July 26, 2014 You don't need a compass to find caches. Rocks don't interfere with GPS signals. With a compass, maybe, but like I said, you don't need a compass. Good luck. It should get easier over time. Quote Link to comment
+tjpratt Posted July 26, 2014 Author Share Posted July 26, 2014 You don't need a compass to find caches. Rocks don't interfere with GPS signals. With a compass, maybe, but like I said, you don't need a compass. Good luck. It should get easier over time. Quote Link to comment
+tjpratt Posted July 26, 2014 Author Share Posted July 26, 2014 I like using the compass But if you say "Basalt" doesn't interfere with a compass...well, I will hang tight here for a few more thoughts. Thanks Quote Link to comment
+Ambrosia Posted July 26, 2014 Share Posted July 26, 2014 I don't understand gpsrs, but we seem to have problems with rocks, too, especially basalt columns and canyons and such. We have a cache that is placed at the base of a basalt cliff, and we can't get the coords down to anything less than 100 feet. No one can ever find the darn cache, so I don't know what the point of it is. Quote Link to comment
+Gitchee-Gummee Posted July 26, 2014 Share Posted July 26, 2014 (edited) Basalt has no minerals with which to interfere with a compass. Iron ore, in its' many forms including magnetite and hematite, can lead (magnetic) compasses astray. EDIT to add: That was how the iron ore deposits were discovered in Michigan and Minnesota. The original surveyors had much difficulty with their compasses. Edited July 26, 2014 by Gitchee-Gummee Quote Link to comment
+MartyBartfast Posted July 26, 2014 Share Posted July 26, 2014 Just to clarify, anything which gets between your GPS and the sky will affect the GPS reception, whether it's basalt, chalk, sandstone, or the roof of your house. So if you're standing at the foot of a cliff, just look around you and your GPS can't get a signal from the satellites in that part of the sky which you can't see because the cliffs are in the way, so I would guess the cliffs are obscuring ~40% of the satellites. If you're in a canyon then there's probably ~%80 of the sky obscured. The makeup of the cliffs in these situatuations is irrelevant, but they will affect the reception. For the OP question I was taking him to mean he was walking around on top of Basalt rocks, which won't affect the GPS signal. Quote Link to comment
+Ambrosia Posted July 26, 2014 Share Posted July 26, 2014 Just to clarify, anything which gets between your GPS and the sky will affect the GPS reception, whether it's basalt, chalk, sandstone, or the roof of your house. So if you're standing at the foot of a cliff, just look around you and your GPS can't get a signal from the satellites in that part of the sky which you can't see because the cliffs are in the way, so I would guess the cliffs are obscuring ~40% of the satellites. If you're in a canyon then there's probably ~%80 of the sky obscured. The makeup of the cliffs in these situatuations is irrelevant, but they will affect the reception. For the OP question I was taking him to mean he was walking around on top of Basalt rocks, which won't affect the GPS signal. Sure, that makes sense. You have that problem being around buildings, too, like downtown Manhattan. Quote Link to comment
+niraD Posted July 26, 2014 Share Posted July 26, 2014 When you're near a cliff, near a big building, in a canyon, etc., another thing that can happen is that your GPS receiver may pick up a satellite signal that has been reflected off the rock surface or off the side of a building. These multipath errors can introduce fairly large errors into your device's calculations. Quote Link to comment
+tjpratt Posted July 26, 2014 Author Share Posted July 26, 2014 (edited) Thank you ALL for taking the time and the info.As I mentioned I am using...GarminGPSmapsc this GPS. Should I just assume that if it gets me within lets say 10' I should start using my EYES, along with the hints and Logs. Edited July 26, 2014 by tjpratt Quote Link to comment
+K13 Posted July 26, 2014 Share Posted July 26, 2014 You should start using your eyes within about 30 feet. If the device placing the cache was 10-15 feet different from your device reading, that would allow for a up to a 20-30 foot variance. Variance in the satellite patterns and signals at different times can cause this much of difference in readings. Quote Link to comment
+Walts Hunting Posted July 26, 2014 Share Posted July 26, 2014 What you are describing is common in rock areas even who they are all on the ground and not in any way obscuring the signal. It is called multi path and here is a good explanation. http://www.trimble.com/gps_tutorial/howgps-error2.aspx Quote Link to comment
4wheelin_fool Posted July 27, 2014 Share Posted July 27, 2014 What you are describing is common in rock areas even who they are all on the ground and not in any way obscuring the signal. It is called multi path and here is a good explanation. http://www.trimble.com/gps_tutorial/howgps-error2.aspx That's the same thing that Nira mentioned in post #9 and explains a lot of what I've noticed. The only other way that basalt can interfere with a compass is from a gravity induced impact. Quote Link to comment
+Walts Hunting Posted July 27, 2014 Share Posted July 27, 2014 What you are describing is common in rock areas even who they are all on the ground and not in any way obscuring the signal. It is called multi path and here is a good explanation. http://www.trimble.com/gps_tutorial/howgps-error2.aspx That's the same thing that Nira mentioned in post #9 and explains a lot of what I've noticed. The only other way that basalt can interfere with a compass is from a gravity induced impact. I love the gravity induced impact as a method of interference. Quote Link to comment
+humboldt flier Posted July 27, 2014 Share Posted July 27, 2014 I did do some searches to no avail. Live in Spokane lotsa Basalt around. GarminGPSmapsc (not "real" familiar with it). When using my compass to search is this rock messing me up??? Thanks Hey there, Be careful in those basaltic flows: a Spokane Area Cacher fell to his death a few years back Quote Link to comment
+CdAGeoGeeks Posted July 29, 2014 Share Posted July 29, 2014 Welcome to caching in Spokane! You should come to an event and meet some of the locals if you haven't done so already! There are several cachers in the area who enjoy sharing different experiences. Quote Link to comment
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