Best time to hide / find a cache - Really cool web site

Discussion about software such as GSAK, OziExplorer etc, as well as all things hardware, GPSrs, laptops, PDAs, paperless caching, cables etc
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Dik:
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Best time to hide / find a cache - Really cool web site

Post by Dik: » 25 July 12 2:29 pm

Yesterday I was doing some training on advanced DGPS equipment and the subject of PDOP prediction sites arose.

Check out this site: GNSS planning online

Use Pick to select your location by map and the day you intend to hide.

Go to the satellite Library and tick only GPS (unless your GPS can recognise other systems such as GLONASS

Go to DOPs . The lower the figure the better your GPS reading will be. In particular we are interested in the Horizontal position.

If the Dops are getting above 3, you should delay taking your hide co-ordinates.
Remember, this prediction assumes a clear sky. It does not predict errors caused by local obstructions.

You can also view a graph of number of visible satellites, the predicted sky plot as you would see on your GPSr, world view with the satellite paths mapped and an ionosphere map.

Enjoy :D :D :D :D

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GNSS Planning Online

Post by pjmpjm » 26 July 12 2:31 am

Absolutely amazing web site. Thanks.

nutwood
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Re: Best time to hide / find a cache - Really cool web site

Post by nutwood » 26 July 12 2:44 pm

Interesting web-site. Did your course give you any insight as to how critical the correct application of the obstruction curtain is?
For instance, you could pick the best time but if six of your satellites are in the west and there's a large building looming over your west shoulder....? Or does the 10 degree cut-off deal with all but extreme situations?

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Re: Best time to hide / find a cache - Really cool web site

Post by Dik: » 26 July 12 6:04 pm

If you are hiding and know some of the sky is obscured at that location, you can use the PDOP site to assess the sky allowing for the obstruction by sellecting obstructions in the settings page and introduce an obstruction into the calculation by clicking on the sky diagram. This makes big differences to the PDOP chart and helps in selecting an optimum hide time, or times to avoid.

If you are too close to a large obstruction, then an offset may be necessary.
I have personnaly used offsets setting up geocaches, using a compass and tape measure, where the sky view at GZ is marginal or non existant (think 20m down a tunnel or bottom of a cliff).

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Re: Best time to hide / find a cache - Really cool web site

Post by nutwood » 26 July 12 9:09 pm

Is there a quick clever way to apply an offset? I think I can see how you could do it but my method would be a bit clunky.
It's an interesting subject, GPS accuracy. I first got involved with GPS when selective availability was in full swing. That made it interesting trying to get an accurate fix! I used to put fresh batteries in, clear the track log and let the GPS sit; overnight if possible. You'd then look at the track log, stick a pin in the middle of the ball of knitting and hope for the best. I'd like to re-visit some of those locations now and see how accurate they turned out!

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Re: Best time to hide / find a cache - Really cool web site

Post by LouiseAnn » 27 July 12 7:55 pm

what does DOP stand for?

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Re: Best time to hide / find a cache - Really cool web site

Post by Dik: » 27 July 12 10:00 pm

LouiseAnn wrote:what does DOP stand for?
Dilution of Precision.
Don't ask me who framed that term!

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Re: Best time to hide / find a cache - Really cool web site

Post by Dik: » 28 July 12 9:39 am

nutwood wrote:Is there a quick clever way to apply an offset? I think I can see how you could do it but my method would be a bit clunky.!
Hiding,once you have your distance and bearing from a clear location you can project a waypoint using the GPS or your prefered software (eg Garmin map source).

Finding a cache by offset where coverage is bad is a little more tricky. I usually walk a straight line some distance away (along a path or road makes this easier) watching the arrow until GZ is at right angles to the path,and a known distance. Then pace it out.

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