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GPS coordinates vs. satellite map locations

Last post 08-03-2008, 8:16 AM by mother wolf. 11 replies.
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  •  07-23-2008, 6:58 AM 15038

    GPS coordinates vs. satellite map locations

    I have noticed that the location pinpointed on satellite image maps by the coordinates taken from my GPS do not always match up exactly with where I know I was when I took the reading.  They do seem to be close enough to find the waymark, but it just bothers me a little that the icon does not point to the precise place.  Is this something that is within a normal margin of error for GPS units, or could there be a slightly off alignment of the satellite images with the actual latitude and longitude coordinates?  Also, is it always preferable to post waymarks by the coordinates you personally obtain via GPS, or would it ever be better to get a reading from a map that matches exactly with where I know something is?

  •  07-23-2008, 7:27 AM 15040 in reply to 15038

    Re: GPS coordinates vs. satellite map locations

    While it's certainly not against the basic TOS of Waymarking, numerous category requirements specify that the coordinates obtained for posted waymarks MUST be gotten with a GPSr. It's viewed as "lazy waymarking" or "armchair waymarking" to open up Google Earth and roll your mouse over the general area to get coords. Frankly, if you're there to take a picture, you can grab coords, too.

    In my opinion, the discrepency between the handheld and the desktop software is a good reason to use the handheld. When people are using their handhelds on the site, they don't need the desktop software's coords leading them away from GZ. For waymarks that don't require a handheld to visit, the software's translation of the handheld's coords are good enough because waymarkers are just wanting an idea of where they have to go. But for integrity's sake, the handheld should be used to post the waymark.

     

  •  07-23-2008, 8:33 AM 15042 in reply to 15038

    Re: GPS coordinates vs. satellite map locations

    Some of the problems can me the maps not being properly aligned.  Other problems I have found is in cities with tall buildings where the accuracy of a gps may be very poor.

  •  07-23-2008, 7:54 PM 15052 in reply to 15038

    Re: GPS coordinates vs. satellite map locations

    I usually adjust my coords to the Google Map coords.

    This isn't geocaching, and nobody is going to miss seeing a big building if the coords are a little off.

    I think it looks cool to be able to click into the satellite view picture, and see the object that is being waymarked.

    I would never want to push my opinions on others, though. If you want to pop a coord, and use it as the bible, go for it. I'm into the big picture.

  •  07-30-2008, 9:05 AM 15131 in reply to 15052

    Re: GPS coordinates vs. satellite map locations

    I have found Google Maps to be offset in areas from reality.  When I keep WMs in my GPS that I've made, the GPS is always right... the same cannot be said for GM/GE.

     

    Cool BQ

  •  07-31-2008, 4:07 AM 15151 in reply to 15131

    Re: GPS coordinates vs. satellite map locations

    I agree that I would not trust Google maps, or even the map software that came with my GPSr.  I've found both to be in error at times. I've seen a whole series of waypoints appearing on the wrong side of the street, but the right distance apart.  It is unlikely that is measurement error.

    One issue may be how you are taking the waypoint.  If you just take a single point without giving the GPSr time to adjust to obstructions, you may lose accuracy.  I've found when I jump out of the car to take a waypoint, the accuracy takes a few minutes to increase as the GPSr gathers more data from a wider field of view (without the car roof in the way) and is able to "see" (or is it hear?) more satellites.

    Also, it is best to take an average reading if your GPSr has that function.  I usually set mine down where I want to mark (but not right next to a building, maybe at the curb to improve field of view) and then take my photos as it is averaging.  When I'm done taking pictures, I usually have pretty high accuracy (always <20 ft, but usually <10ft).  That's plenty close for what we are doing.

    I'm not saying you're doing it wrong, just letting you know what works for me.

  •  07-31-2008, 12:33 PM 15158 in reply to 15131

    Re: GPS coordinates vs. satellite map locations

    Personally, I don't trust the google maps coords.

    Fun story:

    My good friend recently moved from NC to just outside of D.C. and I decided to hop on my Honda Shadow to go visit her.  I knew how to get to the town but not to her new home.  She, knowing how attached to my GPS I am, gave me the coords from Google for her house instead of giving me directions from the highway.  We both figured it'd be easier on me and my 2-wheeled transportation to just follow the pointer than to try to read directions and drive, and we were right...in theory.  The coords she got from google, by zooming in on her house, put me 7 miles across town in the middle of the municipal cemetary.  45 minutes, 10 phone calls and what felt like a million 1-way streets later, I finally found her house. 

    So, from my experience, I don't think the Google coords are accurate enough for the purposes of actually finding anything.

  •  07-31-2008, 1:00 PM 15160 in reply to 15158

    Re: GPS coordinates vs. satellite map locations

    I've never seen Google off more than 100 ft or so.

    Sounds to me like a coordinate conversion problem.
  •  07-31-2008, 1:07 PM 15161 in reply to 15160

    Re: GPS coordinates vs. satellite map locations

    Maybe so.  Or a non-GPS user giving coords problem...  I may give Google another try.
  •  08-01-2008, 6:13 AM 15167 in reply to 15161

    Re: GPS coordinates vs. satellite map locations

    yramc600:
    Maybe so.  Or a non-GPS user giving coords problem...  I may give Google another try.

     

    For me another point is "How is the site going to be visited?" and of course the answer in our case should be "By using a GPS unit" so that implies to me that the listing coordinates should be gathered at the site of the Waymark with a GPS unit.

    While I would agree that accuracy is not as critical in Waymarking as it is in other games, it is not true to say that "Meh, close enough" is the right approach either.  At loss for another word, a 'professional' entry attempts to be as accurate as possible whereas a hack-job will leave visitors with the impression that Waymarking is for the lazy.

    Cool BQ

  •  08-02-2008, 5:22 AM 15183 in reply to 15167

    Re: GPS coordinates vs. satellite map locations

    the blue quasar:

    yramc600:
    Maybe so.  Or a non-GPS user giving coords problem...  I may give Google another try.

     

    For me another point is "How is the site going to be visited?" and of course the answer in our case should be "By using a GPS unit" so that implies to me that the listing coordinates should be gathered at the site of the Waymark with a GPS unit.

    While I would agree that accuracy is not as critical in Waymarking as it is in other games, it is not true to say that "Meh, close enough" is the right approach either.  At loss for another word, a 'professional' entry attempts to be as accurate as possible whereas a hack-job will leave visitors with the impression that Waymarking is for the lazy.

    Cool BQ

    I've got a couple of visits under my belt, and I haven't used the GPSer for any of them. I use the map and the pictures to determine I was seeing the same thing the poster intended me to see. Requiring someone to use a GPSer to find a waymark would totally eliminate indoor waymarks.

  •  08-03-2008, 8:16 AM 15198 in reply to 15183

    Re: GPS coordinates vs. satellite map locations

    I'm not 1 for armchair caching in any form: here at WP or geocaching or Terracaching etc. I think it is best if you gps your sites however that being said I am new at this & there are several places I have been & seen that I would like to share with others. If these places were on GC.com then of course I would know what the GPS coords were but if they arent I wouldnt  have the coords. Not having been involved yet in WP I then run into the problem of being able to list them so others CAN maybe visit. Well with diligence I have been able to figure out how to get those coords. Since I am sharing places of interest that are buildings or monuments or geographic sites then 'close' is ok. I include pictures that I have taken when I was there so when you get there you will know by my write up.

    Do I think this is the right thing to do? I think it is ok because I HAVE been there. It was just before I started this. From this point on now I will be able to GPS any site I want to share because I now do this & know to get coords for EVERYTHING I think may be of interest down the road. In fact 1 of the things I now do is along with my little notebook I carry with all the caches Im interested in is I keep a small notebook for any places I visit with coords of all kinds of diffenet locations with notes. (Being an A personality this works for my organizational side LOL) Now I can post up WP's & I have everything I need.

    So GPS vs satillite: since we have this great technology available then if you need to use that I think it's up to each person to decide if its ok for them. MW

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