+RobAGD Posted January 11, 2015 Share Posted January 11, 2015 Well, I have to first say LTNS for a lot of you I have a small project I was working on for work. I was way pointing new items we had build and looking to over lay that into Google Maps. I started with my Phone ( Note 2, Note 4 and a ASUS Transformer Tablet ) and a few different apps. Under clear open sky getting a ton of satellites I am just not seeing the accuracy that I am use to from my Garmin V. I routinely recall getting sub 3ft accuracy or better when doing Waypoint averaging. With my Phones/Tablet I cant get with in 20-40ft I am using HandyGPS atm which has averaging, an it shows sub meter, but in reality that is not quite right. I have been using 3 known points to triangulate my new points, its off at least 7 meters. I dug out my old V and got it running, but it wasn't pulling better than 40ft on the drive to work. So first - Did the accuracy go down at some point ? Next I am sure there has been a massive improvement in PC side software. What may work for what I am looking to do, is if I could drag a layer of waypoints to match know points. Is there a tool out there that would allow for something like this ? Suggestions other than buying a dedicated GPS unit, unless you can point me to something that would be cheap and get me sub 1ft accuracy Danke ! -Robert Quote Link to comment
+T.D.M.22 Posted January 11, 2015 Share Posted January 11, 2015 (edited) Well to start off, you're not talking about accuracy. It's actually an estimated potential for error. That means if you're seeing 12 feet, it may be up to 12 feet off, not is definitely 12 off. You really shouldn't worry until it's more than 10m/30 feet. Part of that reason is that if you get it within millimetres, that will not help at all if my GPS is off that day. You also mentioned Google maps- well the problem with that us that it's multiple pictures stitches together. It's not meant to be a location device to replace a GPS so there will be errors. When you plug in co-ords they may show as being in a different location. It's different for different providers, even different map types from the same provider. Plus the earth is round, maps are not, so there is some error I just changing the shape. Long story short, you're fine with what you have. Edited January 11, 2015 by T.D.M.22 Quote Link to comment
+RobAGD Posted January 11, 2015 Author Share Posted January 11, 2015 While I understand averaging, the issue is these point need to be within a meter. To give you an idea I am working with this as my base. I am marking newly build "bunkers", towers and staging areas. By using known points on the map it gives me my margin, which if I could take all the way points and manipulate them as a layer, I could get them more inline with where they phycially are on the field. as an example : 2 of the 3 points I use for checking location are off almost the same distance. The 3rd is also off the same amount but it is off the screen in this shot. This actual ending coords are not that important, location on the MAP is more what I am worried about. Thanks for the thoughts and suggestions. -Robert Quote Link to comment
+Mineral2 Posted January 11, 2015 Share Posted January 11, 2015 you might need survey-grade equipment if you need to be that accurate. Quote Link to comment
+GeoTrekker26 Posted January 11, 2015 Share Posted January 11, 2015 While I understand averaging, the issue is these point need to be within a meter. This actual ending coords are not that important, location on the MAP is more what I am worried about. -Robert You say you need to be within a meter then you say the coords don't matter. Which is it? You talk about "By using known points on the map.." How were these points determined? If by using consumer grade GPS equipment then they are not known points. You are asking consumer grade equipment to do things it can't. It's like trying to measure the thickness of a hair with a yardstick; it isn't going to work. Quote Link to comment
+Gitchee-Gummee Posted January 11, 2015 Share Posted January 11, 2015 If you really need RELIABLE readings, mineral2 is correct in that you should be using survey-grade equipment. You already know that a stand-alone commercial-grade GPSr is better, but you use a multi-use device and expect better? ...cheap and get me sub 1ft accuracy I don't see this statement as having any possibility of ever happening. Quote Link to comment
+splashy Posted January 11, 2015 Share Posted January 11, 2015 (edited) The accuracy of a gps receiver is a calculation of variables received from the satellites. Where nothing is really sure because of bad weather/power lines/transmitting towers or signals bouncing (multipath). The EPE - estimated position error is just an indicator. Second, who says the map you are using is really accurate? Even if it's GE. BUT if you really averaged the waypoints these waypoints might have the right coordinates even if they show up on the 'wrong' place of the map. Many people believe the Gps is accurate to the few feet, because of the car Sat Navs, where software puts the position of the 'cursor' always right on the road. Edited January 11, 2015 by splashy Quote Link to comment
+MartyBartfast Posted January 11, 2015 Share Posted January 11, 2015 You say you need to be within a meter then you say the coords don't matter. I took that to mean that the absolute co-ords (i.e. exactly where on the surface of the earth they resolve to) don't matter, but the relative co-ords (i.e. this bunker is exactly x feet from it's neighbour, which is on a bearing of xxx degrees) do matter. If so I wonder if he could achieve it by implementing his own version of differential GPS correction? Set up a number of fixed points, e.g. at each corner of the plot and by taking averaged readings at each establish them as known points and record their co-ords. Then each day you go to take readings you take readings of these points first, if the co-ords you get are off by 3 feet from the "known" position then you correct each reading you subsequently take by 3 feet, if the next day the fixed points are 5 feet out, then you apply a correction of 5 feet to all readings you take. I don't know how accurate this could be, and it would need some fancy maths applied to each pair of co-ords to correct not just the distance but also the bearing. Even if it did work I can't honestly see it being worth the (significant) effort. Quote Link to comment
alandb Posted January 11, 2015 Share Posted January 11, 2015 (edited) According to Garmin ... How Accurate is GPS? 08/29/2007 Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters (49 feet) 95% of the time. Generally, users will see accuracy within 5 to 10 meters (16 to 33 feet) under normal conditions. https://support.garm...000000000000%7D Also ... How can WAAS help me achieve better accuracy? 08/29/2007 Garmin GPS receivers with WAAS (Wide Area Augmentation System) capability can improve accuracy to less than 3 meters (10 feet) on average. https://support.garm...000000000000%7D Edited January 11, 2015 by alandb Quote Link to comment
+RobAGD Posted January 12, 2015 Author Share Posted January 12, 2015 Marty, you are correct, with 3 or 4 markers with a known points on my map, if I could correct based off the difference. It doesn't need to spot on but relative to each other. Each waypoint batch always seems to have a consistent offset vs the "known" points. Yes I know the MfDs have a different priority than single purpose devices. But I found out odd that within an app I get X accuracy (calculated) them in a GPS tool I felt a different number. I recall the figured accuracy when I was actively caching that my V for outstanding as long as I wasnt in a steep walled Valley. I was more Wonderin if Something may have changed in my absence from caching, I was also wondering about a map / waypoint software. My remark about the survey was more sarcasm as I know those units are expensive as sin. I do appreciate the replies. -Robert PS sorry if this is formatted oddly doing this on my phone and the forum software was causing some issues. You say you need to be within a meter then you say the coords don't matter. I took that to mean that the absolute co-ords (i.e. exactly where on the surface of the earth they resolve to) don't matter, but the relative co-ords (i.e. this bunker is exactly x feet from it's neighbour, which is on a bearing of xxx degrees) do matter. If so I wonder if he could achieve it by implementing his own version of differential GPS correction? Set up a number of fixed points, e.g. at each corner of the plot and by taking averaged readings at each establish them as known points and record their co-ords. Then each day you go to take readings you take readings of these points first, if the co-ords you get are off by 3 feet from the "known" position then you correct each reading you subsequently take by 3 feet, if the next day the fixed points are 5 feet out, then you apply a correction of 5 feet to all readings you take. I don't know how accurate this could be, and it would need some fancy maths applied to each pair of co-ords to correct not just the distance but also the bearing. Even if it did work I can't honestly see it being worth the (significant) effort. Quote Link to comment
+MartyBartfast Posted January 12, 2015 Share Posted January 12, 2015 I recall the figured accuracy when I was actively caching that my V for outstanding as long as I wasnt in a steep walled Valley. I was more Wonderin if Something may have changed in my absence from caching, I was also wondering about a map / waypoint software. I think your memory may be playing tricks on you, maybe it was 3 yards you used to get rather than 3 feet? As far as I know no consumer grade GPS has ever claimed better than ~10 feet (e.g. my current device), and I know the Etrex I used when I started claimed 30 feet, and my experience has reflected this degree of improvement. Not too sure about the accuracy of phones etc as although I have used them for their GPS it's only ever been occasional use. Quote Link to comment
+RobAGD Posted January 12, 2015 Author Share Posted January 12, 2015 Marty - from my reading the GPS's in Phones/Tablets are more worried about fast acquisition time than accuracy. Which is why I think that each waypoint group looks to be a bit off consistently for the group. Something else I noticed when I am avg out a waypoint that the first 3 are flyers then the next 10-15 points are much closer/clustered. -R Quote Link to comment
+RobAGD Posted January 15, 2015 Author Share Posted January 15, 2015 So while googling I found some interesting blog post from a guy that does GSI style work using a Trumbull antennas on his Nexus 4. He did a couple of blog posts that cover the a couple of interesting tidbit he did find so here are some links. Http://www.tristate-engineering.com/ideas-gis/archives/04-2013 Along with the May blog post. -Robert Quote Link to comment
+ecanderson Posted January 16, 2015 Share Posted January 16, 2015 (edited) Don't get hung up on the idea that the phone mattered. It wouldn't have mattered what he connected the Trimble 'antenna' to .. because it's not really an 'antenna'. It's an entire GPSr system. He was then sending the coordinate data to his phone via Bluetooth for display/storage/whatever. Edited January 16, 2015 by ecanderson Quote Link to comment
+splashy Posted January 16, 2015 Share Posted January 16, 2015 (edited) Often an answer in a forum is not what you want to hear, therefore it's not considered as a good or relevant answer. A consumer gps is what it is and the only way to get a reading more accurate is to average your waypoint, that takes time but it won't get any better. Maybe a cluster of waypoint are off, because they where shielded, then even averaging doesn't help. Edited January 16, 2015 by splashy Quote Link to comment
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