The degree of closeness of measurements of a quantity to that quantity's actual value

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181
votes
5answers
142k views

How to measure the accuracy of latitude and longitude?

I am very new to GPS stuff. Suppose I have latitude and longitude as 19.0649070739746 and 73.1308670043945 respectively. In this case both coordinates are 13 decimal places long, but sometimes I also ...
38
votes
2answers
4k views

How accurate is approximating the Earth as a sphere?

What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them. Are ...
10
votes
3answers
7k views

How does ArcGIS compute the distance between two points with a non-equidistant projection?

This is a follow-up question to my previous one, Can you suggest some well-written introductory texts about coordinate system projections? Let's assume I'm working with the CH1903 map projection, ...
24
votes
5answers
38k views

What is the maximum Theoretical accuracy of GPS?

I was talking with a potential client, and they requested that we plot some points with GPS, with a maximum (or should that be minimum?) accuracy of 2 m. This is an area with no WAAS, and I was under ...
9
votes
3answers
14k views

Generally accepted root mean square (RMS) error for rectifying topographic maps

This is a generic inquiry on the common practice/standard for determining the acceptable values of RMS when georeferencing topographic maps. Is there an absolute value? Some literature suggests that ...
3
votes
1answer
1k views

Google Earth, Google satellite, and Bing aerial accuracy

Does anybody know the accuracy of Google Earth, Google satellite, and Bing aerials, and at what scale? I think that you have different/better accuracy if you have subscribed to their professional ...
36
votes
12answers
30k views

Tablet or smart phone GPS vs “real” GPS

I've been reading a lot today about android and iphone devices being used for spatial data collection in the field and it sure seems to be that single purpose devices such as the extremely popular ...
22
votes
6answers
5k views

How correct is the “Accuracy” value given by GPS devices?

I have a Garmin Forerunner 305 and a Google Nexus One Android phone. From the GPS on both these devices I can get a "Accuracy" value that is usually between 6-20 meters. How much can I trust this ...
14
votes
2answers
2k views

How much sense does it make to average (lat,lon) samples in order to increase 2D accuracy of a GPS location?

Several GPS applications, like this one, or this one, acquire multiple (lat,lon) samples of a given location, assuming that the GPS unit is not moving, and then take an average of the samples in order ...
2
votes
0answers
479 views

How to use QGIS Accuracy Assessment plugin? [closed]

I am new user and i want perform accuracy assessment in qgis. I have 1 classified map and another for validation. I have installed the plugin. what am i doing after? Plugin: ...
13
votes
3answers
1k views

GPS Elephant Tracking: Utilizing A-GPS, WAAS, DGPS and Understanding HDOP, NSAT, and ZDA

*I'm using a GPS data logger (qstarz bt-q1000xt) to track the movement of zoo elephants, and I have a variety of technical questions. I've had limited success receiving answers from the vendor. You ...
5
votes
2answers
336 views

Spatial interpolation - appropriate method to estimate the accuracy of the surface

When using a spatial interpolation method (any method) without having a way to validate it, besides sampling some points out, is there a way to count as well with the mean distance between ...
6
votes
1answer
785 views

Need to learn more about Precision and Accuracy

I am currently taking Introduction to Image Interpretation online and there is a section in it that talks about Precision and Accuracy. I wanted to know if someone out there has any good information ...
5
votes
1answer
501 views

If the GPS navigation message takes 12 1/2 minutes to cycle, how can receivers update your position every second?

According to Wikipedia's article on GPS, Each GPS satellite continuously broadcasts a navigation message... Each complete message takes 750 seconds (12 1/2 minutes) to complete. My ...
2
votes
2answers
833 views

How to perform an accuracy assessment in eCognition?

How to do accuracy assessment of classified images in ecognition? I have done the image segmentation for Worldview-2 image. Then, I have processed for classification for class names (e.g ...
2
votes
1answer
458 views

How do you calculate positional accuracy in qgis?

How to you compare two layers in QGIS to get the positional accuracy?
9
votes
2answers
8k views

How accurate are measurements in Google Earth?

Can anyone point to a resource that lists the accuracy of measurements taken in Google Earth?
2
votes
1answer
9k views

How accurate is the google maps latitude and longitude I am using?

I am making a program that uses GPS location preferably from smart phone, laptop works too and compares it to a building, the points you in its general direction. I am making this web application ...
1
vote
0answers
475 views

Collector for ArcGIS PDOP and GPS collection configuration settings

My company just acquired a Geneq SXBlue II GPS receiver to pair with an iPad and the Collector for ArcGIS app. The functionality is awesome and loved by everyone, but since we have biologists on our ...
1
vote
1answer
142 views

What sub-meter geolocation solutions exist and how can I integrate them into a web and mobile mapping workflow?

I am the manager of seven water systems. What I am trying to do is map out every meter and valve on to a map and then my workers can have the maps on their iPhones so when they have to go fix a water ...