92

Here's my rule of thumb table... Latitude coordinate precision by the actual cartographic scale they purport: Decimal Places Aprox. Distance Say What? 1 10 kilometers 6.2 miles 2 1 kilometer 0.62 miles 3 100 meters About 328 feet 4 10 meters About 33 feet 5 ...


61

POINT #1. lets differentiate Precision from Accuracy As it is clear from the picture we can talk about Accuracy of a measurement (e.g. GPS measurement) if we already know the actual value (exact position). Then we can say how accurate a measurement is. On the other hand if you have some measurements and don't know the actual value you can just talk about ...


35

I think this XKCD is a perfect answer to this question :) https://xkcd.com/2170/


33

I'll try to explain it in different terms: Earth's equatorial circumference is about 40,000 kilometers (25,000 miles). A latitude/longitude value breaks that distance up into 360 degrees, starting at -180 and ending at 180. This means that one degree is 40,000 km (or 25,000 miles) divided by 360: 40,000 / 360 = 111 25,000 / 360 = 69 (So, one degree is ...


31

The United States government currently claims 4 meter RMS (7.8 meter 95% Confidence Interval) horizontal accuracy for civilian (SPS) GPS. Vertical accuracy is worse. Mind you, that's the minimum. Some devices/locations reliably (95% of the time or better) can get 3 meter accuracy. For a technical document on that specification you can go here. For more ...


21

I've explored this question recently. I think people want to know what spherical radius should I use? what is the resulting error? A reasonable metric for the quality of the approximation is the maximum absolute relative error in the great-circle distance err = |s_sphere - s_ellipsoid| / s_ellipsoid with the maximum evaluated over all possible pairs of ...


17

Ionospheric delay effects are the largest source of error in a single-frequency GPS receiver. WAAS and CORS are able to correct for this better than a receiver's almanac, so the best you can do with uncorrected GPS is typically about 15 meters. Survey-grade GPS using RTK is able to achieve centimeter accuracy. Image source: http://www.spatial-ed.com/gps/gps-...


13

This illustration stuck with me, and helps me remember at the most basic level what precision vs. accuracy is.This is the source of the image, also containing a little more context. In general, Precision is the how close your grouping of measurements are. Accuracy is how close your measurement is to the actual measurement in the real world. Blah238 is right,...


11

With qualifications and suitably modified, this is correct: the standard deviation measures spread, which is inversely related to precision, while the vectors (not distances) to the reference points measure inaccuracy. Discussion With only five readings per location several problems will arise: The standard deviations of the coordinates will vary--by a ...


10

kappa does not quantifies the level of agreement between two datasets. It represents the level of agreement of two dataset corrected by chance. The reason why you have a large difference between kappa and overall accuracy is that one of the classes (class 1) accounts for the large majority of your map, and this class is well described. Overall accuracy is ...


9

As a first step, you could look at the distortions of the Mercator projection, which is a conformal projection. Distance with this projection is only correct along the equator, then the error increase with the latitude. Indeed, as you can see on a global view, the parallels keep the same legnth on the maps. For example, the horizontal scale factor, which is ...


7

Both Google Earth and Bing map use data from different sources (satellite images and ortho-photos). The horizontal accuracy depends on the source of the datasets and the level of orthorectification. It is usually better near cities than "in the middle of nowhere", but it primarily depends on the data sources. For instance, some countries have agreements with ...


7

Your understanding is correct; however, by introducing velocity and/or angular velocity and even acceleration into a model you could setup an extended Kalman filter such that at each time interval it would provide a more accurate estimate of the bearing. There are two stages to estimation in a Kalman filter. The first is the "predict" step where a state ...


6

I've had the chance to do some comparisons between iPhone data collected from a mountain bike with the data collection from a Garmin GPSMAP62sc. They were fairly close for much of the ~30km route. However, at one point they were 100m+ out. This was on a service road (so no tree cover overhead but trees to the side) and close to a river canyon and on the side ...


6

Yes. The standard methods used to cross-validate and assess Kriging also apply, practically with no change, to almost any other method of interpolation. These include jackknifing, a form of leave-out-one cross-validation in which each data point is systematically removed from the dataset and predicted using the chosen variogram model. The discrepancy ...


6

First of all, the GPS Almanac consists of information about the GPS constellation, satellites' health and their course in order to make it easier (possible) for your receiver to find them in the air. (Most of the time, you do not need to download that since you did before, but that is a discussion for another Q/A). The point is, almanac is not important for ...


6

A shapefile is capable of representing features on the ground to within a centimetre of precision. Disagreements between two spatial data sets that claim to represent the same entity may occur for several reasons. Representing a curved border with centimetre precision requires a lot of points along the border. This makes your data set very very large. In ...


5

A quick search (using no other than our great search engine god, Google) led me to this site, which further linked me to two articles. The author summarizes: D. Potere, Horizontal Positional Accuracy of Google Earth’s High-Resolution Imagery Archive, Sensors 2008, 8, 7973-7981. This paper is more than five years old and the author used control points ...


5

These are results of tests carried out in October and December 2014. Tested were the following GPS telemetry, GPS data loggers and a hand held GPS. GPSFlight STX900e telemetry, embedded GPS unit ublox LEA - S5 BRB 900 MHz GPS Telemetry, Lassen IQ series GPS receiver TLA 900 MHz GPS Telemetry, ublox 6 series GPS receiver Holux 1200e GPS data logger ...


5

I have done this when comparing collected GPS points to known positions. You want to use the distance formula Sqrt((x2 – x1)² + (y2 – y1)²). What I did was to add two new columns (X2 and Y2) to my GPS points and populate those columns with the known X and Y coordinates. In my dataset I had the X and Y coordinates of my GPS data in columns X1 and Y1. ...


5

in European countries, out in the field (not inside a city with buildings), the best accuracy without any aid is 5 meters. I have also witnessed a 2 meter accuracy but that is extremely rare and I would not take it into account. The average best would be 15 meters and the average worse close to 30-40 meters. The results stated above are from my own field ...


5

It does vary by Country - Turkey is poor because the data they used is minimal. For France, Germany, UK, Ireland the data accuracy is vastly better. If you want the accepted paper on the project "The Corine Land Cover (CLC2000) database received a thumbs up for accuracy from an assessment of the project, details of which were released by the EEA today. ...


5

I know this topic is kinda old, but I think my comment can help other fellas that have this doubt. In 2011 two brazilians published an article about it, and they concluded that: *the error is just 0,44% for line measurements; *the error is just 3,54% for polygon measurements; *the error is just 1,39% for perimeters calculation; Based on these results they ...


5

As you said, differential correction is based on the correction of the position of EACH satellite viewed in order to compute a new position. So I confirm that it is NOT possible to do differential correction if you only have the coordinates, even if you had the exact time. If you want to improve the precision of your measurements with a unit that does not ...


5

Some GPS hardware/subsystems in modern smartphones implement Kalman Filtering and sensor fusion. For example, this is the system log output (edited for relevant portions- full dump is here) from a Samsung Galaxy S3 with Android 4.3 after I fire up the LocationListener, when listening to the GPS_PROVIDER. Here you see the app (GPS Benchmark) listening for GPS ...


5

As many on this forum know, I am often for an R solution. However, in this case it is reinventing the wheel, and in a much less robust way. There is a great piece of free software, Map Comparison Kit (MCK), that implements many published and novel validation statistics for rasters. Of particular interest in this case are the Kappa, fuzzy Kappa and weighted ...


5

I would follow as below in version 9: Use sample selection algorithm(use brush and set class) and select samples and save these layer as TTA mask Then you can generate TTA mask from sample Now you can perform AC.


5

You can study the error by making SQL queries with Spatialite-gui which has a function ST_Length with a description at https://www.gaia-gis.it/gaia-sins/spatialite-sql-latest.html return the length of c (measured in meters). If the use_ellipsoid argument is set to TRUE the precise (but slower) length will be computed on the Ellipsoid, otherwise will ...


5

For the sphere you can use the SLC (Spherical Law of Cosines). The HF (Haversine Formula) will work for this as well. You can use both of these on the ellipsoid and errors are typically very low (< 0.3%). If you desire an oblate spheroid then yes use VF (Vincenty's Formula). For flat I am not sure it matters, do you mean a plane? If so then just use ...


5

Let me focus just on the question of the most accurate way to determine distances on the WGS84 ellipsoid. The accuracy of Vincenty's method is about 0.1 mm providing it converges. It fails to converge for nearly antipodal points. My library GeographicLib is accurate to about 15 nanometers and converges everywhere; the algorithm is published in my paper ...


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