87 votes

Measuring accuracy of latitude and longitude

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 ...
Hossein Narimani Rad's user avatar
65 votes

Measuring accuracy of latitude and longitude

I think this XKCD is a perfect answer to this question :) https://xkcd.com/2170/
Yuri Astrakhan's user avatar
12 votes
Accepted

What's the accuracy of Web Mercator EPSG:3857?

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 ...
radouxju's user avatar
  • 49.6k
11 votes

Measuring accuracy of latitude and longitude

The other excellent answers here are primarily about latitude. A degree of longitude shrinks from about 111 km at the equator to 0 at the poles, so the nominal precision of a decimal degree of ...
John's user avatar
  • 518
8 votes

What's the accuracy of Web Mercator EPSG:3857?

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 ...
user30184's user avatar
  • 64.6k
8 votes
Accepted

Why recommended transformation is not the most accurate in QGIS?

How is this default picked by QGIS? QGIS makes a query to PROJ libraries to obtain the list of possible transformations between two reference frames or geodetic datums. Sorting algorithm is ...
Gabriel De Luca's user avatar
7 votes

How correct is the "Accuracy" value given by GPS devices?

I'm surprised nobody mentioned CEP - Circular error probable. Actually the accuracy in meters provided by your GPS means that it's accurate within X meters from actual position 50% of the time! https:...
Daniel Lengyel's user avatar
7 votes

How does a GPS device determine bearing?

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 ...
somerandomdude's user avatar
7 votes

Which is the most accurate method of measuring distance?

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 ...
cffk's user avatar
  • 3,241
6 votes

Which is the most accurate method of measuring distance?

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 (< ...
If you do not know- just GIS's user avatar
6 votes

Accuracy of country shapefiles

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 ...
Spacedman's user avatar
  • 63.2k
6 votes
Accepted

Buffer accuracy in virtual layer differs from accuracy in PostGIS view

When using a virtual layer, even over a postgres layer, you are not using postgis functions but rather spatialite functions. We can see that st_buffer, in spatialite, has a default of 30 segments per ...
JGH's user avatar
  • 41.6k
5 votes

Accuracy of measurements in Google Earth

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,...
Rodrigo Sartori Bogo's user avatar
5 votes

Accuracy assessment in R?

Post a reproducible example for a better solution of your problem. I will use a personal example to show you: Reference Prediction FPers FCadu Prade SinVg FPers 9....
aldo_tapia's user avatar
  • 13.4k
5 votes

How to check accuracy of Roads

Rather relying on online service, you should download a high resolution imagery, geo-reference it accurately and then use as reference for quality assurance. See the resources for fundamentals of ...
Junaid Abdul Jabbar's user avatar
5 votes

Accuracy assessment using Google Earth Engine?

Yes, you can. This page describes how to do it. // Make a Random Forest classifier and train it. var classifier = ee.Classifier.randomForest(10) .train({ features: training, ...
Nicholas Clinton's user avatar
5 votes

Loss of vector line accuracy when exporting from QGIS

First off: Mapbox GL accepts EPSG:4326 - WGS84 referenced coordinates only, and transforms to either EPSG:3857 - Spherical (Web) Mercator directly, or into Vector Tile space. Then: Mapbox GL ...
t.ry's user avatar
  • 81
4 votes
Accepted

Find out if overlaying polyline matches polygon centerline in qgis

Taking into account your trouble with vector solution I suggest using approximate raster based technique. I’ll use ArcGIS (no QGIS) but most likely there are same tools in QGIS Dissolve your polygons ...
FelixIP's user avatar
  • 22.8k
4 votes

Using shapefiles as a reference for accuracy assessment in ecognition

To calculate overall accuracy assessment in eCognition using shapefiles you need to do following steps: First, add shapefiles in to eCognition as thematic layer by modifying the project. (make sure ...
Gulnur Khalmurzayeva's user avatar
4 votes

Pacific-wide Projection for distance?

It depends on your accuracy needs. Fortunately, since you only have to make a discrete decision--which country is closest?--you only need reasonably good relative accuracy in the directions towards ...
whuber's user avatar
  • 69.7k
4 votes

Remote sensing accuracy assessment - McNemar`s Test

McNemar's test is a test for paired proportions, I do not see how it applies to a multi-class confusion matrix. Commonly, it is applied to validate logistic models. You cannot hope to aggregate the ...
Jeffrey Evans's user avatar
4 votes

Apply accuracy measures from partial area to the whole classified maps?

If your area of overlap is large enough and the land cover in the scene is homogeneous, you can make the hypothesis that your area is representative. Under that hypothesis, you can use a stratified ...
radouxju's user avatar
  • 49.6k
4 votes

How to check accuracy of Roads

Satellite data is always shifted. The reason is that accuracy of raster data for large area is not so high (1m, sometimes even 10m) and it will always generate errors. I would suggest to use some ...
Losbaltica's user avatar
  • 1,469
4 votes
Accepted

What is the meaning of Altitude in EXIF of an image?

The newest EXIF specification http://www.cipa.jp/std/documents/e/DC-008-Translation-2016-E.pdf knows only GPSAltitudeRe and GPSAltitude. They are defined as GPSAltitudeRef Indicates the altitude ...
user30184's user avatar
  • 64.6k
4 votes

Heuristic relationship between number of satellites and GPS precision?

Regarding Position Errors The ATS Wildlink 500 ("ATSW500") outputs what is known as autonomous positions. The errors of autonomous positions are normally distributed if and only if (1) the device (...
Ralph Tee's user avatar
  • 1,702
4 votes

How to create circles around points

If you project your dataset from WGS84 to a projection with meters as the unit of measure you should be fine with doing the steps you've described above. To do this, right click on the layer in the ...
pdavis's user avatar
  • 827
4 votes
Accepted

How to randomly stratify sampling within landcover classes?

It s best to avoid converting to vector to do the sampling if you do not have to. You can use the sampleStratified() function in the raster package to generate randomly stratified points in your land ...
Aaron's user avatar
  • 51.6k
4 votes

Accuracy of latitude and longitude based on decimal places

There is 100 cm in a meter, not 1,000 and only 10mm in a cm, not 1,000. So you are 1,000 times out in your calculation.
Leigh Bettenay's user avatar
3 votes

Accuracy Assesment in R

There is a confusionMatrix() function implemented in R: library(caret) #required for confusionMatrix() #example values a <- c(1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1) #values from classification b <- ...
Iris's user avatar
  • 894
3 votes

How to interpret accuracy assessment results for classified data?

I recommend reading Russell Congalton's book Assessing the Accuracy of Remotely Sensed Data: Principles and Practices for a comprehensive analysis of the subject. Looking at your accuracy assessment,...
Aaron's user avatar
  • 51.6k

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