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Questions tagged [accuracy]

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

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Edit feature without losing GPS data in QField

I use QField to collect data entered manually in the field. But also internal GNSS data (horizontal and vertical precision). In the QGIS form I save the default values: @gnss_horizontal_accuracy and @...
Nicolas's user avatar
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30 views

OpenStreetMap Polygon data accuracy checking

I was wondering whether there is a method or exercise I can do to check the accuracy of building polygons sourced from OpenStreetMap (https://download.geofabrik.de/)? Of course when I layer the ...
Izzy's user avatar
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2 answers
75 views

Converting vectorization (raster to vector) with small steps in values in QGIS

I have a raster file that contains water depths in m. The water depths are the only attribute and should be transferred to the vector layer. The raster files have a cell accuracy of 1m x 1m. I would ...
Pia Rösel's user avatar
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Why if I spoof the position with GNSS Analysis MATLAB Google code,I get a spike of horizontal speed but it continue to be active while should be const

I'm using this GNSS Analysis Matlab Google code to analyze the measurements performed via GNSSLogger app. I was initially in Palermo,Sicily and tried to spoof to Rome. I get this Horizontal speed ...
allexj's user avatar
  • 11
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1 answer
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Finding accuracy of water indices

I have calculated the water indices NDWI, MNDWI, WRI, and applied binary thresholding. I want to find out the accuracy of these indices.
shriram kathar's user avatar
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1 answer
134 views

File not found, no such file or directory in GEE python

I follow step by step in : https://geemap.org/notebooks/33_accuracy_assessment/#split-training-and-testing When the step to download confusion matrix, there is error. I type the code : import csv ...
mega saputra's user avatar
3 votes
1 answer
146 views

Buffer accuracy in virtual layer differs from accuracy in PostGIS view

I used virtual layer query to create a buffer for a point as this allowed me to transform its SRID using the PostGIS function ST_Transform, which is not possible with the ready-to-use Buffer algorithm ...
Michele Cordini's user avatar
3 votes
0 answers
131 views

Accuracy assessment of unsupervised clustering - GEE

I have clustered my map on the basis of NDVI values using an unsupervised approach. I don't have the labels. However, I do have the cluster IDs that were automatically assigned. How do I assess the ...
th145's user avatar
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1 answer
4k views

Android GPS accuracy (2 m) is greater than nominal accuracy

I read in several posts and websites that public GPS signal to smartphones has an accuracy of around 5 m, and that civilian signal accuracy is 100 m. Some other posts mentioned accuracy of c. 2 m and ...
rodrikev's user avatar
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370 views

How to calculate accuracy of a calculated (predicted) coordinate (latitude, longitude)?

Given GPS data that consists of: Latitude Longitude Bearing (degrees) Speed (meters per second) Accuracy (radius of the circle around the coordinate where true position can be found with 68% chance, ...
Chaz Ashley's user avatar
1 vote
1 answer
108 views

Calculating distance discrepancy: EPSG 3112 Projection VS GeoDesic (Karney), is ~0.5% difference normal?

I have lat-lng coords in EPSG:4326, and I'm calculating the distance between them (in metres). Since these are in Australia (and Australia wide, therefore no specific MGA zone projections), I'm using ...
Melbourne Boi's user avatar
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138 views

Accuracy Assessment of NDWI - GEE

I have applied NDWI (Normalized Difference Water Index) on years: 2018, 2019 and 2020 to extract the water bodies. Then I used MCD12Q1.061 MODIS Land Cover Type Yearly Global 500m product for the year ...
th145's user avatar
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1 answer
72 views

Low accuracy for addition of more predictor bands in Random forest classifier

Hi there Im working on a project for estimation Above ground Biomass in hilly terrain for mature forests and asscessing accuracy of different classifiers availiable in GEE such as Random forest and ...
asim qadeer's user avatar
1 vote
0 answers
39 views

Accuracy assessment on multiple classified images

I am attempting to compare the accuracy of multiple different classified images I have created from a single raster. Basically, I want to avoid having to input 'ground truth' values for each accuracy ...
Matt Dupasquier's user avatar
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1 answer
111 views

Classification map in GEE does not correspond to accuracy results

I have this script in GEE that has worked successfully before for LULC mapping (with 8 classes). I used this script for mapping solar panels (2 classes: solar & non solar). The accuracy results ...
Paris's user avatar
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1 answer
706 views

How to find the standard deviation in GPS measurement of latitude and longitude?

Let's say my GPS configuration is said to have a precision of 10 meters. I have taken this as the standard deviation in the GPS measurements. But the measurements that come from GPS are latitude, ...
rohit kumar singh's user avatar
1 vote
2 answers
125 views

Tell GeoPandas the number of significant figures to use when writing GeoJSON geometries

I have a GeoDataFrame gdf. I write its contents to a GeoJSON: gdf.to_file("example.geojson") which works. However, each geometry is specified to 16 significant figures, which is an overkill ...
zabop's user avatar
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233 views

Increasing accuracy with RF classifier in GEE

I am doing a supervised classification using RF classifier in GEE. However, the accuracy that I am getting is not exceeding 0.67, even if I increase the training sample or no. of trees in my ...
Samar Tarek's user avatar
9 votes
1 answer
307 views

Why recommended transformation is not the most accurate in QGIS?

When I am prompted for a transformation to use in QGIS, the recommended/default option (in green) is the least accurate one. In my case, QGIS recommends a transformation with an accuracy of 6m when ...
Immersion.Ninja's user avatar
0 votes
1 answer
35 views

HUGE latitude error from iPhone 4s

2015 April 15, I wandered around Little Rock, Arkansas, on bike, taking pictures with an iPhone 4s. Cloudy day, though some photos show shadows. Here are some of the metadata from three consecutive ...
WGroleau's user avatar
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How can I calculate the midpoint between three points using accurate variables like Horizontal accuracy and HDOP

I have three (3) points with the following fields: X Y Horizontal Accuracy Vertical Accuracy PDOP HDOP VDOP And I would like to calculate the midpoint between these three points, using accurate ...
Jhon Galindo's user avatar
1 vote
0 answers
185 views

How to compute theoretical GPS accuracy?

I'm a student and I am working on a GPS-like system. I have implemented a few algorithms (Newton-Raphson, Bancroft, ...) and I would like to compare them. Basically, I have a constellation of ...
ALEIXANDRE's user avatar
0 votes
1 answer
316 views

How can I improve the accuracy of a DEM using surveyed points?

I have a DEM and many surveyed points in the area. The survey points have centimeter accuracy. The difference between the DEM to the actual height ranges from -20cm to +20cm. It is not a uniform ...
K.Frantzios's user avatar
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337 views

OpenLayers vector accuracy in EPSG:3857 projection

I'm working on a web mapping solution that stores data in PostGIS with EPSG:4326 projection. Everything seems to be good until last week. My customer loaded two shapefiles that some parts are ...
Alper Dincer's user avatar
0 votes
1 answer
63 views

Set marker size equal to GPS accuracy with variable opacity?

I have an exported collection of iNaturalist observations which have latitude and longitude values, but also report the GPS accuracy in meters. This data is in the form of a csv file. The accuracy ...
Galen's user avatar
  • 103
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1 answer
86 views

Sudden change in altitude during measurement with GNSS

We work For some time now we have been working with QField and the GNSS receiver from Emlid. We get the accuracy via bluethoot from the receiver to QField. Lately, however, the measurements have been ...
Céline's user avatar
1 vote
1 answer
842 views

Evaluating classification accuracy and the result of kappa test in Google Earth Engine

I am trying to check the efficiency of the classification. The classification accuracy and kappa test for 2020 are 0 while for 2000 is 1. I am just not able to put my finger on what is incorrect as ...
ANat's user avatar
  • 11
0 votes
2 answers
1k views

Can I get ~1cm accuracy with a 2.5m accuracy GPS module and RTCM/NTRIP data after post processing?

I'm a new on this, so I have a subscription to a RTK? service that sends correction data (RTCM/NTRIP) over GPRS/UMTS (you get a SIM card with the subscription) I'm also having a Rover of around 2mx1....
Ricker's user avatar
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1 vote
0 answers
333 views

What does the coordinate values represent when using WGS 84 / Pseudo-Mercator (EPSG:3857)?

I have been using QGIS for a couple of weeks now, mostly for data collection in my research project. Currently, I'm trying to plot these points, in a graph similar to this one (but in kilometers), I ...
mbk_wass's user avatar
1 vote
0 answers
128 views

How to calculate 2 sigma circular approximation for GNSS positional accuracy?

I'm using gpsd application and I get the positional accuracy related data, i.e., semi-major axis accuracy semi-minor axis accuracy and semi-major axis orientation of the error ellipse. These values ...
RAMANA REDDY's user avatar
2 votes
0 answers
62 views

Under which condition(s) does geopositioning precision infer accuracy?

I am not sure whether this is the right forum for this question but I reckon that since it gathers experts in GIS, the odds of someone having valuable insights is higher than anywhere else. So here's ...
Serge de Gosson de Varennes's user avatar
2 votes
1 answer
1k views

How to interpret gpsd TPV accuracy info

I want to understand the epx (Longitude error estimate in meters, 95% confidence) and epy (Latitude error estimate in meters, 95% confidence) values in a gpsd TPV packet. If I have data like this { &...
ddd's user avatar
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0 answers
652 views

Accuracy of Google maps/HERE maps

According to this article in https://junipersys.com/support/article/6614, I have a basic understanding of the accuracy of GPS data. Through calling Google Maps/HERE Maps API, we are able to receive ...
Fly_back's user avatar
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0 answers
38 views

Controling accuracy of polygon data using ArcMap

I have a question regarding polygon data. I implemented "Calculate geometry" and the new column includes the area of interest to ha. The problem is with the accuracy of the data. The site ...
StavGian's user avatar
7 votes
3 answers
3k views

Is it possible to achieve sub-meter accuracies with a smartphone, without using an external GNSS-receiver?

I am currently working with QField on my tablet (Samsung Galaxy Tab S5e) and my smartphone (Samsung Galaxy A40). Since the positioning accuracy on my devices is rather low (absolute best case ~3m on ...
nuenueke's user avatar
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2 votes
0 answers
124 views

Single numbers for accuracy and resolution for vector and raster data?

This question is meant as a modelling question, not having to do with particular data formats. It was edited to better separate spatial accuracy and resolution (precision). In order to make the ...
user1867448's user avatar
-2 votes
1 answer
2k views

Accuracy of latitude and longitude based on decimal places [closed]

After reviewing various information regarding accuracy of latitude and longitude for specific decimal places, I have a question regarding the information that many have posted, such as in Measuring ...
Colby Burns's user avatar
2 votes
1 answer
524 views

Save GNSS accuracy for each vertex of polygon/line feature in QField

In QField it is possible to save positioning information in point features through expression variables like @position_horizontal_accuracy or @position_number_of_used_satellites. The explanation is ...
rob1's user avatar
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1 vote
0 answers
182 views

How to calculate the accuracy of georeferenced aerial images in meters if the mean error is in pixels?

I have scanned aerial images taken shortly after WWII and have to georeference them and calculate the mean error. I use the Projective transformation so the error after transformation is shown in ...
Pepe Pesh's user avatar
1 vote
1 answer
139 views

How to improve the horizontal and absolute accuracy of UAV layer

I am working with two digital elevation model data sets: LiDar and UAV DEMs. Both flights were conducted in the same location along a coastal shoreline showing the intertidal area with lots of bare ...
Rebecca Dodge's user avatar
0 votes
1 answer
76 views

QGIS 3.14.15: is there a build in option for storing additonal quality data from trackpoints captured with DGPS antenna

I'd like to use QGIS for collecting datapoints in field. Due to the 'GPS information module' it is no big deal to connect the R2-Antenna via Blutooth-link and read the NMEA stream. As far as I figured ...
MathiasF's user avatar
7 votes
1 answer
305 views

Loss of vector line accuracy when exporting from QGIS

I'm new to QGIS and having a little trouble understanding why my vector lines in QGIS look sharp and accurate but when I export and then import into MapBox, the line accuracy is reduced. Vector end ...
Ryan's user avatar
  • 71
-1 votes
3 answers
565 views

Accuracy of country shapefiles

I am working with a country shapefile for Pakistan, however it does not seem to be completely accurate. I wonder if this is an inherent limitation of shapefiles, or whether I could find an accurate ...
dmswjd's user avatar
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7 votes
2 answers
404 views

GPS glitch causes 200 m circles around stationary position- Has anyone seen this before?

I am working with GPS data from public transport buses in a city in the UK. The data have very characteristic circles of approx. 200 m diameter at bus stops. I suspect that these are caused by an ...
Thilo's user avatar
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0 votes
0 answers
312 views

How to redesign confusion matrices from Ecognition with python and seaborn?

I am using eCognition manual classification as a baseline for performance comparison with other 3D classification methods. For each method, I am creating confusion matrices in python with sklearn and ...
JesEcog's user avatar
1 vote
3 answers
428 views

Finding applied transformation method and accuracy information when reprojecting layer in QGIS

When I load two layers with different CRS I'm prompted to choose a transformation method and there is a column indicating the accuracy (see image 1). I would like to know where the information as part ...
Aron's user avatar
  • 59
1 vote
0 answers
165 views

Calculation GPS Accuracy based on known point

I have 3 GPS's that were on the same point for about an hour. Each of them yield a fairly accurate position but not a complete accurate location (obviously) I want to know how to calculate the best ...
DeJoker's user avatar
  • 11
2 votes
1 answer
1k views

Better GPS accuracy in Android application

We are looking for ways to read higher GPS accuracy (less than 1 m) in our Android application. We have tried with couple of mobiles having L1 frequency and supports GPS , GLONASS, Galileo etc but ...
user684805's user avatar
2 votes
0 answers
233 views

What is the best way to calculate the accuracy of GPS point measurements in relation to the road network?

I have a vector dataset containing GPS locations/points of different vehicles and a (polygon) road network dataset. Due to the inaccuracy of the GPS receiver, these gps points can deviate up to 10-20 ...
winecity's user avatar
  • 539
1 vote
1 answer
344 views

How to exclude/eliminate invalid areas (such as NoData, cloud, water, etc) from raster so that it does not effect the accuracy assessment?

I have two classified raster (snow cover % 10-100) one is prepared from coarse resolution and another is from finer resolution. I am doing accuracy assessment and matrix calculation of snow cover %. ...
Tua's user avatar
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