Questions tagged [accuracy]

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

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What is the maximum horizontal error allowed to call a map to be in "State Plane" coordinate system?

I work a lot with data from the drones (UAV), and some of those data are not very accurate (precise, just not accurate). For example I have an orthoimagery that is 10 feet off from its true location. ...
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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 ...
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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 ...
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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 ...
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Accuracy assessment of land class covers in ArcGIS

I want to compare the accuracy of citizen scientists in mapping a satellite image by using a raster labelled by an expert as my ground truth. How can I do this in ArcGIS Pro? What I've tried so far: I'...
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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 ...
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Field Equipment: Avenza Pro reports iPad internal GPS accuracy when paired with EOS Arrow 100 GNSS Receiver

I would like your input on an issue I'm having with Avenza Pro on an iPad mini 6, paired with an EOS Arrow 100 GNSS receiver. The Arrow pairs with the iPad and reports submeter hrms inside the Eos ...
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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 ...
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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....
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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 ...
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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 ...
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What is the accuracy of DMS coordinates that don't contain any seconds [duplicate]

For example, if I have coordinates for latitude 50°52'N, about how accurate are these coordinates? Within 10 km? 100 km? All the information I'm seeing is about decimal degrees, and I could convert ...
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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 ...
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2 votes
1 answer
216 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 { &...
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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 ...
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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 ...
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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 ...
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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 ...
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-2 votes
1 answer
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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 ...
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2 votes
1 answer
192 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 ...
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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 ...
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1 answer
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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 ...
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1 answer
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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 ...
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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 ...
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208 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 ...
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2 answers
225 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 ...
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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 ...
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3 answers
212 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 ...
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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 ...
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1 answer
445 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 ...
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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 ...
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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 %. ...
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QGIS SCP pulgin layer output

I use the plugin regularly and have already used every function. But I have often noticed that the output layers are not always intuitively understandable. I googled on the topic and found no ...
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Landsat L1GS product processing to change detection analysis ready state

At high latitude area of Svalbard Norway, one can find Landsat 8 data processed to L1TP level. With previous Landsat missions, this is not the case. Landsat 7 data are processed to L1Gt level and ...
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When creating a confusion matrix, can you have more ground-truth points than the recommended 10-times the number of classes you have?

Using ArcGIS Pro, I classified a field of grain sorghum (supervises, pixel-based support vector machine) using 5 classes: Soil, Shadows, Leaves, Heads, and Ground targets (this was a UAS study). The ...
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2 votes
1 answer
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Implementing proportional stratified random sample in R

I've completed a landcover classification on an Landsat Image and would like to start an accuracy assessment. I'd like a stratified random sample that has a sample number that varies based on each ...
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2 votes
1 answer
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How to randomly stratify sampling within landcover classes?

I'm working on an accuracy assessment of a classified landsat image and I'd like input on the best possible way to generate random points across both the classified image and a ground truth image I ...
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Combine polygons from different sources

I am currently working on a project where I try to reconstruct historical borders of the austro-hungarian empire between 1815 and 1918. Therfore I use the comination of digitized old maps an legal ...
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1 answer
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Checking accuracy of supervised classification method in ArcGIS Pro

I have a question about my image classification method in ArcGIS Pro 2.4. I'm looking at a field of grain sorghum and doing a project that requires me to define certain features within the image for ...
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QGIS wrong measurments on Google satellite images

I am new to QGIS but I understand the basic principles. I'm working with QGIS 3.8.3 on OpenSUSE Tumbleweed Linux using the KDE environment. Still trying to figure out QGIS, I'm opening a brand new ...
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Accuracy of ArcGIS Collector

About ArcGIS Collector app, what's the difference between accuracy in the setting tab and horizontal/vertical accuracy as indicated left-bottom on the map while surveying? For example, if I set the ...
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650 views

Does HDOP correlate with GPS position accuracy?

I collected 1000+ position data from GPS receivers and realized that a position with lower HDOP does not necessarily have higher accuracy. So my question is does HDOP correlate with GPS position ...
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Simultaneous raster downsampling/downscaling and upsampling/upscaling for false accuracy minimisation

I want to have a raster stack of two different resolutions. One is from VSNIR and one from SWIR sensors (hyperspectral). The VSNIR has a resolution of 25 cm and the SWIR of 80 cm and both data have ...
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1 vote
1 answer
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Sampling stratified random points using R for accuracy assessment

I want to sample stratified random points using R. I found the sampleStratified function from the R raster package. This functions samples the same amount of points for each class of my ...
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1 vote
1 answer
176 views

Options for precise relative position calculations

I'm investigating an industrial application that has a requirement to calculate with precision the relative distance on the ground between two outdoor points in the following scenario: The first ...
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Accuracy of Google Maps geo-coordinates vs high precision GPS receiver

I need to know how accurate coordinates obtained from Google Maps/Earth are. Are they 'quasi absolutely' (I know there is no absolut location determination)? In other words, if I record the ...
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1 vote
0 answers
61 views

Classification result from SAGA GIS shifted by 5 meters if used in ArcMap?

I use a band composite of 10 Sentinel-2 bands for my classifications. If I use the same composite in SAGA to make a classification this classification result is shifted by 5 meters to the left and to ...
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1 answer
167 views

GPS accuracy deviation the same in an area?

I am using a GPS receiver to perform a speedtest over a few meters. I’ve read that the GPS is accurate up to 4 meters. Is the deviation the same in an open area and also over a short period of time? ...
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1 vote
0 answers
361 views

How can I compute confusion matrix using Python [closed]

My project is about "Extracting water and urban features from satellite images". I have extracted urban and water features using Python code. Now, I want to do accuracy assessment. I know two primary ...
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2 votes
0 answers
40 views

Is there a faster way to assess accuracy of image classification in ArcGIS?

I am trying to perform accuracy assessment on a raster RGB image after supervised classification. I know the normal workflow in ArcGIS would be to create accuracy assessment points, then evaluate each ...
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