Questions tagged [accuracy]

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

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49 views

GPS location accuracy issue in mobile apps [closed]

I am developing an mobile app [as part of project] which computes live location (using phone GPS) every 10 seconds using flutter and native Android location libraries and calculates distance of our ...
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1answer
93 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 ...
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44 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 ...
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71 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 ...
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1answer
90 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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18 views

How to get the georeferencing mean error?

I'm georeferencing pictures and want to see the error. When using the affine transformation the mean error is displayed in meters in the bottom right corner of the georeferencing window. For the ...
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20 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 ...
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1answer
43 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 ...
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1answer
22 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 ...
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45 views

Accuracy assessment (confusion matrix) of image classification from Landsat imagery in SAGA GIS

I have classified Landsat images in two different classes, namely pervious and impervious, in SAGA GIS, using training sample in polygon shapes. This training sample has only one column of attribute ...
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1answer
105 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 ...
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48 views

Accuracy assessment of RFclassificatiton in dzetsaka plugin QGIS

I tried random forest classification on dzetsaka plugin in QGIS to discriminate different plant species using sentinell(10m) and planet(3m) image. Classification is performed but i am confused about ...
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98 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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177 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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67 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 ...
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107 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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28 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 ...
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1answer
170 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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56 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 ...
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1answer
80 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 %. ...
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37 views

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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40 views

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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61 views

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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1answer
680 views

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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1answer
177 views

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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1answer
110 views

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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69 views

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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37 views

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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498 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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96 views

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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1answer
193 views

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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1answer
128 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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2k views

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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59 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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1answer
104 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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251 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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34 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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17 views

Compare two forest loss classifications and fill missing years: accuracy assesment or correlation?

I have a time series of forest loss rasters originating from two different classifications with some missing yearly data. Rasters represents forest loss (1) or no disturbance (0) in specific year. I ...
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90 views

Computing GPS points accuracy

I have stand alone GPS points and RTK points collected at the same time and I want to compute the accuracy (1 sigma) of the GPS points. Using the haversine formula, I computed the distance between the ...
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1answer
129 views

Mapbox Vector Tiles appear to lack accurate intersection nodes?

Mapbox Vector Tiles appear to lack accurate intersection nodes. Is this a bug? i.e. should the tile's geojson include a shared node between two intersecting streets? Details: Using MVT's from http:...
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33 views

Statistic validation for spectral trajectories/trend from ground truth dataset

I'm doing an extraction of spectral trajectories for disturbed forest pixels using multitemporal (single scene for 20 years) Landsat Surface Reflectance products. Usually, forest disturbances are ...
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1answer
284 views

How to create circles around points

I'm new to QGIS so please bear with me. I'm using QGIS 3.6. So I imported a CSV-file with latitude longitude coordinates (WGS 84), created markers and set them to have different colors (to show ...
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1answer
187 views

Customized Albers Equal Area Conic projections are cosmetic only or do they affect area calculations too?

I will be doing area calculations for 100+ countries using country polygons taken from GADM, a database of global administrative areas. I am using ArcGIS. The GADM data is in WGS84 and is unprojected. ...
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54 views

Is the accuracy or PDOP included in smartphone or GPS camera?

I would like to properly geolocate picture Exifs on a smartphone or GPS camera and would like to record the accuracy of the GPS position as well. I have downloaded a few photos from camera review ...
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189 views

QField Coordinate Reference System

Does anyone know how location services on your mobile device compare to a chosen coordinate system set in the QGIS project? I am wondering how to improve the accuracy of my device compared to the ...
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1answer
4k views

How precise is GPS?

Most search results I get on this talk about the accuracy, that is how close the locations outputted by the GPS are to the real positions, of GPS. However, I'm working on a project that only requires ...
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2answers
143 views

Heuristic relationship between number of satellites and GPS precision?

I'm a statistician conducting an analysis on animal movement based on data collected using ATS Wildlink 500 collars. As part of this analysis, I'm estimating GPS error assuming that the error in the ...
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1answer
1k views

Why ground model from point cloud in Global Mapper is inaccurate?

I have a LAS file that I assumed was based on LiDAR, but it is actually based on ADS (airborne digital sensor) imagery, according to the body that captured the data. I load the file in to Global ...
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1answer
129 views

GNSS accuracy, what is it?

Using a Trimble GeoExplorer 6000 Series GeoXT Handheld, I recorded uncorrected GNSS positions, for example: Horizontal estimated accuracy in the field 4 meters. Vertical estimated accuracy in the ...