Questions tagged [accuracy]

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

Filter by
Sorted by
Tagged with
0 votes
0 answers
29 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 ...
0 votes
0 answers
40 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 ...
9 votes
1 answer
121 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 ...
0 votes
0 answers
15 views

Why does an online GNSS satellite calculator give elevations ~15° different from what a GNSS app reports?

At https://satpredictor2.deere.com, satellite elevations above the horizon are given as, for example, 65° for GPS satellite 1, 38° for GPS satellite 3, etc. for my current location and time. Using the ...
  • 145
0 votes
1 answer
34 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 ...
  • 127
0 votes
0 answers
32 views

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 ...
0 votes
0 answers
77 views

Classification assessment supervised in Google Earth Engine: training samples or validation samples?

I'm using a supervised classification on the GEE and I have to evaluate my results. I came across some terms that I didn't understand their application. According to the official GEE bibliography, in ...
1 vote
0 answers
106 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 ...
0 votes
1 answer
71 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 ...
0 votes
0 answers
189 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 ...
0 votes
1 answer
36 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 ...
  • 101
0 votes
0 answers
47 views

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'...
  • 11
0 votes
1 answer
56 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 ...
1 vote
1 answer
453 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 ...
  • 11
0 votes
2 answers
562 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....
  • 3
1 vote
0 answers
154 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 ...
1 vote
0 answers
73 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 ...
2 votes
0 answers
53 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 ...
2 votes
1 answer
444 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 { &...
  • 71
0 votes
0 answers
325 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 ...
  • 101
0 votes
0 answers
30 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 ...
5 votes
2 answers
1k 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 ...
2 votes
0 answers
100 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 ...
-2 votes
1 answer
722 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 ...
2 votes
1 answer
310 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 ...
  • 23
1 vote
0 answers
86 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 ...
1 vote
1 answer
108 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 ...
0 votes
1 answer
57 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 ...
5 votes
1 answer
212 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 ...
  • 51
-1 votes
3 answers
305 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 ...
  • 1
7 votes
2 answers
298 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 ...
  • 81
0 votes
0 answers
246 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 ...
1 vote
3 answers
286 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 ...
  • 49
1 vote
0 answers
81 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 ...
  • 11
2 votes
1 answer
798 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 ...
2 votes
0 answers
160 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 ...
  • 509
1 vote
1 answer
222 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 %. ...
  • 57
1 vote
0 answers
59 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 ...
  • 61
2 votes
0 answers
57 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 ...
1 vote
0 answers
86 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 ...
  • 483
2 votes
1 answer
1k 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 ...
  • 437
2 votes
1 answer
575 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 ...
  • 437
2 votes
0 answers
59 views

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 ...
  • 69
1 vote
1 answer
164 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 ...
  • 483
1 vote
0 answers
131 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 ...
  • 11
1 vote
0 answers
56 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 ...
  • 19
0 votes
0 answers
841 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 ...
  • 101
1 vote
0 answers
144 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 ...
  • 533
1 vote
1 answer
419 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 ...
1 vote
1 answer
245 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 ...
  • 119

1
2 3 4 5