# Tagged Questions

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

388 views

### How to store Large Raster Images of Equipotential Surface Generation Using Monte Carlo Simulation?

I have a large (1GB+) raster that I am using as the base for the generation of an equipotential surface. This is to assess the accuracy of DEMs derived from another source. In situ observation is ...
816 views

### ENVI 5.2.1 How to do an Accuracy Assessment using test data from a shapefile

ENVI 5.2.1. From a .tiff image (4 bands) I created a Supervised Classification Maximum Likelihood .dat file. Now I want to perform an Accuracy Assessment using test data from a shapefile. I've tried ...
78 views

### point created on a line not precisely on line

In QGIS I wanted to move points to the nearest lines. I checked the solutions here, but there are using tools which I am not familiar to yet(POSTGIS or GRASSGIS). I figured out my own way with using ...
13 views

### How to use single frequency PPP

I read that with single frequency PPP you are able to achieve decimeter accuracy. There are services, that offer free online services to correct GNSS posistion to make it more accurate (http://www....
70 views

### Basemap (Matlibplot) not plotting GPS WGS84 coordinates accurately

I have a list of lat,lon coordinates from Flickr pictures taken in Sydney (see here) When I plot these points on google maps, the locations are correct. However when I use my Basemap the results are ...
178 views

### Benefit of DGPS for relative accuracy and speed measurements for receivers close-by each other

Consider that we are interested only in the speed and relative position accuracy of GPS receivers (i.e. their absolute try position on earth is NOT important). These receivers are all in a 90m x 90m ...
21 views

### increase resolution of gps track (roads)

I've got a group of fairly low resolution gps tracks which follow a bunch of roads. I am trying to improve increase the number of points. I tried passing through a catmull, but that resulted in large ...
142 views

### How to measure RTK accuracy of a moving vehicle?

I am currently working with tractors using a RTK enhanced automated steering system. One of the biggest problems is that even RTK can have a inaccuracy of 2cm. This can be too much for some possible ...
144 views

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

Are there any references on the accuracy or (min/max/avg) error of Web Mercator when it comes to e.g. distance calculations? For the sake of completeness, I haven't found any reference to the ...
130 views

### Using shapefiles as a reference for accuracy assessment in ecognition

I classified my project and got an esri shapefile with points in it. Those points are hand made samples with the right class assigned to them. Now I need to use those samples to check my own ...
27 views

### Accuracy assessment in Erdas imagine

Is it necessary to do an accuracy assessment for an unsupervised classification done for a Landsat 5 image?
35 views

### Working out meter accuracy based on number of visible GPS satellites?

I am working with NMEA data and I curious whether there it is possible to calculate the accuracy, in metres, based on the number of visible satellites or whether there is an alternative way? The two ...
37 views

### Matching drone point cloud data with original lidar survey? [duplicate]

I have point cloud data collected from a drone of a particular area. I too have the point cloud data collected from the lidar survey. Both are georeferenced. Now, I need to match the point cloud data ...
969 views

### How to perform an accuracy assessment in eCognition?

How to do accuracy assessment of classified images in ecognition? I have done the image segmentation for Worldview-2 image. Then, I have processed for classification for class names (e.g road,...
55 views

### How to interpret accuracy assessment results for classified data?

eCognition has the ability to perform an accuracy assessment for classified data by using an error matrix based on a TTA mask. The image shows the results of the accuracy assessment. Is there a ...
102 views

### Remote sensing accuracy assessment - McNemar`s Test

I would like to know how you determine the f12, f21 parameters for use in the McNemar`s test when for example I have two confusion matrices such as below: (where f12 = number of cells misclassified ...
36 views

### \$length calculation anomaly

A polyline layer's (green) length is being calculated via \$length. Result: ~100 meters (EPSG 31466). A buffer of 5meters is created and via Voronoi Polygons (and several other steps) a centerline is ...
24 views

### Is there a well-known way to compare the relative accuracy of 2 latitude/longitude results?

I have 2 geocoding results (in latitue and longitude) for a given address from different services. I'm interested in describing the results in relation to one another in terms of relative accuracy and ...
29 views

### Can typical Meets and Bounds (angles and distances) drawings be accurate in QGIS?

I’ve been working with parcel boundary shape files (.shp), standard satellite imagery, and Meets and Bounds (angles and distances) site maps / legal descriptions for a few weeks. Wondering if those ...
16 views

### Proper Tool for Creating a 3x3 Window for Cluster Sampling in Accuracy Assessment?

I'm using a cluster sampling scheme for an accuracy assessment of the 2011 National Land Cover Dataset (spatial res of 30m). I'm using Google Earth Pro for my reference data spatial res of 15m). So ...
46 views

### Creating a Grid For Raster When Measuring Land Cover In Accuracy Assessments

I am assessing the accuracy for the 2011 National Land Cover Map (NLCD). Each pixel for the NLCD measures 30m x 30m. For my reference data, I'm using two sources: 1) Google Earth (~20 m ...
2k views

### How is Precise Point Positioning (PPP) exactly done?

I am looking for a positioning accuracy that is higher than normal consumer-grade GNSS receiver (mostly GPS/GLONASS hybrids with +- 5m precision). I came across RTK with dual receiver setup (base ...
56 views

### Pacific-wide Projection for distance?

I have a data set of ~3500 points located across the Pacific Ocean, and am looking to measure the distance from each point to it's nearest coastline to identify the "host" country. I had originally ...
184 views

### How does a GPS device determine bearing?

Following a discussion on Math and this particular comment, I am wondering how a GPS receiver determines its bearing. As I understand it: GPS is not a directional system, thus bearing can only be ...
115 views

### Find out if overlaying polyline matches polygon centerline in qgis

I have a polygon and a polyline and I need to find a scientific way of how close that polyline is to the actual polygon centerline. Is there any way of doing this in qgis? Any extensions, models, ...
1k views

### GPS Elephant Tracking: Utilizing A-GPS, WAAS, DGPS and Understanding HDOP, NSAT, and ZDA

*I'm using a GPS data logger (qstarz bt-q1000xt) to track the movement of zoo elephants, and I have a variety of technical questions. I've had limited success receiving answers from the vendor. You ...
153 views

### Average stationary position with GPS

Is it possible to average a stationary position with a GNSS (GPS, GLONASS...) with a centimeter accuracy without external corrections (like differential or RTK)? If so, how long does such averaging ...
6k views

### How correct is the “Accuracy” value given by GPS devices?

I have a Garmin Forerunner 305 and a Google Nexus One Android phone. From the GPS on both these devices I can get a "Accuracy" value that is usually between 6-20 meters. How much can I trust this ...
437 views

### Accuracy of GPS and HDOP

Given a handheld GPS with an accuracy of roughly 2 meters (verified through field tests) and an observation with an HDOP of 1.2, the accuracy of that one observation should be within 2 meters X 1.2 of ...
101 views

### What view of sky is required for RTK GPS

When using RTK or differential GPS technologies, considering the Base has a clear unobstructed view, what view of the sky is required to be able to get an accurate fix with the rover when is moving (...
3k views

### What class/types of smartphone chipsets support GPS, A-GPS, GLONASS AND have extended kalman filtering?

I've been testing several Android phones (all running Android 4+) Sony Xperia T, Moto G, Nexus and HTC 1 which are all giving decent tracks (all of which use GPS/GLONASS) However we are also using ...
41k views

### What is the maximum Theoretical accuracy of GPS?

I was talking with a potential client, and they requested that we plot some points with GPS, with a maximum (or should that be minimum?) accuracy of 2 m. This is an area with no WAAS, and I was under ...
9k views

### Low-cost centimeter-level accurate satellite positioning (GNSS/GPS) [closed]

I am looking for a low-cost (< US\$500) GNSS/GPS setup with a centimeter precision without much HW hacking. I am not able to produce my PCB or do any soldering (though I would do that if there is no ...
53 views

### Accuracy calculated by GPS

I found a lot of pieces of an answer to this question, but no complete and good one. How does a GPS System calculate it's own accuracy at the moment? Where does it get the known position to ...
85 views

### Collector blue accuracy ring- what does it show?

What, definitively, does the blue accuracy ring show in Collector. In the field it always seems too large to represent the accuracy that the GNSS app is stating (ie 50cm – 1m). The blue ring seems to ...
112 views

### Elevation adjustment DSM using Ground control points

is there any possibility to improve the vertical accuracy of a given satelite DEM/DSM by using exact measured ground control points? And if so, which software is recommended?
1k views

Does anybody know the accuracy of Google Earth, Google satellite, and Bing aerials, and at what scale? I think that you have different/better accuracy if you have subscribed to their professional ...
492 views

### How to compare two sets of points in QGIS?

I have two point layers with XYZ data; one set are points measured in the field and the second set is a Lidar data set. I want to check the accuracy of the Lidar in comparison to the measured data. ...
66 views

### Checking the registration accuracy of already-orthorectified images

I acquired several Landsat 5-8 images corrected at Level 1T. I also have aerial ortophotos of the same area. From a visual assessment the co-registration between the images seems good, but I need to ...
114 views

### Is this distribution of GPS positions caused by multipath distortion?

I have some GPS points that are close to where they should be, but not nearly close enough (horizontal precision is around 10 meters). Looking at the positions which comprise these points (there are ...
5k views

### How accurate is approximating the Earth as a sphere?

What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them. Are ...
201 views

### Measurement of accuracy for image segmentation of land cover image in python

I have a land cover image and I segmented it using K-means clustering algorithm. Now I want to calculate the accuracy of my segmentation. How do I do that? I have read about dice similarity co-...
84 views

### Geocoding Adresses with varying levels of reporting accuracy?

I am trying to geocode a database that has, I'll call it "4 tiers", of address types. They are: Numbered Street (e.g. 506 Taproom Way) Cross-street (Happy Road \$ Jubilant Blvd) Hundreds Block (500 ...
155k views

### How to measure the accuracy of latitude and longitude?

I am very new to GPS stuff. Suppose I have latitude and longitude as 19.0649070739746 and 73.1308670043945 respectively. In this case both coordinates are 13 decimal places long, but sometimes I also ...
642 views

### How to calculate RMSE of geographic coordinates?

I've been working on my project and I stumble upon how I can calculate the Root Mean Square Error (RMSE) of geographic coordinates. What I have is a derived coordinates from processing LiDAR data ...
427 views

### Relationship between contour interval and spatial resolution of a generated DEM

If I have contour lines with interval say 10, 5, or 2 (etc.), and I generated a DEM from them, what is the relationship between between the contour interval and the resolution of the DEM? Irrespective ...
46 views

### Transfer from Android phone to Windows OS truncates lat long

I am clicking GPS enabled pictures of sites which are less than 500 metres apart through Android based Samsung ACE Duos phone. I later use Google Earth on my Laptop to view these geo tagged pictures. ...
5k views

### Is GPS more accurate on specific hours of the day?

I have heard that the GPS system is more accurate, and less accurate on some specific hours on the day. If this is true, how can I get the information on when GPS is more or less accurate at my ...