Questions tagged [sampling]

Measuring data values at specific, discrete locations.

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50
votes
5answers
13k views

What are the benefits of hexagonal sampling polygons?

I am always on the lookout for useful methods to sample or partition study areas (usually in the form of raster datasets) into smaller units. Recently, I read an ESRI blog post about a new tool for ...
23
votes
2answers
8k views

How much sense does it make to average (lat,lon) samples in order to increase 2D accuracy of a GPS location?

Several GPS applications, like this one, or this one, acquire multiple (lat,lon) samples of a given location, assuming that the GPS unit is not moving, and then take an average of the samples in order ...
19
votes
2answers
10k views

Minimum number of samples for kriging interpolation

I get some data with number of specimens with a request to interpolate it using kriging method. After some investigation it appeared that kriging results (performed in ArcGIS Geostatistical Analyst ...
8
votes
3answers
5k views

Using sampleRandom() from large raster without NA values in R?

I have a number of vary large rasters which need to be randomly sampled with the return value being a matrix of x, y, and value. The raster package sampleRandom(raster,n, na.rm=TRUE, xy=TRUE) will do ...
8
votes
1answer
192 views

Estimation of values for unsampled points

I want to measure biomass on a coastal mudflat. I can only access points inside the polygon. Are there any methods available that would allow me to estimate values of the points outside of the polygon,...
7
votes
3answers
10k views

Extract Overlapping Polygon Data to Points

I have a polygon data set of corn yield collected by a combine. However, as the combine drove through the field, there was slight overlap between passes, leading to overlapping polygons within the ...
7
votes
1answer
4k views

What sampling tools are available in QGIS?

I'm looking for a tool to generate a stratified random set of points within the boundaries of a polygon layer. In ftools 0.6.1 there is a tool which almost does what I need, but misses the stratified ...
6
votes
3answers
2k views

Randomly sample from geopandas DataFrame in Python

I am reading a shapefile as geopandas DataFrame and them using pandas subset method to select a region. geodata = gpd.read_file(bayshp) geodata.dtypes geodata.head(10) OBJECTID FIPSSTCO ...
5
votes
1answer
577 views

Plugin not available : point sampling tool

I installed the QGIS Standalone Installer Version 2.14 (64bit). I created a map in the program called QGIS Desktop 2.14.3 with GRASS 7.0.4. I need one tool from Plugin : Point sampling tool. The ...
5
votes
1answer
5k views

Is there a source for free CSV files with geo data and other desired fields? [closed]

I'm writing some software components that process geospatial data. The input data is a CSV with general columns (e.g. name) and geo columns (e.g. city, lat or zip). I would like to test these ...
4
votes
1answer
158 views

Risk of generating sampling points from Pseudo-Mercator projection

Is there any risk in using the Pseudo Mercator projection (EPSG:3857) to generate lat/long coordinates for locating sampling plots with a handheld GPS? My understanding is that since it uses WGS-84 ...
4
votes
1answer
2k views

Generate random points within a polygon with minimum distances in QGIS 2.14

I have a polygon in QGIS 2.14 and want to generate a specified number of coordinate points within that polygon, with a minimum distance apart. The fTools Random Points tool doesn't give this option, ...
4
votes
2answers
2k views

Zonal Statistics for multiple rasters

I'm trying to create a timeseries of raster data (one layer per year) by polygon (Administrative regions). Is there any way in QGIS to perform Zonal Statistics for multiple years (without having to ...
4
votes
1answer
787 views

What's the difference between sample, sampleRegions, and stratifiedSample in Google Earth Engine?

According to the documentation of GEE, ee.Image.sample() samples the pixels of an image and returns them as a FeatureCollection, in which each feature has 1 property per band in the input image. You ...
4
votes
1answer
168 views

Spatial sampling design

I have some plots of land spread across the landscape. Sometimes a parcel is subdivided in different sectors. For each parcel (and, in case of subdivision, for each sub-section) the quality of ...
4
votes
1answer
756 views

Sampling raster by line in QGIS

I am quite new to GIS, and was wondering if you might be able to help me out? I have a raster layer for gradient as well as a line created from GPS tracking points(using the point connector tool). Is ...
3
votes
3answers
233 views

Point attribute from underlying raster data TIFFTAG

I have a layer of manually set points in qgis that have the following attributes at the moment : id, lat, long Additionally, I have a number of different overlapping raster images (sattelite data) ...
3
votes
1answer
1k views

How to create one random point per grid cell? (i.e., systematic sampling with randomly placed points)

Using ArcMap, I have used the Fishnet tool to create a grid of 1km squares. I am looking to create random points so that there is one (randomly placed) point per grid cell, with a minimum distance of ...
3
votes
1answer
263 views

Stratified sampling with a point and polygon layer

I need to perform a stratified sample in the following context. I have two layers; the first is a point layer (which consists of dwelling centroids.) The second is a vector layer of polygons with ...
3
votes
1answer
164 views

Field sampling design: stratified random or transect?

I am trying to understand the impact of scientific activity in a remote polar environment. I have five locations in different parts of the region, where historic huts were placed for a couple of ...
3
votes
1answer
2k views

Extract multi values to point error

I am trying to extract values from my rasters (slope, aspect, landcover etc.) for my animal group locations. I used Spatial Analyst > Extract Multi-values to Points, but when I look in my attribute ...
3
votes
2answers
986 views

Creating Random Points that respect minimal distance across features / strata using ArcGIS for Desktop?

I have a shapefile with multiple polygons in which I want to distribute random points. Each polygon should contain exactly one point. The minimal distance between the random points should be 200m. ...
3
votes
1answer
2k views

How to generate random points with minimum distances between points in multiple polygons

I am looking to create random points for a random stratified survey. There are three different categories being surveyed; for each, I have a single shapefile, each containing a number of polygons. I ...
3
votes
1answer
885 views

Extract pixel value for corresponding gps location in R

I have animal gps data with several locations for each day and regular gaps of several days when no location of the animal was recorded. Additionally, I have satellite data in intervals of 16 days. I ...
3
votes
0answers
45 views

How does Empirical Bayesian Kriging handle sampling bias?

In ArcGIS Pro, simple kriging approaches allow you to de-cluster your data before applying a normal-score transformation. According to the Esri guideline, normal-score transformations are only ...
3
votes
0answers
144 views

Creating equidistant sampling points in polygon in QGIS 3.6.0?

I have figured out how to add random points inside polygon boundaries. Although this works well, nevertheless I need a few different things to happen for my application. What I would like to do is ...
3
votes
0answers
576 views

Getting coordinates of pixels [closed]

I want to compute an area of certain object on a picture using Monte Carlo method. The picture shows some shape on white background. To do so I figured out that I'd get the coordinates of non-white ...
2
votes
3answers
3k views

random sampling from spatial points in R

Can anyone help me out on the best package to sample from a spatial point dataset? My dataset consists of a list of positions inside a region, and for each point I also have the name/number of the ...
2
votes
1answer
394 views

Understanding spsample in R?

I have read the documentation for this but still unsure of what the function spsample does. The documentation is here: https://www.rdocumentation.org/packages/sp/versions/1.3-1/topics/spsample I ...
2
votes
2answers
346 views

Point Sampling Tool pyQGIS

I have several raster files (raster_1, raster_2, [...], raster_n) and a point shapefile. The point shapefile (point.shp) was created using "generatepointspixelcentroidsinsidepolygons" so my points are ...
2
votes
1answer
121 views

Sample points based on multiple conditions

Can anyone suggest a QGIS/R approach to sample from a polygon n points that satisfy some conditions depending on underlying raster layers values? E.g. I have a country polygon and I would like to ...
2
votes
1answer
659 views

QGIS point sampling tool error in extracting values

I am trying to use the point sampling tool plugin from QGIS to get some sea ice data (ranging from 0-1) from a GTiff raster layer (ESPG: 3411) for my sites (ESPG:4326) in the Arctic. But the sea ice ...
2
votes
1answer
693 views

Deciding how many random sampling points needed for specific area?

I have a study area (forest) around 25he. I would like to randomly have sampling points (center of the sampling plots) there. How many points (plots) I need in related to the area of my case study? is ...
2
votes
1answer
24 views

Generating sampling points - making a series of points in the horizontal centre of a long polygon, equidistant spacing on vertical axis

I have a polygon showing the extent of a beach. I would like to create a series of sampling points along that beach, that are equally spaced north to south (say at increments of 100m to the northing ...
2
votes
1answer
288 views

How to sample points from temporal layerstacking image including null or masked value in Google Earth Engine?

I'd like to sample points from temporal Sentinel-2 images covering a state, about 13 month's mosaic image were stacked into a new image. When I sampled points on the image, I got nothing. I think ...
2
votes
1answer
723 views

QGIS 3.2 - Point Sampling Tool error

I am using "Point Sampling Tool" in QGIS 3.2 to obtain values from a raster file to a point layer. After selecting the layer with the points, the values to get values from, and defining the Output ...
2
votes
1answer
3k views

QGIS 2.6 - Point Sampling Tool plugin producing empty shapefile

I use a DEM file (*.tif) and a points layer. My need is basic : getting the Z value for each point by extracting them from the DEM. Both layers correctly opened with QGIS 2.6. The DEM returns a Z ...
2
votes
1answer
81 views

Applying distance/area dependent procedures in geographic coordinates over large areas?

I'm currently doing some niche modelling with data in geographic coordinates spanning all of Latin America. I am using R for my analysis. Some of the tasks I have to perform are area/distance ...
2
votes
1answer
639 views

Stratified Random Sampling by ID in QGIS?

I've been playing around with the Random Points tool in QGIS to realize stratified random sampling, but I'm running into a problem where I want my strata to be based on a polygon ID, not each ...
2
votes
1answer
141 views

Creating random plots with coordinates within polygon using R [closed]

I am trying to create random plots in a polygon shapefile and then to plot it with index no as 1,2,3,... along with a legend comprising XY coordinates corresponding to each index no. Code example: ...
2
votes
1answer
400 views

Extract row & column numbers of a raster at points in QGIS

Is there a tool in QGIS that will extract the row and column numbers of a raster at a set of points? All I have been able to find is the following: Raster Analysis > Sample raster values (Plugin) ...
2
votes
2answers
537 views

QGIS Point Sampling Tool: Invalid layer

I am completely new to GIS, and am trying to extract data from PRISM Climate data. I used the Point Sampling Tool in QGIS, but faced the following error: The new layer seems to be created, but is ...
2
votes
2answers
570 views

Stratified sampling from point data in ArcGIS Desktop?

I have 8000 points with a zipcode number. Actually those are tweet points talking about zipcode, so multiple points have same number (e.g. 300 points with zipcode 32,805). I want to get 800 sample ...
2
votes
1answer
1k views

Extracting spectral values from distinct points in ENVI Classic

I have 354 distinct points (as a shapefile) that are very close together i.e. 2-3 points have the same lat but different long or vice versa as the sampling was done in a very small area and the field ...
2
votes
0answers
405 views

How to import and point sample asc files on QGIS

I am trying to import .asc data into QGIS. These data are produced by the Stage Project in 2000. I want to import it into QGIS to allow me to point sample various climatic variables, especially ...
2
votes
1answer
54 views

Automatic extraction of manually selected points in ArcMap [closed]

I have an Orthomosaic and a DEM (both are in Geotiff formats and have RGB values) of a site, and I want to check their accuracy. For this purpose, I measured the 3D location (with mm accuracy) of some ...
2
votes
0answers
97 views

Sample Design for Kriging [closed]

I am taking soil samples on an agricultural plot and will be using the results as input to create a semivariogram for kriging in ArcGIS. This plot features raised planting beds in which the test crop ...
2
votes
0answers
578 views

Generating regularly spaced sample points in qgis based on ratio of area [closed]

I am generating sample locations in irregular shaped polygons in qgis. In my situation, there are often many polygons in one shapefile all with unique shapes that need a certain number of sample units ...
2
votes
0answers
670 views

GPS data cleaning and sampling of track data?

I have gotten a fairly large polyline-dataset of GPS-recorded tracks. I'd like to have a sample along the tracks for different variables. The problem is that the data has overlapping tracks. This ...
2
votes
2answers
716 views

Getting null values using Point sampling tool in QGIS 2.0.1 [closed]

I would like to obtain the information of a raster layer at some points. Apparently the Point sampling tool does the job. I have used this tool, and all the raster values extracted at specific points ...