Questions tagged [sampling]

Measuring data values at specific, discrete locations.

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3
votes
1answer
29 views

How to randomly select point within grid (QGiS)

I have a series of occurrence points that I am trying to downsample to 1/20 km to avoid sampling bias. So far, I have made a grid of ~20km squares and have filtered them down to squares with more than ...
1
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1answer
52 views

Cut hole in raster with shapefile and sample at closest edges

I have a raster in which I'd like to cut a "hole" with a shapefile. I have points close to the boundary, but inside the hole, and I would like to find the closest point on the edge. To give a concrete ...
0
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1answer
95 views

GEE: Select random sample on known-NDVI-range for supervised classification

I intend to get random samples for training the supervised classification in Google earth engine. The code here, for example, I calculate NDVI and mask out NDVI < 0.65 (i.e. NDVI >= 0.65 is ...
1
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1answer
99 views

Getting properties of random points in Google Earth Engine

I want to have random points across Peru and their properties (the band values of IMAGE) for statistical analysis in GEE. I found two options which are sampling and random points. I have tried the ...
1
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1answer
51 views

How to sample points on specific landcover class using Image.stratifiedSample in Google Earth Engine?

I need to sample NDVI time series on the crop classe defined in the Copernicus GLDAS Landover dataset (value: 40). The logical approach seems to be using Image.stratifiedSample on the landcover, ...
6
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0answers
82 views

How does Empirical Bayesian Kriging of ArcGIS Pro 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 ...
6
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3answers
3k 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 ...
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0answers
27 views

Generating random points with overlapping polygons in QGIS

The "Random points inside polygons" tool in QGIS works great to generate a fixed number or density of points within polygons; however, because QGIS does not link the polygon ID to the points,...
3
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1answer
889 views

Running regression in each sample separately?

I'd like to smooth an NDVI image by regression analysis; response of time series NDVI image to Julian date to represent the seasonal changes in NDVI as a function of Julian day. The time series NDVI ...
1
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0answers
13 views

What is the minimum sample size when sampling spatialy from existing points [closed]

I have sampled points from an existing shapefile using the Generate Near Table proximity feature to calculate the distance that I later used to select points. Depending on the distance interval I used,...
1
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1answer
66 views

Unpack error occuring when sampling raster values to points with rasterio

I'm new to Python. I'm trying to sample raster values to points based on the geometries of a shapefile using the below code but I'm receiving the below error . import fiona import rasterio as rio ...
54
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5answers
15k 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 ...
1
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1answer
132 views

Is it possible to read a subset of points with the PDAL C++ api?

I am using the PDAL C++ API to read LAS/LAZ data. We're finding some of the tile files are very large (160M+ points), so I wish to take a sample of them. Although the point order in the tiles is ...
0
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0answers
23 views

How to get matched pairs from CEM

I am using Coursened Exact Matching to improve balance in my sample. The summary matching results after applying CEM are that 11,128 pixels have been matched: Sample sizes: Control Treated ...
0
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0answers
16 views

Sample strategy to model continuous variable from conglomerate ground sample units

I´m using data from the Brazilian national forest inventory to model forest canopy metrics with Landsat imagery. The sample units have this conglomerate configuration (picture), which creates a ...
1
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1answer
162 views

Extracting different number of points for different class in GEE

I want to write a function that takes class id and number of points for each class as argument and samples points from polygons, returning a FeatureCollection. I could only write a function that ...
0
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0answers
24 views

Google Earth Engine: Collecting Region Samples through image collection and merge them

I am using S1 Imagecollection to start a temporal supervised classification. Firstly, I added polarimetric indexes and other data as bands in each image. Then, I filtered the image collection and got ...
2
votes
1answer
27 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 ...
0
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1answer
34 views

Non-random sampling of point vector layer in QGIS

I have a point vector layer with 47.000.000 points representing elevation. It is a regular grid with constant spacing. I aim for rasterization but it is very slow. I know how to do random sampling but ...
0
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1answer
579 views

How to solve “Collection query aborted after accumulating over 5000 elements”?

I am trying to sample image and to get scatter plot of its' two bands- NDVI and db from senttinel 1. For some reason, probably because of the size of the shapefile, I get the error: Error ...
2
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0answers
95 views

Raster layer stacking and extracting values at points with PyQGIS

I have a dozen single band raster layers in the same CRS overlapping perfectly. I would like to 'stack them one on the other' and extract values at point locations (from a CSV). After that the ...
0
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1answer
509 views

Exporting dataframe - used reduceRegion to sample an image in Google Earth Engine

I am trying to sample the Global Forest Change dataset using randomly drawn points and the reduceRegion function. The way I construct this is: var sampledPoints = gfc2014_c.reduceRegions({ ...
1
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0answers
288 views

Stratified sampling in Google Earth Engine

I am trying to get stratified random points out of GHSL (Global Human Settlement Layer) which is a classified raster over my study area (partially Europe and Asia continent), see the picture below. I ...
1
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1answer
127 views

ArcGIS Random Point generator producing same points every iteration

I am generating random points to sample within a stratum. Data Management Tools > Feature Class > Generate Random Points This works just fine, except that I noticed the points I generated for ...
1
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1answer
692 views

Google Earth Engine - how to set masked pixels to 'noData'

Lets say I have a region of mangrove forests (from a classified Landsat image) and I mask out all non mangrove pixels. I view this as a layer on the map and it shows the mangrove forests on the map ...
0
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2answers
74 views

Random sampling in ArcGIS Desktop

I have 14,033 points representing the location of some weather stations across the 36 states in Nigeria. I want to use an ArcGIS Desktop sampling tool to implement a random selection of 200 points ...
1
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1answer
56 views

Create point clusters based on grid

I am trying to make a systematic cluster sampling pattern for data collection. The sampling consist of the points placed over the landscape in 6 km span (red). From this major point, I need to create ...
2
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0answers
718 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
1answer
343 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: ...
9
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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 ...
4
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2answers
3k 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 ...
2
votes
1answer
728 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) ...
0
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1answer
590 views

Export pixel neighborhood in Google Earth Engine [closed]

I have some points and know how to extract the Landsat data at these points and build and export a training dataset to feed an external classifier. But how can I efficiently and automatically build a ...
2
votes
1answer
694 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 ...
3
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0answers
196 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 ...
19
votes
2answers
11k 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 ...
2
votes
1answer
452 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 ...
0
votes
1answer
52 views

Sampling land cover map using ArcGIS Desktop?

I have a little bit of a sampling problem in ArcGIS Desktop. I have a classified map with 7 Landcover classes, and this classes are as follows with their percentage: Forest=20.9%, agriculture=6.3%, ...
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
2answers
511 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 ...
0
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0answers
864 views

How can I sample points from images mosaic in Google Earth Engine

Rodrigo E. Principe did a great job for Mosaicking a Image Collection by Date (day) in Google Earth Engine (https://code.earthengine.google.com/20ad3c83a17ca27b28640fb922819208) based the code, I ...
6
votes
1answer
2k 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 ...
1
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1answer
50 views

Automating point feature class placement inside polygons using specific parameters?

I am trying to generate a point feature class of possible plot centers for a research project. The plot centers will be inside of defined forest stand polygons which are aggregated in various ways ...
0
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0answers
99 views

QGIS spatial sampling tool for existing points within a polygon ensuring even spread

I would like to spatially sample 10 existing points from within a polygon. I have read the answers from "QGIS point sampling tool really slow for polygons?"; "points within a polygon" as well as "How ...
-2
votes
1answer
243 views

Stratified random point sampling in Python

I have a very basic knowledge in Python and arcpy. I want to create a stratified random sampling point on a continuous polygon. So far, I have dissolved the polygon (according to categories) and ...
3
votes
1answer
201 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 ...
1
vote
1answer
922 views

Create random sampling point in each grid's cell

I would like to know how to create an X number of random points in each grid cell. I'm using data from a DEM layer, which contains information about elevation. I used this information to obtain slope ...
0
votes
2answers
81 views

ArcGIS 10 sample selection

I am using ArcGIS 10 and I would like to select (in a manner of well spatially distributed) some of the polygons included in a shapefile as testing population for a statistical analysis. The rest of ...
2
votes
1answer
864 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 ...
1
vote
1answer
236 views

How much do leaves on/off affect the number of LiDAR ground returns?

We would like to collect a generic purpose topographic LiDAR dataset over a large region in Belgium. Our minimum requirement is to achieve at least 1 point/m² on the ground. Ideally, we would like to ...