Questions tagged [sampling]

Measuring data values at specific, discrete locations.

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59 views

Sampling raster data around point set in QGIS

I have the following problem: I have a set of 27 "destinations" which I have selected manually and saved as a POINT layer. I have loaded several raster data layers into my project (with ...
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1answer
68 views

Randomly sample features from polygon layer with the condition that sampled features will be non-adjacent

Problem: I have a polygon vector layer with potential sample plot locations across a larger ROI. Using python's geopandas, I can randomly select a subsample of polygons from the layer based on the ...
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1answer
26 views

Stratified random sampling from raster in ArcMap

I've been conducting accuracy assessment of my classification result. I have a single band raster with 6 classes (1 to 6 values in cells of the raster). How can I generate random points as "...
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6 views

Raster sampling: Extracting values from multiband-raster only if no clouds at the sampling points acc. to the Quality-bit-layer (QAI) QGIS 3, Win10

I'd like to extract band values at given points out of a timeseries of tiled Sentinel2-derived 10-band-gtiffs with bottom-of-atmosphere reflectance information (BOA). On the whole there are 6 tiles, ...
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1answer
38 views

How to perform Statified random sampling for supervised classification

I want to select my training points using stratified sampling. When I run the code, there is an error saying "unrecognized argument". Can someone look at my code and help me find the issue ...
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1answer
41 views

How fast GPS position estimates fluctuate?

I wonder how fast the GPS position estimates generally change over time for a stationary receiver. I want this information to form some idea around what the sampling rate needs to be to estimate the ...
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11 views

Raster sampling of time series: Creating one single value-table including all values from all record dates by one single batch process

I have a Sentinel time series of about 25 rasters with different record dates. Area of interest are several sections/sites of a river floodplain. The tiffs contain for each pixel the reflection values ...
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1answer
24 views

Optimize sampling on band 1 of a big dataset

We do MANY samplings on band 1 of a big dataset, using rasterio dataset.sample function. (https://github.com/mapbox/rasterio/blob/master/rasterio/sample.py) Our python code looks something like this: ...
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2answers
65 views

Sampling points in R with both distance constraint and group

I have a spatial point data frame with categorical variable as a column named "type", I would like to draw a random sample from these points (let's say 100 points) with maximum and minimum ...
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1answer
83 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 ...
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1answer
211 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 ...
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1answer
86 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, ...
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53 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,...
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15 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,...
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1answer
89 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 ...
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107 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 ...
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1answer
189 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 ...
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1answer
265 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 ...
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1answer
28 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 ...
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1answer
139 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 ...
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1answer
37 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 ...
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1answer
862 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 ...
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146 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 ...
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1answer
786 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({ ...
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0answers
375 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 ...
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1answer
61 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 ...
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1answer
70 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 ...
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2answers
90 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 ...
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1answer
458 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
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1answer
914 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) ...
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1answer
708 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 ...
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1answer
824 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 ...
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224 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 ...
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1answer
58 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%, ...
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2answers
611 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
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1answer
558 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 ...
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1k 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 ...
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1answer
52 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 ...
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107 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 ...
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1answer
825 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 ...
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1answer
2k views

What is 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 ...
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1answer
272 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 ...
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1answer
141 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 ...
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3answers
4k 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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1answer
942 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 ...
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1answer
280 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 ...
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1answer
135 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 ...
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0answers
117 views

Applying mask to Kriging shape in ArcGIS Desktop?

I'm trying to apply an mask to a Kriging image for after apply a Density Sampling Network, but unfortunately I'm not getting good results. I tried to apply on mask on Density Sampling Network and is ...
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1answer
1k 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 ...
3
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1answer
235 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 ...