Questions tagged [sampling]
Measuring data values at specific, discrete locations.
105
questions
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1answer
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 ...
3
votes
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 "...
0
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0answers
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, ...
-1
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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 ...
0
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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 ...
0
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0answers
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 ...
1
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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:
...
0
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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 ...
3
votes
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 ...
1
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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 ...
1
vote
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, ...
0
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0answers
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,...
1
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0answers
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,...
1
vote
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
...
6
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0answers
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 ...
1
vote
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 ...
1
vote
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 ...
2
votes
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 ...
0
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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 ...
0
votes
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 ...
0
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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 ...
3
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0answers
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 ...
1
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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 ...
1
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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 ...
1
vote
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 ...
0
votes
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 ...
2
votes
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
votes
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) ...
0
votes
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 ...
2
votes
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 ...
3
votes
0answers
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 ...
0
votes
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%, ...
2
votes
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
votes
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 ...
0
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0answers
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 ...
1
vote
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 ...
0
votes
0answers
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 ...
2
votes
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 ...
9
votes
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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votes
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 ...
1
vote
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 ...
6
votes
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 ...
2
votes
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 ...
2
votes
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 ...
2
votes
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 ...
1
vote
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 ...
1
vote
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
votes
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 ...
