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Geographic Information Systems

Questions tagged [sampling]

Measuring data values at specific, discrete locations.

77 questions
info Newest Frequent Votes Active Unanswered
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0answers
18 views

rasterToPoints does not return PixelCenter (R)

My goal is to sample some coordinates that ly exactly in the center of a Landsat pixel. For this sampling, i use the clHs Unfortunately, my exported .gpx coordinates are not located in pixel-center, ...
2
votes
1answer
20 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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0answers
28 views

Sampling methods for training data and test data [closed]

I want to evaluate the species distribution model, and I have 8 continuous variables and 1 categorical variable (which is "covertype"). The code is like: samp<-sample(nrow(sdmdata), round(0.75*...
3
votes
0answers
30 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
16 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%, ...
1
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2answers
43 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
48 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
34 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
36 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
31 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 ...
0
votes
1answer
58 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 ...
3
votes
1answer
50 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 ...
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votes
1answer
83 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
42 views

Random Point generator - same every iteration? (ArcGIS 10.3.1)

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 ...
3
votes
1answer
293 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
233 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
99 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
87 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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votes
0answers
17 views

How Many Cells of Each Value Inside A Sampling Grid

I have a raster land cover data set, broken into 7 landcover types at 15x15m resolution, and my goal is to figure out how many of cells of each type are inside my sampling grid. I set up a sampling ...
1
vote
0answers
79 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
401 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
91 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
160 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 ...
1
vote
0answers
611 views

How to Create Random Points Within a Polygon (Vector Layer)

I have a vector layer that covers a few acres of land, with the buildings cut out (so essentially just the soil in the area). I want to generate points within this defined area. Later, I will use my ...
0
votes
0answers
52 views

Sampling Points and Areas around them

I have some coordinates in QGIS. I want to sample the values corresponding to those coordinates on a layer. I know that I can do that for the exact point using 'Point Sampling Tool'. Is there also a ...
2
votes
2answers
347 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
368 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 ...
1
vote
0answers
126 views

How to properly address autocorrelation for logistic regression of spatial data

Background for the Model: https://stats.stackexchange.com/questions/268201/how-to-increase-mcfadden-score-and-choose-proper-predictor-for-binary-logistic-r Data I have: Forest loss points Forest ...
2
votes
0answers
239 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
50 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 ...
4
votes
1answer
135 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 ...
3
votes
1answer
1k 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, ...
2
votes
1answer
863 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 ...
0
votes
1answer
99 views

Randomly placing polygon within delimited area in ArcGIS for Desktop?

I need to compare the number of animal species in a polygon of my study site against the number of species in a polygon of the same shape and size of my study site but located randomly within a ...
2
votes
1answer
467 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 ...
1
vote
2answers
482 views

Create transect lines of specific length through points

I've got a series of 30 random points in ArcGIS 10.3.1. I'm hoping to generate 200 meter lines of a specific orientation (i.e. north-south) through each point so that I can sample continuous raster ...
2
votes
1answer
524 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 ...
6
votes
1answer
336 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 ...
2
votes
0answers
92 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 ...
1
vote
0answers
657 views

Efficiently iterating through raster calculations with Rasterio or GDAL

I've got a very slow and round-about way to currently do this, but I struggle with the general concept of using windows in raster calculations and how to apply an affine or geotransformation between ...
3
votes
3answers
209 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
352 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 ...
1
vote
1answer
94 views

Getting NULL-values when point sampling USGS (SRTM 1 Arc-Second Global) grid (QGIS 2.8.2)

I use the Point Sampling Tool in QGIS to transfer gridvalues (of DEMs) to point features. This goes well with grids from f.i. MapMart (SRTMHARRIS_DEM), but I get only NULL-values when using grids from ...
3
votes
2answers
1k 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
162 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 ...
1
vote
1answer
834 views

Receiving NULL values from Point Sampling Tool in QGIS

I am using QGIS 2.8.2. My project includes a raster layer of flow depth representing the output from a flood simulation (.DAT file). It also includes a vector layer of points representing the ...
2
votes
0answers
513 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 ...
1
vote
1answer
162 views

Sampling one shapefile with polygons of another using R?

I have two shapefiles that partially overlap. One (the bigger one) consists of several polygons which represent fields I am interested in. The second, is a rectangular shape that overlaps about 30% of ...
3
votes
2answers
822 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. ...
0
votes
2answers
78 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 ...

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