Measuring data values at specific, discrete locations.

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2
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0answers
16 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
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1answer
28 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 ...
1
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0answers
43 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 ...
3
votes
1answer
57 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
66 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 ...
0
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0answers
22 views

Attempting to interpolate from samples rather than known observation. What kind of analysis is this?

I'm trying to figure out what the name of the kind of analysis I'm thinking of is, and what options in programs to check out (mainly ArcGIS or QGIS). I'm a bit of a beginner when it comes to ...
1
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0answers
42 views

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

this is my first post on Stack Exchange. The question I have involves generating sample locations in irregular shaped polygons in qgis. In my situation, there are often many polygons in one shapefile ...
0
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0answers
23 views

Assign Nodes ID to Polylines in QGIS

I want to consolidate data from various layers into a single layer so I can export it for use in an external software program. I am interested in how to selectively combine data from different ...
0
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1answer
60 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 ...
2
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2answers
79 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
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0answers
61 views

How to query a WMTS layer with a point layer in QGIS?

With the "identify" tool it is possible to query WMTS layers. Then, you can copy the acquired attributes and afterwards the clicked coordinates, then create a CSV file with attributes/coordinates. Is ...
2
votes
1answer
178 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 ...
0
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1answer
39 views

selecting a random sample of parcels

I am faced with the following issue. I got a raster map showing the position and extent of land parcels within a 35 sq Km area. The number of parcels is about 200. In anticipation of the following ...
1
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1answer
350 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 ...
2
votes
1answer
472 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
46 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 ...
1
vote
2answers
239 views

Using Spatial Analyst Sample tool

I have a bunch of rasters and a point file. I need the information from ll the raster files to be added to my points. My usual workflow is to use the Spatial Analyst sample tool. It works fine and ...
1
vote
1answer
269 views

Do I need to run regression in each samples separately?

I'd like to do smooth 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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1answer
29 views

RasterStack extract() for duplicated dates

I have a a Large RasterStack of temperatures and a 10570 points in a Large SpatialPointsDataFrame and I'm using extract() to assign the temperatures to each point in R. ...
0
votes
1answer
143 views

Point-sampling rasters using R? [duplicate]

I need to be able to sample many raster files (imported from GeoTIFFs) using a previously defined set of spatial points, using R. What's the best way to do this?
0
votes
1answer
588 views

how to choose stratified random sample on multispectral image

I'd like to choose random samples from multispectral image according to each Land Cover image. The multiband image has 70 bands representing land surface temperature data from MODIS. Land cover image ...
1
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0answers
221 views

GPS data cleaning - 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
351 views

Getting null values using Point sampling tool in QGIS 2.0.1

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 ...
18
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4answers
2k 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 ...
7
votes
3answers
861 views

R - How to sampleRandom() from large raster without NA values

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 ...
0
votes
2answers
74 views

Error point sampling tool

I'm usig QGIS 1.8.0 and I did some interpolations. Now I want to do some sampling with the point sampling tool but I keep getting this error (I attach a picture of the error message). Does anybody ...
2
votes
1answer
293 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 ...
0
votes
1answer
136 views

How to add information to an attribute table?

I'm working with qgis 1.8.0 and did the following: 1.-Divided my shapefile into 830 features (small rectangles). 2.- Added to my shapefile several points containing weather information using the "add ...
5
votes
0answers
98 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 ...
1
vote
1answer
411 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 ...
3
votes
1answer
697 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 ...
13
votes
1answer
4k 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 ...
7
votes
3answers
4k 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 ...
3
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0answers
309 views

Getting coordinates of pixels

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 ...
5
votes
1answer
1k 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 ...
3
votes
1answer
352 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 ...
12
votes
2answers
1k 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 ...
6
votes
1answer
1k 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 ...