QGIS | Spatial interpolation and fill nodata raster cells
> Objective
This section explains how to interpolate points in QGIS
This section shows how to interpolate points by using the nearest neighbour interpolation method
This section shows how to interpolate points by using the kriging interpolation method
The students will also learn how to add values to raster cells without values
> Index / Table of Contents
Introduction
Tutorial(s)
Nearest Neighbour Interpolation
Kriging interpolation
TIN interpolation
Fill no data raster cells
QGIS installation
> Summary and Highlights
Introduction
With spatial interpolation unknown values of points can be estimated by using points with known values. This section addresses the nearest neighbour interpolation method, which assigns point x with unknown value the value of the closest point y, the kriging interpolation method, which uses statistical models to predict the unknown value of point x, and the TIN interpolation, which is based on triangulation of data points. This section also covers how to fill raster cells without data.
Tutorial(s)
Nearest Neighbour interpolation
This method is the simplest approach to interpolation. The value of an attribute receives the value of the nearest neighbouring point.
Interpolate vector data to raster data using the Nearest Neighbour interpolation and Inverse Distance Weighting methods Hans van der Kwast: “Spatial interpolation in QGIS” Language(s): English Time: 15min 51s Chapters: Nearest Neighbor Interporlation (start-0:14), interpolations (0:14-0:37), interpolation tools (0:37-2:05), inverse distance (2:05-3:57), transparency (6:25-6:40), blending modes (6:40-8:17), interpret the results (8:17-10:13), 3d viewer (10:13-13:09), Nearest Neighbor (13-09-end) https://www.youtube.com/watch?v=By-K5C7jDQc
Interpolate temperature point data to raster using the Nearest Neighbour interpolation and Inverse Distance Weighting methods Hans van der Kwast: “Interpolate Points to Raster (Thiessen & IDW) in QGIS” Language(s): English Time: 7min 36s Chapters: clean up data (start-0:33), convert temperature to Celsius (0:33-1:15), remove table with temperature (1:15-1:55), interpolate to raster (1:55-2:48), inverse distance weight (2:48-end) https://www.youtube.com/watch?v=oiIVJdZqO8k
Control the output extent and spatial resolution with IDW, Nearest Neighbor interpolation and the graphical model from the PCRaster Resource Sharing repository Hans van der Kwast: “Nearest Neighbor Interpolation (Thiessen) in QGIS with Control of Extent and Resolution” Language(s): English Time: 5min 29s Chapters: introduction (start-1:02), grid (Nearest neighbour) tool (1:02-1:27), additional command line parameters for gdal_grid (1:27-2:53), add models from PCRaster resource sharing repository (2:53-4:14), Thiessen model from PCRaster repository (4:14-end) https://www.youtube.com/watch?v=r5vhPxeD-mo
Kriging Interpolation
This widely used interpolation method uses separate statistical models for each dataset to predict the attribute values.
Interpolate points to raster with kriging Hans van der Kwast: “Interpolate points to rasters with kriging in QGIS using the Smart-Map plugin” Language(s): English Time: 4min 17s Chapters: introduction (start-0:33), install Smart-Map plugin (0:33-2:03), interpolation with Smart-Map plugin (2:03-3:43), results (3:43-end) https://www.youtube.com/watch?v=-Vv1cAhiSVk
TIN interpolation
The TIN interpolation method is based on the triangulation of data points. The attribute values are determined by the values of the points that form the triangles in which they are placed. A linear interpolation is performed with these points to find the attribute values.
Create an elevation relief map and contours from field depth measurements for Lake Arlington in Texas Ujaval Gandhi: “Interpolating Point Data (QGIS3)”/”Interpoleren van puntgegevens (QGIS3)” Language(s): English, Dutch Chapters: overview of the task, get the data, procedure EN: https://www.qgistutorials.com/en/docs/3/interpolating_point_data.html NL: https://www.qgistutorials.com/nl/docs/3/interpolating_point_data.html
Fill no data raster cells
Sometimes there are raster cells without data. The following tutorials explain how to add values to them.
Interpolate voids (nodata pixels) in a Digital Elevation Model (DEM) Hans van der Kwast: “Interpolate voids in DEM for catchment delineation in QGIS” Language(s): English Time: 4min 56s https://www.youtube.com/watch?v=FwJSBoTn1y4
Replace NoData raster cells with values from other raster layers Hans van der Kwast: “Dealing with NoData in Discrete Rasters using QGIS” Language(s): English Time: 5min 31s Chapters: intro (start-0:48), hiding values for visualisation (0:48-1:52), assigning NoData values to rasters (1:52-3:10), calculating the number of data cells (3:10-4:16), replace NoData cells with values from other raster layers (4:16-end) https://www.youtube.com/watch?v=qApnkq7qsFU
Fill no data AHN file Erik Meerburg (Geogoeroe): “Gaten in een AHN-beeld opvullen (en er daarna nog even mee v” Language(s): Dutch Time: 6min 7s https://www.youtube.com/watch?v=e0bvqQPqi14
Fill no data AHN file Erik Meerburg (Geogoeroe): “Gaten in een AHN-beeld opvullen” Language(s): Dutch Time: 6min 15s https://www.youtube.com/watch?v=86xgzslcoAk
> QGIS Installation
Do you still need to install QGIS? The QGIS installation and update section explains how to install QGIS on Windows and macOS.
Useful Links
Hans van der Kwast YouTube channel
Ujaval Gandhi (QGIS Tutorials and Tips website)
Erik Meerburg (Geogoeroe) YouTube channel
#QGIS, #Interpolation, #Nearest Neighbour Interpolation, #Kriging Interpolation, #TIN interpolation, #Nodata values
Hans van der Kwast. (2021, April 30). Interpolate points to rasters with kriging in QGIS using the Smart-Map plugin [Video]. YouTube.