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There’s a good chance you’ve done something today that used a sliding window (also known as a moving window) and you didn’t even know it. Have you done any photo editing? Many editing algorithms are based on moving windows. Do you do terrain analysis in GIS? Most topographic raster metrics (slope, aspect, hillshade, etc.) are…
Filling NumPy arrays with a specific value is a typical task in Python. It’s common to create an array, then initialize or change some values, and later reset the array to a starting value. It’s also common to initialize a NumPy array with a starting value, such as a no data value. These operations may…
When you work with spatial data it’s inevitable that you will need to implement information from both a vector and raster data source for the same location. This task can easily be accomplished manually, but it often becomes quite cumbersome when the process must be automated across a large number of features, time periods, and/or…
It is a common need to summarize information from a gridded dataset within an irregularly shaped area. While at first glance this may seem simple, reconciling differences between raster (gridded) and vector (polygon) datatypes can quickly become complicated. This article shows how to implement a zonal statistics algorithm in Python in 4 steps. Load raster…
Gridded, spatial data are commonly stored in NetCDF files. This is especially true for climate data. NetCDF files offer more flexibility and transparency than some traditional raster formats by supporting multiple variables and detailed metadata. Because of the metadata and file structure NetCDF files can be more difficult to access than traditional raster formats. This…
Aerial imagery is used for purposes ranging from military actions to checking out the backyard of a house you might buy. Our human brains can easily identify features in these photographs, but it’s not as simple for computers. Automated analysis of aerial imagery requires classification of each pixel into a land cover type. In other…
Did you know you can write parallel Python code that will run on your laptop and on a super computer? You can, and it’s not as difficult as you might expect. If you already write code for asynchronous parallelization then you won’t even have to do much restructuring. High Performance Computing (HPC) distributes pieces of jobs across…
A flexible method to speed up code on a personal computer Do you wish your Python scripts could run faster? Maybe they can. And you won’t (probably) have to buy a new computer, or use a super computer. Most modern computers contain multiple processing cores but, by default, python scripts only use a single core….
Many geographic data are store in netCDF format. This is especially true for climate data. Interacting with netCDF data files is an important skill for any geographer, physical scientist or data scientist to have. This tutorial will get you started using the netCDF4 Python package to read netCDF data. First, you’ll need to install netCDF4….
Use the random forests algorithm to classify image segments into land cover categories. This post is a continuation of Geographic Object-Based Image Analysis (GeOBIA). Herein, we use data describing land cover types to train and test the accuracy of a random forests classifier. Land cover data were created in the previous post. Step-be-step video instructions…
It is very simple to clip vector layers with PyQGIS. This tutorial will demonstrate how to use Python in QGIS to clip a line layer with a polygon layer. First, import the processing module and set the paths to the line, polygon and output layers. The next step is to run the clip tool. This…
This tutorial will walk you through segmenting and classifying high resolution imagery using Python. Part 1 of this tutorial teaches how to segment images with Python. After you have completed Part 1, Part 2 will teach how to use machine learning methods to classify segments into land cover types with Python. YouTube videos give step-by-step…
This tutorial will demonstrate how to measure the distance between two geometries in QGIS using Python. First we will measure the distance between points in the same layer. Then we will measure the distance between features in a points layer and a lines layer.
Creating a buffer around features is a common spatial analysis task. This blog post demonstrates how to customize and automate buffer operations with Python in QGIS (PyQGIS).
A common operation with vector layers is to select features based on attribute values and save those features to a new vector layer (i.e. shapefile). This tutorial will walk you through how to create a new shapefile from selected features. We’ll select some features, then save those features to a new shapefile. First, we’ll open…
In this tutorial, we’ll walk through how to create a shapefile from scratch with the QGIS Python (PyQGIS) API. You shouldn’t need to do this, but if you’re running into problems where functions don’t show up you can import the qgis module at the beginning. This usually isn’t a problem but there have been a…
With the PyQGIS API you are able to use Python in QGIS to automate the creation of map layouts. There are two reasons this is really awesome! First, once you’ve written the initial code to set up the map, you can change map symbology or map layers and exactly replicate layout. Second, once you have…
This tutorial will teach you how to render (print or save) a QGIS layer as an image using the PyQGIS Python API. Automating layer rendering can be very useful to create and save visualizations that have consistent styling, extent and format. The first thing you need to do is create a QImage. Here we create…
In a previous tutorial I showed you how to access raster values and data with the Geospatial Data Abstraction Library (GDAL). This tutorial will show you how to create a raster with GDAL. Start by importing the gdal and osr Python modules. The osr module is used for handling spatial references. Also import numpy. Now…
PyQGIS has some methods for accessing single values in a raster, but the best way to access raster data is using the Geospatial Data Abstraction Library, or GDAL. GDAL comes pre-installed on the QGIS Python interpreter, so if you access the Python interpreter from QGIS (Plugins > Python Console) you won’t have to install any…
Deleting features is a common operation in QGIS. It is easy to automate this task with Python, allowing you to quickly delete features based on any conditions you set. First, select the layer from which you want to delete features. This line of code will select the first layer with the name ‘layer name’. You…
Geometry is what defines the shape and spatial location of a feature. Features can be points, lines, or polygons, can be anywhere on earth, and can be represented by coordinates in a number of different units (depending on the coordinate reference system, or projection). Points are represented by a single coordinate pair while lines and…
The QGIS Python API (PyQGIS) makes it possible to automate creation of point features. This tutorial will show you how to add features to an existing shapefile. For this example we will assume the layer containing the point features is already opened in the QGIS table of contents. First, we save all layers with a…
It is tedious, and not practical, to manually type in values for array creation. In this tutorial we will go through methods for automating array creation and importing tabular data into numpy arrays. Creating empty arrays With numpy you don’t actually create an ‘empty’ array. But you can create an array without intializing specific values. This can be useful…
We’ve gone through the basics to manually create arrays of different dimensions and shapes. There will be times that you will want to query array shapes, or automatically reshape arrays. This tutorial will show you how to use numpy.shape and numpy.reshape to query and alter array shapes for 1D, 2D, and 3D arrays. Different methods are required to find…
Creating a simple array After numpy is installed, we can begin to create arrays. First, we’ll need to import numpy into our python project. Here I use the statement, import numpy as np, to limit my typing later. This code will allow me to use np in my script to represent instead of typing the full numpy everytime. Then, we can create a simpy…
Check Installation First, check to see if you already have numpy installed. From the terminal, you can use pip to do this. If numpy is installed you will get output similar to this. If numpy is not installed no output will be shown. Install numpy numpy can be installed simply using pip. Check version You can check the numpy version using pip show as demonstrated above. Video tutorial This…
Requirements: Python version 2.7 or greater Beginner skills with python Desire to learn numpy Objectives: Teach the basics of using numpy in python Provide data science applications of numpy Introduce advanced numpy concepts What is numpy? numpy is a powerful python package for handling arrays. It uses C libraries to optimize procedures that would otherwise be slow/computationally expensive in python. What can I do…
Objectives: Select features from a vector layer Iterate over selected features Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write…
Objectives: Retrieve data from the vector attribute table Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write code in the…
Objectives: Get statistics for a raster band Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write code in the editor…
Objectives: Get information from layers that have already been added to the QGIS interface Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I…
Objectives: Query the value of a raster layer at a points Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I prefer to write…
Objectives Load and symbolize a vector layer with pyqgis Apply basic and graduated symbology Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into the console, or select the pad and paper icon to write code in the editor. I…
More information can be found in the PyQGIS Developer Cookbook. Requirements QGIS version 3.0, or greater Objectives Load and symbolize a raster layer with pyqgis Get statistics from a raster band Open the QGIS Python Console From the menu, select Plugins -> Python Console, or Ctrl + Alt + P (Windows) You can type directly into…
