Vladimir Rybalko vladimir-rybalko

Interpolate points along lines using QGIS virtual layers

Suppose we want to interpolate a number of points along each line in a layer:

We have a column called stations that specifies how many points to interpolate on each line:

How to setup a NASA WorldWind elevation server

Introduction

This guide shows how to create a WMS server on a local VM using Apache, MapServer and elevation data sets curated by NASA. This WMS server serves as a model for a production MapServer instance to be deployed on an a network.

The guide contains a brief overview of how the WorldWind clients make requests, followed by instructions for setting up the Apache web server, MapServer and the Apache caching.

Making a big image zoomable

When you have a giant image and you want to make it easy to pan and zoom without downloading the whole 50MB image into someone's browser, a nice workaround is to cut that image into tiles at different zoom levels and view it as it were a map. An example where I've used this technique is The "Snowpiercer" Scenario.

One way to cut your big image into the requisite tiles is with gdal2tiles.py.

Alternatively, this Node script will do the cutting after you install node-canvas and mkdirp:

const fs = require("fs"),

Crawling Anonymously with Tor in Python

adapted from the article "Crawling anonymously with Tor in Python" by S. Acharya, Nov 2, 2013.

The most common use-case is to be able to hide one's identity using TOR or being able to change identities programmatically, for example when you are crawling a website like Google and you don’t want to be rate-limited or blocked via IP address.

Tor

Install Tor.

	import json
	import geojson
	from shapely.geometry import shape

	o = {
	"coordinates": [[[23.314208, 37.768469], [24.039306, 37.768469], [24.039306, 38.214372], [23.314208, 38.214372], [23.314208, 37.768469]]],
	"type": "Polygon"
	}

	s = json.dumps(o)

	import asyncio
	import psycopg2

	# dbname should be the same for the notifying process
	conn = psycopg2.connect(host="localhost", dbname="example", user="example", password="example")
	conn.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)

	cursor = conn.cursor()
	cursor.execute(f"LISTEN match_updates;")

	#
	apt-get install openjdk-8-jre

	# PostgreSQL and PostGIS
	apt-get install postgresql postgresql-contrib postgis postgresql-10-postgis-2.4

	# Create "geoserver" database
	sudo -u postgres createuser -P geoserver
	sudo -u postgres createdb -O geoserver geoserver
	sudo -u postgres psql -c "CREATE EXTENSION postgis; CREATE EXTENSION postgis_topology;" geoserver

	/* Time zone used from your Google Callendar */
	FORM_OPEN_DATE = "2014-12-20 08:00";
	FORM_CLOSE_DATE = "2014-12-25 23:30";
	RESPONSE_COUNT = "100";

	/* Init the from and set triggers */
	function Initialize() {

	deleteTriggers_();