Introduction to QGIS

Nils Ratnaweera

ZHAW School of Life Sciences and Facility Management
Institute of Natural Resource Sciences
Grüentalstrasse 14
8820 Wädenswil

+41 (0) 58 934 55 63
rata@zhaw.ch

Timetable

Lesson 1
Introduction and first steps
Raster and vector data
Lesson 2
Lesson 3
MCE and plugins in QGIS
Lesson 4
Sentinel data in QGIS
Inputs
(I talk)
Demos
(I show)
Exercises
(you do)
Workshops
(we do)

Why QGIS?



  • Widely used and very popular
  • Free and Open Source
  • Cross-platform (Windows, MacOS & Linux)
Widely used and very popular??
Source: ratnaweera.xyz/blog/2022-11-30-ArcGIS-vs-QGIS
Free and Open Source
  • Free as in free beer
  • Free as in free speech
Cross-platform

The transition will be hard
..brace yourselves

How is QGIS different from ArcGIS?



An opinionated side by side comparison
ArcGIS
QGIS
Point of contact
Single
none / multiple
Community
Weak
Strong!
Concept
Seamless
Modular
Documentation
Excellent
Very technical
User Interface (UX)
State of the art
Outdated
Compliance w/ OGC
Poor
High

First steps in QGIS



Workshop: First contact with QGIS

Coordinate reference systems and projections

Hi, where are you?
7:00
Campus Grüental, you?
7:05
Me too, where are you exactly?
7:07
10 meters south of the big tree
7:07
Here: 694138 / 230462
7:07
???
7:08
7:10
Source: map.geo.admin.ch 

                        CH1903+ / LV95:	   2'694'139.5, 1'230'462.0
                        CH1903 / LV03:	   694'138.66, 230'462.17
                        WGS 84 (lat/lon):  47.21838, 8.68150
                        WGS 84 (lat/lon):  47°13'06.186 N 8°40'53.383 E
                        UTM:               475'884, 5'229'482 (zone 32T)
                        MGRS 32TMT:        75884 29482
                        what3words:        opposing.vets.snoring
WGS84 is a Geographic coordinate system
Geographic Coordinate Systems

  • They see the world as a sphere
  • They use longitude and latitude
  • They are useful for global data
  • They are cumbersome for small-scale applications
  • The most important is WGS84
WGS84

EPSG
4326
West-East
-180 to +180
South-North
-90 to +90
West-East (CH)
5.9 - 10.4
South-North (CH)
45.8 - 47.8

                        CH1903+ / LV95:	   2'694'139.5, 1'230'462.0
                        CH1903 / LV03:	   694'138.66, 230'462.17
                        WGS 84 (lat/lon):  47.21838, 8.68150
                        WGS 84 (lat/lon):  47°13'06.186 N 8°40'53.383 E
                        UTM:               475'884, 5'229'482 (zone 32T)
                        MGRS 32TMT:        75884 29482
                        what3words:        opposing.vets.snoring
Projected Coordinate Systems

Projected Coordinate Systems

  • They abstract the world to a 2D-plane
  • They use x/y or E/N coordinates
  • They are useful for local (e.g. National) data
  • Cannot be used for global data
  • The most important (for us) are CH1903+LV95 and CH1903 LV03
CH1903+ LV95 (new swiss coordinate system)

EPSG
2056
West-East
2'400'000-2'800'000
South-North
1'100'000-1'300'000
CH1903 LV95 (old swiss coordinate system)

EPSG
21781
West-East
400'000-800'000
South-North
100'000-300'000

                        CH1903+ / LV95:	   2'694'139.5, 1'230'462.0
                        CH1903 / LV03:	   694'138.66, 230'462.17
                        WGS 84 (lat/lon):  47.21838, 8.68150
                        WGS 84 (lat/lon):  47°13'06.186 N 8°40'53.383 E
                        UTM:               475'884, 5'229'482 (zone 32T)
                        MGRS 32TMT:        75884 29482
                        what3words:        opposing.vets.snoring
UTM 32T / UTM 32 Nord

EPSG
32632
West-East
166'000
-
834'000
South-North
0-9'330'000
West-East (CH)
270'000 - 607'000
South-North (CH)
5'000'000 - 5'300'000


Demo: CRS in QGIS


Demo: CRS in QGIS (continued)
Break

Raster and vector data in QGIS

What is a geopackage?

Source: switchfromshapefiles.org
  • a better alternative to the limited and proprietery formats shapefile and geodatabase
  • can contain vector and raster data
  • can contain multiple layers


Demo: Vector Data in QGIS


Exercise: Import the other vector datasets from the geopackage into QGIS



Demo: Raster data in QGIS


Exercise:

Import the raster datasets into QGIS and play around with symobology



Break

Multicriteria analysis with QGIS

Finding suitable locations for wind turbines

Exclusion areas

  • Lakes
  • Settlement areas
Areas of interest

  • Low risk of icing
  • Easy access (existing road and low gradient)
Process model for ArcGIS Pro
The ArcGIS Pro way

ArcGIS vs. QGIS

Exercise: Complete the MCA
Class Slope (Degrees) Distance to Roads
1 >20 >2'000
2 15-20 1'500-2'000
3 10-15 1'000-1'500
4 5-10 500-1'000
5 0-5 0-500

QGIS Plug-ins

  • Vanilla QGIS is lightweight with limited features
  • Additional features are developped by the community
  • These features are implemented as "Plugins"
  • These plugins are made available via a central repository


Demo: Installing QuickMapService Plugin



Exercise: Install the QuickMapService Plugin

Break

Sentinel data in QGIS



Demo: Creating a true colour image from the red (4), green (3) and blue (2) bands


Exercise:

  1. Download sentinel data from Moodle
  2. Extract to reasonable location
  3. Create a QGIS Project in that same location
  4. Create an RGB image
  5. Optional: Create a NIR-GB image


Calculating the normalized difference vegetation index (NDVI).

... a simple indicator that can be used to analyse remote sensing measurements, assessing whether or not the target being observed contains live green vegetation.
NDVI ranges from -1 to +1 and is calculated as $\frac{\text{NIR}-\text{Red}}{\text{NIR}+\text{Red}}$


Workshop: Calculating NDVI

$\frac{\text{NIR}-\text{Red}}{\text{NIR}+\text{Red}}$

Bonus Workshop: Graphical Model Builder