Difference between revisions of "AfricaEvents27June2009"

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(worked in updated programme)
Line 83: Line 83:
 
GRASS is a sophisticated standalone GIS package which can also be accessed through QGIS. It installs with QGIS by default.  
 
GRASS is a sophisticated standalone GIS package which can also be accessed through QGIS. It installs with QGIS by default.  
  
−
R is a comprehensive statistics package that can be also accessed through QGIS.  
+
You can use GRASS functions from QGIS
 +
 
 +
by using the GRASS plugin from the plugin manager:
 +
 
 +
Plugins/Manage plugins/GRASS
 +
 
 +
This places a new toolbar on your QGIS interface.  Click on the first icon
 +
 
 +
(the folder with a grass stalk) to open the prepared GRASS mapset, which is a  
 +
 
 +
collection of maps. 
 +
 
 +
There are three entries needed in the box that opens up:
 +
o Gisdbase
 +
o Location
 +
o Mapset
 +
 
 +
These should be set to:
 +
o home/tim/Grassdata
 +
o training_jhb
 +
o analysis
 +
 
 +
Then click OK to open the mapset.
 +
 
 +
Ask for help from one of the presenters if making these choices is confusing
 +
for any reason.
 +
 
 +
Once this is done, you may use the icons with the '+' symbol to add vector
 +
and raster maps from the GRASS database.  You may use the QGIS context-sensitive menu (right-click) to remove layers if you do not want to see them.
 +
 
 +
Now open the prepared QGIS project analysis.qgs to see many of the map layers
 +
 
 +
available in GRASS. We are going to use the GRASS toolbox to find answers to
 +
some questions that GIS can help us with.
 +
 
 +
Click on the tools icon on the GRASS toolbar to open the GRASS tools window.
 +
 
 +
It has three tabs at the to:
 +
o Modules Tree, which has a list of GRASS modules grouped according to their function, rather like a Windows Explorer view of directories.
 +
o Modules List, which has a long list of modules.  Type the beginning of a modules name in the box at the bottom to find it rapidly.
 +
o Browser, which shows you the GRASS map layers grouped into raster and vector groups.
 +
 
 +
If you pick a map layer in the pane on the left, you will see descriptive
 +
information about the layer in the pane on the right.  Try this with raster
 +
and vector layers, and notice that the information given is different for the
 +
two types. 
 +
 
 +
You can leave the GRASS Tools window open while you are working with QGIS. 
 +
 
 +
2. Why is it so noisy here?
 +
 
 +
At the end of a long day, you want to put your feet up and relax.  But the noise from the freeway just never stops!  How many houses in the area are close enough to a major road to be badly affected by noise?
 +
 
 +
The noise from the freeway will travel further than the noise from a suburban
 +
road. Luckily, we already have distances entered against types of road in the Roads map layer.
 +
 
 +
Open the attribute table and have a look.
 +
 
 +
2.1 To start the analysis, go to the modules tree and select the module Buffer, under:
 +
 
 +
Vector/Spatial analysis
 +
 
 +
Another tab will open to allow you to run the Buffer module.
 +
 
 +
Select the map layer Roads as input. 
 +
 
 +
......  go to Linux for other detail:
 +
  select attrib for Buffer
 +
 
 +
Enter Roads_buffer as the name of the output layer.
 +
 
 +
Then press Run.
 +
 
 +
The progress bar at the bottom will show you how much longer you have to wait.  When it is finished, click on View output to show the result in QGIS.
 +
 
 +
See how the buffers are wider around the freeway than around the main roads.
 +
 
 +
Tip: You can close the tab for the module using the Close button next to View output.
 +
 
 +
2.2 Now we want to see how many houses are affected.  We have the erven outlines rather than houses, but it will be a good approximation.
 +
 
 +
Click on the Modules List tab, and type "v.select" at the bottom.  The v.select.overlap module should appear at the top.  Click on the module name to open it.
 +
 
 +
Select Erven as the first input map layer.
 +
 
 +
Select Roads_buffer as the second input map layer.
 +
 
 +
Enter Erven_noise as the output map layer.
 +
 
 +
Click on Run, and View output.
 +
 +
This will show you all erven overlapping the noise buffer that we created. 
 +
 
 +
Open the attribute table and scroll down to the bottom to see how many houses are affected.
  
 
== Audience Selections ==
 
== Audience Selections ==

Revision as of 04:43, 26 June 2009

...back to Africa_Local_Chapter

Introduction to QGIS

What?

Our second OSGeo local chapter meet up! We will chew the cud, show you some cool stuff and start to get people familiar with the brilliant FOSS GeoSpatial products out there, specifically QGIS on this occasion!

We'll go through installing QGIS and getting it to a point where you can have fun (and get your job done) with it.

How Much?

There will be a door charge of R250 to cover costs, lunch and refreshments. That and an open mind are all you need to bring.

Where?

St Davids Marist Inanda College
36 Rivonia Rd
Inanda
Sandton

Map and Directions

NB: We'll be in the Prep School computer lab.

When?

  • Saturday June 27th 2009
  • 08h30 to 15h30
  • includes lunch and refreshments

Who

Your friendly presenters for the day will be:

  • Tim Sutton (tim at linfiniti.com) - QGIS hacker and FOSS GIS junkie extraordinaire. Tim eats Weetbix for breakfast because it sounds like Linux. He once rewrote Nkosi Sikelela in C++ because he was feeling patriotic.
  • Graeme McFerren - (graeme.mcferren at gmail.com) - GIS researcher and FOSS4G user. Mmm, aspire to be like Tim then.
  • Gavin Fleming (gavinjfleming at gmail dot com) - I enjoy my daily FOSS4G fix. I'm a 'geoinformation scientist' at Mintek and love to see cutting edge and useful geospatial applications emerging, especially when they're based on FOSS.
  • Brendon Wolff-Piggott - (brendon at integratedgeodata.co.za) - Water resources consultant and FOSS GIS enthusiast. I wish there were more hours in the day to keep up with FOSS4G!

RSVP

Let gavinjfleming at gmail dot com know if you're coming as numbers are limited.

Programme and notes

  • Be there in time for a 8h30 start
  • Computers are provided. All you need to bring is R250!
  • It doesn't matter what level you are.
  • The programme is subject to change and participant input right to the last minute!

Intro to the QGIS project - Tim

First tour of the User Interface - Brendon

Advanced symbolisation - the renderer types, labelling and map actions - Brendon

Loading and viewing data - common data formats, symbolisation. Tips and tricks to enhance image display.

Making your first project - Graeme

- adding layers and saving a project

Map Production - Gavin

  • Tea

Data capture - editing local and PostGIS datasources - Tim

Projection basics - Gavin

  • Lunch

QGIS plugins - Graeme

QGIS and Web GIS WMS and WFS clients - Graeme

Advanced analysis with QGIS

Plugins - Carson Farmer's plugins with R, etc - Gavin

  • break

GRASS - Brendon

GRASS is a sophisticated standalone GIS package which can also be accessed through QGIS. It installs with QGIS by default.

You can use GRASS functions from QGIS

by using the GRASS plugin from the plugin manager:

Plugins/Manage plugins/GRASS

This places a new toolbar on your QGIS interface. Click on the first icon

(the folder with a grass stalk) to open the prepared GRASS mapset, which is a

collection of maps.

There are three entries needed in the box that opens up: o Gisdbase o Location o Mapset

These should be set to: o home/tim/Grassdata o training_jhb o analysis

Then click OK to open the mapset.

Ask for help from one of the presenters if making these choices is confusing for any reason.

Once this is done, you may use the icons with the '+' symbol to add vector and raster maps from the GRASS database. You may use the QGIS context-sensitive menu (right-click) to remove layers if you do not want to see them.

Now open the prepared QGIS project analysis.qgs to see many of the map layers

available in GRASS. We are going to use the GRASS toolbox to find answers to some questions that GIS can help us with.

Click on the tools icon on the GRASS toolbar to open the GRASS tools window.

It has three tabs at the to: o Modules Tree, which has a list of GRASS modules grouped according to their function, rather like a Windows Explorer view of directories. o Modules List, which has a long list of modules. Type the beginning of a modules name in the box at the bottom to find it rapidly. o Browser, which shows you the GRASS map layers grouped into raster and vector groups.

If you pick a map layer in the pane on the left, you will see descriptive information about the layer in the pane on the right. Try this with raster and vector layers, and notice that the information given is different for the two types.

You can leave the GRASS Tools window open while you are working with QGIS.

2. Why is it so noisy here?

At the end of a long day, you want to put your feet up and relax. But the noise from the freeway just never stops! How many houses in the area are close enough to a major road to be badly affected by noise?

The noise from the freeway will travel further than the noise from a suburban road. Luckily, we already have distances entered against types of road in the Roads map layer.

Open the attribute table and have a look.

2.1 To start the analysis, go to the modules tree and select the module Buffer, under:

Vector/Spatial analysis

Another tab will open to allow you to run the Buffer module.

Select the map layer Roads as input.

...... go to Linux for other detail: 

 select attrib for Buffer

Enter Roads_buffer as the name of the output layer.

Then press Run.

The progress bar at the bottom will show you how much longer you have to wait. When it is finished, click on View output to show the result in QGIS.

See how the buffers are wider around the freeway than around the main roads.

Tip: You can close the tab for the module using the Close button next to View output.

2.2 Now we want to see how many houses are affected. We have the erven outlines rather than houses, but it will be a good approximation.

Click on the Modules List tab, and type "v.select" at the bottom. The v.select.overlap module should appear at the top. Click on the module name to open it.

Select Erven as the first input map layer.

Select Roads_buffer as the second input map layer.

Enter Erven_noise as the output map layer.

Click on Run, and View output.

This will show you all erven overlapping the noise buffer that we created.

Open the attribute table and scroll down to the bottom to see how many houses are affected.

Audience Selections

Tell us what else you'd like to try.

Show off session

Here we can do some whizz bang demo stuff that we don't have time to do in workshop format but that will give you some hints as to what else can be achieved.

e.g. Terrain modelling and drapes.

General

Questions and answers. What you can do next. Resources. Possibly some in-depth examples based on frequent questions. What would you like to see at future workshops?

Possible Extras

  • Introduction to the Python console
  • The Python API

Your assessment of the workshop

Tell us what you thought!

PS: Where to get free spatial data? Surveys and Mapping, Demarcation Board, OpenStreetMap, GPS, etc. Check out South_African_Geodata

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