QGIS for Geoscientists

Transcription

1 QGIS for Geoscientists Robin Armit, Tom Carmichael, Lachlan Grose Monash Structural Geophysics group 22 nd 26th February 2016

2 GIS A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present all types of spatial data. From tracking diseases to vectors to mineralisation. 2

3 GIS GIS 3-4D modelling External data analysis 3

4 GIS QGIS is a open source, GIS package that can is freely available for Windows, Mac, Linux, BSD and Android. As with ArcGIS, it allows you to capture, store, manipulate, manage, conduct analyses and visualise a wide array of Geographical data. QGIS Download for Windows (2.8) QGIS Download for Mac OS X (2.8) QGIS Download for Linux (2.8)

5 GIS QGIS has an active support community which have answers to a wide array of questions. QGIS Support for users QGIS Documentation QGIS Stackexchange Forum QGIS Known issues and bug tracking A QGIS FAQ for how to ask a QGIS question and increase your chances of getting a response! Practical 1

6 Modern Light Table 6

7 The interface 7

8 A quick note on coordinate systems The co-ordinate system you choose for a map (or an individual point) defines where it appears in your GIS project. Older maps often have different datum to what is the current norm. Australia has moved approximately 18 centimeters since the calculation of GDA 94, always keep this in mind and check your measurements and coordinate system! Lake Cethana - Tasmania Point in GDA 94/WGS 84 space Point in AGD 66/AGD 84 co-ordinate system

9 Setting the coordinate system in QGIS There are two common ways to set the coordinate system in QGIS, either select the CRS (Coordinate reference system) tab. Or, if you re importing grids which have already been correctly referenced, right click on them in the layers bar and select set project CRS from Layer.

10 More on coordinate systems You must make a choice of Datum and coordinate system for your project. Normally depends on scale and location of project. Making an error here can put your 100 of metres out to half the globe. Below is a brief summary of the Australian map grid systems. Spheroid Datum Projection WGS84 WGS84 World UTM (world) AMG66 ANS70 AGD66 UTM (local using zones) AMG84 ANS70 AGD84 UTM (local using zones) MGA94 GRS80 AFN / GDA94 UTM (local using zones)

11 Georeferencing an image To georeference an image is to define where it sits in a particular space (or this case, a defined datum). This is crucial for importing Raster images into your project and using them for interpretation and analyses of an area. The British library has georeferenced 1000s of maps from its archive so that they can be viewed in Google Maps as overlays to compare with modern maps. This is an image first created in 1857 for the British Hydrographic survey.

12 Georeferencing an image 1. Choose the Georeferencer tool from the Raster menu. Select Open Raster from the File menu. Input the correct Coordinate system (AGD 66/AMG zone 54) From the Settings menu, choose Transformation Settings. Add Control Points by making sure that Add Point is highlighted then select a point on the map where the coordinates are known. Input the required easting and northing. Repeat this step at least 3 times. Choose the transformation type: Linear, Resampling Method: Linear. Change the Target SRS to a more modern projection (WGS 84/Zone 54S). Give the file an appropriate title and location. Select Start Georeferencing.

13 Georeferencing an image Choose the Georeferencer tool from the Raster menu. 2. Select Open Raster from the File menu. 3. Input the correct Coordinate system (AGD 66/AMG zone 54) From the Settings menu, choose Transformation Settings. Add Control Points by making sure that Add Point is highlighted then select a point on the map where the coordinates are known. Input the required easting and northing. Repeat this step at least 3 times. Choose the transformation type: Linear, Resampling Method: Linear. Change the Target SRS to a more modern projection (WGS 84/Zone 54S). Give the file an appropriate title and location. Select Start Georeferencing.

14 Georeferencing an image Choose the Georeferencer tool from the Raster menu. Select Open Raster from the File menu. Input the correct Coordinate system (AGD 66/AMG zone 54) 4. Add Control Points by making sure that Add Point is highlighted then select a point on the map where the coordinates are known. Input the required easting and northing. 5. Repeat this step at least 3 times.

15 Georeferencing an image 6. From the Settings menu, choose Transformation Settings. 7. Choose the transformation type: Linear, Resampling Method: Linear. Change the Target SRS to a more modern projection (WGS 84/Zone 54S). Give the file an appropriate title and location. 8. Select Start Georeferencing.

16 Basemaps Setting the coordinate system in QGIS 16

17 Loading a layer (Raster or Vector) The majority of your GIS projects will be defined by layers made up of either Rasters or Vectors. A Raster is a spatial dataset that defines space as an array of equal sized cells arranged into rows and columns (e.g. Satellite imagery or referenced geological maps) A Vector dataset is one that is represented as geographic features, such as points, lines and polygons. Each layer type has its own drawbacks and advantages and are used to describe different data.

18 Loading a layer (Raster or Vector) Loading an existing layer is done through the Layer menu, either by choosing Add Raster Layer or Add Vector Layer depending the dataset you re importing. There are a range of other options depending on what data types you have available, but Vector and Raster are the most common.

19 Creating a new layer (Creating Points, Polylines and Polygons) To better interpret your data and to get a more detailed understanding, the creation of a set of different datasets is required. On the Ararat 50K mapsheet, there are many different features that can be observered, in its current state the image is a Raster but turning sections of it into a Vector can provide more insight. There are features on this map that can be turned into points, lines or polygons.

20 Creating a new layer (Creating Points, Polylines and Polygons) 1. From the Layer menu, select New Shapefile Layer. From the New Vector Layer window, choose Point. Choose the correct CRS. Give the new layer at least one Attribute. Save the Layer in a reasonable location.

21 Creating a new layer (Creating Points, Polylines and Polygons) From the Layer menu, select New Shapefile Layer. 2. From the New Vector Layer window, choose Point. 3. Choose the correct CRS. 4. Give the new layer at least one Attribute. 5. Save the Layer in a reasonable location.

22 Adding to a layer (Point) 1. Make sure that the Digitizing toolbar is selected. 2. The correct Layer needs to be highlighted (Points) From the Digitizing ribbon, select the Toggle Edits cursor. Select the Add Feature button. Select a point of interest, give it the Attributes that you previously assigned. Click Save Edits once you ve completed adding points.

23 Adding to a layer (Point) Make sure that the Digitizing toolbar is selected. The correct Layer needs to be highlighted (Points) 3. From the Digitizing ribbon, select the Toggle Edits cursor. 4. Select the Add Feature button. 5. Select a point of interest, give it the Attributes that you previously assigned. 6. Click Save Edits once you re done.

24 Polylines Digitizing polylines is done in the same way that the creation of points, except that the end result is defined by a line, instead of a single point. The can be used to represent a large amount of geological data that is defined as linear. It is extremely important to use the style tool to make sure that you can visualise what each of your line represents. This will be covered later in this course.

25 Polygons Layers that are created as Polygons are initially added in the same way that polylines and points are. Polygons are used to define enclosed 2D areas. It is defined by a set of (x,y) co-ordinate pairs.

26 Polygons Create an initial polygon by selecting four points on the map, the program will join these four points with straight lines. By using the Snapping Options from the Settings menu and choosing the tolerance as around 20 pixels, you can snap to a node from your polygon when you are close to it.

27 Polygons By adding extra nodes to a line, by double clicking on the edge of a polygon with the Node Tool selected. With the Node tool still selected, each of these individual nodes can be manoeuvred to better represent the underlying geology. By doing this over the entire area you can create a polygon that is representative of this geology

28 Importing Tables The data you initially collect in the field will unlikely be in a format that you can directly import into a GIS package. The easiest way to solve this is to convert a table (usually a.csv file) into something more workable. Using GIS it is possible to turn field data, into manipulable, useful, information

29 Importing a table 2. Select your text delimited file and fill in the data required. 1. Choose Delimited Text Layer from the Layer menu.

30 A quick word on tables It is vital that before you go out into the field, that you know what data you re going to collect and how your input table should be set up. What information do you need to record at each location? Do you have a comments section to record pertinent information? What coordinate system is my GPS in? Was my data input into my table correctly? (Have I qaqc d my data?) Are all my measurements in Strike and dip or dip and dip direction? Do my numbers make sense? Did I record them all in the same way? All of these questions (and more!) need to be dealt with before you try to import your data. Otherwise, any errors that you bring in will be involved in your interpretation.

31 Todays task Familiarisation with GIS Download and install QGIS Setup the plugins Import existing data stylise the data Draw onto your map Export as a PDF or Image file

32 Setting up the files Download KANMANTOO PRAC.ZIP Create the following directories GFG Day1 images shapefiles Unzip the files inside the kanmantoo into the images folder The otherfiles into the "shapefiles" folder Move all the map_extent files from images to shapefiles

33 Plugins Way to add extra features to the program QGIS plugin repository has about 500 plugins Or you could write your own For this course we need: Openlayers Autotrace Clipper Contour Generalizer Qgis2threejs

34 The plugin manager

35 Adding existing data

36 Organising your project Select all the images and right click group Select all shape files "map extent, geology of Kannmantoo, Cambrian geology of Kanmantoo" and group You can name these groups as you want

37 Stylising your shapefiles Find out the properties each shapefile has: Right click and open attribute table Work out the best one to colour them by... eg lith group Right click shapefile and open properties then click the style tab Column == the attribute to colour them by Select categorised Press classify

38 Creating a shapefile

39 Naming and saving your files Use a descriptive name not "shapefile" Try to avoid spaces Try to save them in the one place You can save multiple lines (form lines, faults etc) in the one shapefile no need for a shape file for each fault type!

40 Now setup the attributes Think about how you will classify a line e.g. type, age etc. Open up the attribute table and click the pen to make the shapefile editable. Add new column - select the appropriate type e.g. integer, double or text pay attention to the length and precision you need

41 Adding a feature Add a normal fault Add feature draw a line (doesn't need to be a fault) Add the relevent attributes SAVE

42 Stylising the fault line Open the shapefile properties and classify by your relevant column Double click the symbol for your "normal fault" Add another line Change to a marker line Change marker to an esri font that looks like a normal fault symbol Change offset so marker sits on the line

43 Try and make a sinistral and dextral symbol

44 You should be able to Import raster and vector files Stylise your vector files Create your own shapefile and assign attributes to draw structures Create a polygon shapefile for lithologies Now we will export a map

45 Additional toolbars Advanced editing and digitising - clipping, merging, tracing

46 Advanced editing and digitising - clipping, merging, tracing

47 Using the clipping tool Make two polygons share a border Select the polygon(s) you want to keep Vector clipper Shape to keep

48 Autotrace Alternative to using the clipping tool The AutoTrace plugin for QGIS allows for new polygons to be digitized based on the vertices of pre-existing features. To use the AutoTrace feature, the snapping options will need to be set that it is simple to clip a vertex. To use the AutoTrace tool, first Toggle Editing of a layer, then select the AutoTrace tool. When snapped to a new vertex, trace along features with the shift key Trace the longest distance around a polygon (between two vertices) with the ctrl+shift keys together. AutoTrace (Editing enabled)

49 Freehand drawing

50 Generaliser Select your shapefile that has the lines Open up generaliser

51 Print composer The print composer is a powerful way of exporting your map with grids, axis, labels etc.

52 Once it is open add your map

53 To change the settings of the map layout You can resize by dragging the corners View -- panels : make sure item properties is checked

54 To add grid lines Item properties grid and add a new grid.

55 To add labels

56 Adding an overview Add another map that is your "zoomed in" area Go to the main qgis window and select the area you want to zoom in on Go to your new map and set map canvas extent

57 Adding an overview box on the larger map Now select the original map

58 Changing the style of the overview outline

59 What's missing? Try adding a north arrow Scale bar Legend Export to a pdf/png/svg

60 Custom forms Select type you have used before Can increment with arrows Choose lithos from your lithology shapefile

61 Custom form for adding feature

62 Custom form for adding feature Create a category as a tab main Select main and transfer the attributes you want across using the > button

63 Changing the input of attributes Unique values editable gives you a drop down menu and you can add new fields.. Prevents typos Range for numerical data e.g. strike dip 0-90 Value relation to get attributes from another shapefile

64 Using data attributes One of the most powerful aspects of a GIS package is the ability to highlight aspects of a data set (be it a pointset, polygon or polyline) based on its attributes. Using data attributes can be used to represent properties about a data point too, such as rotation of a symbol to represent strike and dip. It is also possible to save data that has certain attributes as a new dataset by using a query to interrogate the data.

65 Assigning values to data based on a characteristic. Select Style from the sidebar and Categorized from the drop down menu. Select properties from the drop down menu of a layer (alternatively, double click)

66 Assigning values to data based on a characteristic. Choose a column to categorize by, then hit classify. By changing the symbol and colour ramp, you can create a map which is relevant to your data.

67 Strike and Dip Example of directional markers By choosing a rotation field in the Style menu of the Layer Properties menu, it is possible to rotate a symbol by a certain column. If you have dip direction as a column, you can rotate a symbol by this value. You can also scale the size of an observation by a column too. In QGIS you can create your own symbols, or download them.

68 Query Builder Open the General tab from the Layer Properties menu. Select Query Builder.

69 Query Builder There are several important features of the query builder which can make your life infinitely easier. If you select an option from the Fields sub-menu and then hit sample (or all) you get the values that are present in that field. By using the Operators we can build a query which will highlight certain things. If we re working with text then its easiest to choose a value from the Values because it needs to be exact. The IF and AND functions can help highlight areas which have more then one characteristic that we re interested in.

70 Query Builder By creating this query we can highlight only the features which are Silurian(Ludlow) and are Intrusives.

71 Query Builder By using Save As after right clicking on the layer that you ve built a query of will allow you to save a Shape File which only has the characteristics that you ve saved. There are more complicated Querys you can build, with more detailed explanations of each of the query functions in the QGIS wiki.