Geological mapping using open

Transcription

1 Geological mapping using open source QGIS MOHSEN ALSHAGHDARI

2 Abstract Geological mapping is very important to display your field work in a map for geologist and others, many geologists face problems to make their field output in a geological map. I face that for long till I learn myself online through open QGIS source, and other software. QGIS is easy to understand and my goal here to provide an easy steps to perform geological map with QGIS and some software, which you can use it for improve you map technically. I provide geological lithology symbols and some features you can use it side by side with QGIS, such as CLINO (MIDLAND VALLY) application which is found in Google play store for smart phones, also (TCX CONVERTER) as it will help you to pick many location points in one minute and projected in map which you are going to achieve if you miss it in field. GEOLOGICAL MAPPING A geological map is a graphical presentation of geological observations and interpretations on a horizontal plane.1 A geological section is identical in nature to a map except that data are recorded and interpreted on a vertical rather than a horizontal surface. Maps and sections are essential tools in visualizing spatial, threedimensional, geological relationships. Geologists need a number of items for the field. A hammer (sometimes two) is essential and some chisels. Also essential are a compass, clinometer, pocket steel tape, and a hand lens, plus a map case, notebook, map scales, protractor, pencils and eraser, an acid bottle and a jack-knife. A camera is a must and a small pair of binoculars can be most useful at times, as is a GPS instrument if it can be afforded, To make a geological map you need a topographic base map (in our case we will use Google earth as source of our image and topographic map) on which to plot your geological observations in the field. You can use electronic tools to perform some stuffs relating in geology in field such as CLINO compass for smarts phone for expert geologist see down. You can export it from phone as excel and move which is used for MOVE software and other geological sketch.

3 Introduction QGIS Quantum GIS is an open source software to create, modify and analyze Geographic Information Systems developed by the Open Source Geospatial Foundation (OSGeo). Main feature is the possibility to work on geo-- spatial data and the associated attributes. Based on a modular design, many functions (called plug-- in) can be added to the basic software. Being an open source project, new and better plug-- ins are constantly developed and tested. Website -- Quantum GIS, which is often called QGIS, is an open source GIS desktop application. Comparing to ArcGIS, QGIS can be installed on various operating systems, such as Windows, Mac OS X, Linux (Ubuntu), and Unix, while ArcGIS only has Windows version. More importantly, QGIS is FREE and has many plugins, adding different functions. However, since QGIS mainly relies on community support and voluntary developers, it does not have abundant documents and sometimes is not intuitive to use. Hence, making maps in QGIS needs some explanation. The two major steps, browsing data and making maps, are divided into five parts shown in the following table No. Steps Difficulties 1 Load Geospatial Data Data formats into QGIS 2 Identify the features and attributes to present Layer order, feature selection, and (briefly) frequent-used 3 Define how to show the data projections Transparency (raster and vector), data classification, and layer file 4 Add maps components Geospatial data references 5 Export maps File formats

4 Geological mapping with QGIS After you install your QGIS from Website and it is ready to use just double click on QGIS, this page will appear 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. Here I will use just add raster layer from here look down

5 Then choose from your computer the image you already took it from Google earth for mapping, for example I am planning to perform geological map for my village area(haqel ALFARED, DAMT, NW YEMEN). Go to Google earth and save it from there to your computer.

6 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). When you browsing to choose image which you copy it from Google earth this window will appears, just tick on WGS84 After click on WGS84 your image this will appear

7 Then you have to relocate the image which you import for mapping by geo-references. Take at least four point to get good geo-referenced image. To georeference an image is to define where it sits in a particular space (or this case, a defined datum). Choose the Georeferencer tool from the Raster menu. This dialogues will appears, 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.

8 Add the same image by click on add raster, when you click anywhere in image box of datum dialogue will open and you just fill the longitude and latitude for this point. Take at least four point, better to georeference from the corners of image. The information of these points you should collected before while your geological trip for study area, or collect it from Google earth. 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.

9 From the Settings menu, choose Transformation Settings. 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. When you finish taking points, click on start Georeferences, this will appear as you successfully relocate and project your image. Congratulations, now your image ready for geological mapping and adding features. Just close QGIS now and open it again and use your geo-referenced image. When you leave mouse anywhere will show you the longitude and latitude directly.

10 What to do now to perform geological map: First of all the geological features will add as different type of shape layers, - Faults will be adding as line - Strata will add as polygons - Wells and others will add as point Now I will start to add shape layer as lines for faults by following these steps: Click on Layer create layer- new shape file layer as below. Then you will get this window which has three choices of shape file layer, for fault system you will tick on line as mentioned below, the name will be filled by you as fault or as features you study. Then click ok. Save the line project in specific folder

11 Then you will see your shape file layer on QGIS (layered panel window), right click on it and choose toggle edition as below:

12 Click on toggle editing; now you can draw your lines in faults area as you see above the lines by click on add features button which is located in tool bar as mentioned down by red line. When you finish drawing your lines just click on toggle editing again, save your shape file. Congratulation your faults shape layer file performed. For wells you will choose file shape layer as points and follow instruction as we did in fault system. Notice -From the New shape file Layer window, choose Point. -Choose the correct CRS. - Give the new layer at least one Attribute. -Save the Layer in a reasonable location -Make sure that the Digitizing toolbar is selected. -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 re done. Congratulation you perform wells shape file layer and the output as map below:

13 Repeat same instructions for strata and other features as rocks outcrops, rivers and lakes by choose new shape file layer as polygon. 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. - 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. - 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 maneuvered to better represent the underlying geology. - By doing this over the entire area you can create a polygon that is representative of this geology

14 Congratulations now your map ready for finalizing technically. - Adding lithology symbols - Add scale bar - Add some articulations - Add north logo direction Adding lithology symbols as the QGIS and most of mapping software lack of lithology mapping I add lithology symbols at me research gate page: Download free at: / freestuff / cartoscript When you download lithology symbols just add it for QGIS as raster as instructions below: Click on features you add to layers panel, for my area is sandstone, right click, then click on properties, as mentioned in next illustration.

15 When you click on properties this box will appear: Click on raster image fill to add lithology symbols from your file which you download from website. Choose the type of lithology symbol and add it to your map.

16 Then your shape file features will change to that symbol you add.

17 Print composer The Print Composer is accessed by using the Project Menu. - In the Composition tab, you can edit the size and shape of your background map - It can be used to add scale bar, legends and other visuals to a map for presenting and publishing maps. - Making good maps is often the easiest way to portray geological information, as well as make a convincing argument. For adding north and scale bar etc., you will go to new print composer under project as below illustration or you will do ( CTRL +P) THEN THIS EMPTY BOX WILL appear, name it as you want, then click ok, new box will display and empty In the Print Composer there are several fundamental tools which you need to be able to manipulate to create sensible maps Firstly the Add New Map tool, which allows you to draw a box that will visualize what, is currently displayed in your QGIS window.

18 From this windows you can add text, image, north logo, any logo related your work, scale bar. And the output will be fantastic and your job is performed. حقل Now you can see all your field work display in geological map as I achieved for my village (HAQEL ALFARED ; DOWN AS YOU SEE (الفارد You can perform separately your features as you can just tick only on what features and print it and add illustration as needed like these maps what I performed for my village (same map). See down - Wells and structural geology - The boundary between salinity water and fresh water - Perform geological column - Contour map

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21 IF YOU MISS TO TAKE THE LONGITUDE AND LATITUDE IN LOCATION. JUST DOWNLOAD TCX CONVERTER. - GO GOOGLE EARTH, - MAKE NEW PATH AND PASS THROUGH ALL AREA EVEN MORE 1000 POINT - SAVE YOUR PATH AS KML - IMPORT YOU FILE TO TCX CONVERTER AND UPDATE ALTITUDE - EXPORT AS LAS, EXCEL FILE.

22 Notes - Geologist should learn how to drive and swim - Always wear hard hat to avoid damage your head - Use proper tools for your job For contact and any question MOHSEN ALSHAGHDARI mhsenhm@gmail.com