![]() ![]() Add in your buffer distance and type the file path to your output and go!įigure 3.If this vector file has more than one shape in it you will need to select the line you wish to buffer prior to accessing the Geoprocessing Tools, then make sure you tick the “Use only selected features” box. Fill the dialogue box, being sure to direct QGIS to the correct input vector (i.e.To buffer: Vector>Geoprocessing Tools>Buffer(s).The size of the buffer will vary greatly depending on the scale of your mapping, complexity of the geology and density of surface measurements, but this part will be up to you and you may need to have a few attempts with different buffers before you get it just right. Measure an appropriate distance from your line that will allow the buffer to cover enough of your data for making a subset (e.g.This creates a polygon that will contain all the data you wish to subset and use in your cross section, thus excluding any irrelevant data that will prevent accurate section interpretation: ![]() To make a subset of the data I perform a line buffer. In most cases an even spread of surface data is preferable for geological maps, however, in some large mapping areas it is only practical to collect data along traverses, which are often pre-selected for section building anyway. The relevance of this section depends on the scale of your cross section and the distribution of surface data on your map. The location of Cross Section 1 is shown. Transparent digital geology with surface elevation data. Digital elevation model with contours – these data represent the surface that you will be plotting in your cross section Figure 2. If you have a large map area and a lot of structural measurements it will be important that you make a subset of these data otherwise you will get a section that is overpopulated with meaningless data plotted from outside the area of relevance.įigure 1.Bedding, foliations, faults, jointing) you wish to plot in your cross section. tiff, dem, grd, ers) and all the surface measurements (e.g. Produce a map including g eology, an elevation model (some form of raster that contains elevation data, (e.g.Be sure that your data is projected correctly otherwise you will encounter some major problems by the time you get to interpreting the cross section. Remember that maps are not always accurate and are themselves just a representation of the physical world. Map production is generally the first step a geoscientist will take to visualize the geological relationships that can be gleaned from the Earth’s surface. The following steps provide a basic reference for the creation of a cross section from within QGIS, one of the best open-sourced GIS packages around: 1. So it makes sense that we have good techniques for the computer-aided visualization and interpretation of cross-section data. Our propensity for operating within the digital realm means that the traditional methods and media for interpretation are obsolete. Hopefully these objects are not foreign to all of us, but certainly the contemporary geoscientist is familiar with the operation of GIS (Geographical Information Systems), which have greatly increased the efficiency with which we can visualize our data. Traditionally geologists used compasses and protractors while constructing cross sections by hand using media such as paper and mylar. This process represents a crucial brain exercise that not only tests a geologist’s skill, but also provides a clarified view of mapped geological relationships that can appear complex when interfering with topographical variations. The term cross section was developed from this process and describes a 2-dimensional interpretation of the geology constructed on a profile that has been extracted along a designated map-traverse. However, the first real step in model building (and a method that has been used since the birth of modern geology) relies on the correlation and projection of surface observations into the unknown using basic geological principles. The process of building 3-dimensional models has become increasingly automated through the development of specialized software, complex algorithms and a whole lot of arm-waving. It is also hugely beneficial when attempting to relate these features to more philosophical aspects such as Earth structure and geological evolution. Establishing this view is often a critical step towards understanding the geometries and relationships of subsurface features such as stratigraphy, faults, intrusions, caves and mineral deposits. These elevation models can be combined with geological maps to create a 3-dimensional view (or model) of the subsurface. Variations in this surface are depicted on maps as contoured elevation data or graduated raster images (with colour scales referenced to elevation magnitude). ![]() The Earth’s surface forms the interface between our human view of the world and the geology preserved beneath our feet. ![]()
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