Transfering contours to the ground

Transfering contours to the ground

GIS, Surveying
In the previous article, we looked at how to generate contours at a desired interval from the DEM. In this section, we will go through the process of converting the generated contour lines into points that can then be transferred to the ground. In this article, we are using the Processing Toolbox, which comes with QGIS - and within processing, we will need to have SAGA GIS tools. Launch the Processing Toolbox Under the resulting dialog, search for the "Convert Lines to Points" algorithm. This is a SAGA algortithm that converts a line into a cluster of points. Select the contours layer and click on run. In our experience, the insert distance dialog did not have a meaningful impact - so we left its value at 1. The result is…
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Generating Contours from the DEM

Generating Contours from the DEM

GIS, Surveying
In our previous article we showed how we generated a digital elevation model (DEM) by interpolating spot heights in QGIS. In this article we will take you through the process of extracting contours using QGIS. This brings up the contour dialog as shown below In this dialog, we first select the raster file, which is the DEM we generated in the previous article. We then choose the name of the contour lines file. I like to include the interval name for easy identification later on. We also need to define the height interval between contours. In this example, I chose 1m but depending on the density of the data and the needs of the client, this could be 0.25m or 2.5 m or any other suitable value. When you click…
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Preparing the Digital Elevation Model

Preparing the Digital Elevation Model

GIS, Surveying
In our previous article, we outlined how we obtained spot heights using survey observations. In the next section, we will convert these spot heights to a digital elevation model using the Interpolation Plugin in QGIS. The first step is to confirm that the Interpolation plugin is installed in QGIS. If it does not exist, please install it. The next step is to open the Interpolation plugin from the Raster menu This brings up the interpolation dialog as shown below Under the vector layers drop down, select your CSV points layer. In the next dialog, select the attribute that holds the heights data. Ensure you add it to the dialog using the Add button. Select the interpolation method. I prefer the Inverse Distance Weighting (IDW). Set the cell sizes - in…
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Picking the Spot Heights

Picking the Spot Heights

Surveying
We occupied a control point that we had established in the middle of the farm and observed spot heights across the farm.We had challenges with bushes - so we advise that the exercise be undertaken after bush clearing has been done. We used a Nikon Nivo 1C total station for picking our details. We selected the spot heights to ensure that the areas with the most dramatic changes in topography were sampled more closely. We also ensured that the spot heights extended beyond the project area - this would be useful during interpolation to ensure that the entire mapping area was properly represented. The data was exported from the total station as a CSV file. We use QGIS for many of our operations. We created a new project and imported…
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The smart secret to keep your farm green during drought

The smart secret to keep your farm green during drought

Agricultural Technology, FrontPage, GIS, Mapping, Surveying
Times of drought can be very depressing. It is very hard for a farmer to deal with the death of their livestock because of hunger - or to look at bare soil where once was lush green vegetation. Smart farmers have discovered that keeping their grass greener for longer, helps them stretch their pasture into the next season. Their secret is ploughing along contours to ensure their soil absorbs a maximum amount of water. Contour farming is growing crops "on the level" across or perpendicular to a slope rather than up and down the slope. The rows running across the slope are designed to be as level as possible to facilitate tillage and planting operations on the contour. Our clients, who are farmers have found that ploughing along a contour…
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