How To Draw A Pepper With Contour Lines

This tutorial will discuss how to create contour lines in QGIS. Just earlier nosotros are discussing about cartoon contour lines in QGIS, permit'south commencement talking a little bit about the concept of profile line, what contour line definition is, profile lines characteristics and and how the method in drawing profile line . In the last section nosotros will come across how to create contour lines from points and besides from DEM in QGIS. For this tutorial I am using QGIS 3.0.

What is Contour Line?

Contour is a height isoline. Then what is an isoline? Isoline is a line on a map with a constant value. Therefore the profile definition is a line which has a constant top along the line. There are some characteristics of contour line such equally profile interval, contour elevation and distance between contour lines. If we meet a profile map we establish many lines on it. Those lines are never crossing to each other and each line has a unique elevation value that define its elevation on the map. Profile interval defines height interval between the line. For example if a profile map has 5 m interval contour, information technology ways the height different between the next contour line is 5 one thousand. If we know the distance between contour lines then we can summate the slope. The rule of thumb in defining contour interval is one/2000 ten map scale.

How to Draw Contour Lines

The bones method in drawing contours line is interpolation from a point dataset. The simplest interpolation method is linear interpolation which is oft used in drawing contours lines manually. In drawing a contour line with linear interpolation, at least three steps need to be done:

Connecting each point to form a TIN (Triangular Irregular Network) structure.
Do interpolation for each line in the Tin can.
Connecting the interpolation betoken with the same elevation.

Figure one shows pace by step approach in drawing contour line from connecting each point to form TIN, practise interpolation along the Tin can line and drawing contour line past connecting the same summit of interpolation points.

Figure 1. Profile line drawing

We already got some bones concepts about contour line. Now let'southward move to technical part how to create contour lines with QGIS. Firstly we volition see how to create profile line from a set of height points.

Create Contours from Points

To create contour lines from points, we are using Contour plugin. As usual we can become the plugin from Plugins carte du jour >> Manage and install plugins. In the search option type "Contour". You will run into the Contour plugin appears as in figure two. Check it and Install the plugin if yous don't have it in your QGIS 3.

Figure ii. Installing Contour Plugin

Now, let'due south make contour lines from points dataset with the following steps:

1. Add the points into QGIS map canvas equally in figure3.

Figure 3. Points dataset

ii. Open the Contour plugin past clicking the icon. The profile plugin window will appear every bit in figure 4.
3. Select the point's layer name and the tiptop data field. In the contouring menu, we can cull to create profile line, filled profile or both. Side by side, we have to define the number of contour lines. We can set any number, but I suggest the number of contour line follows the dominion of thumb equally mentioned higher up. For example if we desire to make a contour map in 100.000 scale, and so the contour interval will be 1/2000 10 100.000 = 50 grand. Then the number of contour line will be: maximum elevation/contour interval. 3554/fifty=71 lines. When nosotros gear up the calculated number, the profile interval tin can be seen in the right listing. Nosotros can tweak the number if the interval is not correct. That's why I change the number to 72. Moreover the interval can exist edited manually by double click the interval number.
4. Next we can specify the output name. The output will be written to retentiveness, so we need to consign to it to a GIS file to keep it permanently.
5. In the side by side setting we can specify the precision and unit for the profile label. Furthermore the color graduation for the contour lines can be changed past selecting a color ramp for the output profile lines.
6. When terminate click the Add button. The result can be seen in the QGIS map canvas without endmost the contour plugin window, therefore we tin switch back to change a parameter if the effect not looks as we want. Figure v shows the result of contour lines.

Figure 4. Contour plugin window

Figure five. Contour lines result from points

Create Contours from DEM

In this function we volition create contour lines from DEM. To create contour lines from DEM we tin can use the Contour tool in the Raster menu >> Extraction >> Contour. See effigy 6.

Figure 6. Contour tool

To create the contour lines from DEM, tin be washed with several steps:

Figure seven. DEM data in QGIS map canvas

2. Open up the Contour tool. The contour tool window will appear as in figure 8.

Figure 8. Raster contour tool

3. Select the DEM data. So set the contour interval, in this instance I used 50 chiliad. In the Contours selection, nosotros can specify the contour output path or save it to temporary file.

iv. If all the settings already set. Click the Run in Groundwork button. The result will shown in QGIS map canvas as in figure ix.

Figure 9. Contour lines from DEM

Contour Smoothing

If we compare the result, the contour lines from DEM looks smoother than points. That'southward because the DEM contains more top information compare to points dataset. The DEM has information in each pixel, so it could consist of thousands pixel and elevation information. Just don't worry. Nosotros tin can make the contour line from points smoother using Smooth tool as follow:

one. In the processing toolbox blazon "polish". The smooth tool will appear under Vector Geometry, as in figure 10.

Figure ten. Vector geometry smooth tool

2. Open up the shine tool. Select the input contour layer. Set the number of iteration, offset and maximum angle to smooth. The explanation of each parameter can be seen in the help window on the correct. See figure 11.

Figure 11. Contour smoothing

three. If all the parameters accept been set. Click Run in Background button to start the smoothing process. Figure 12 shows the comparing of contour lines before and later smoothing.

Contour lines before and after smoothing

Figure 12. Profile lines before and after smoothing

That'south all the tutorial how to create contour lines in QGIS both from points and DEM. I hope information technology'southward useful. Please give annotate if y'all find some other tool in QGIS or any improvement in creating profile lines using QGIS software. Anyhow, in creating contour lines some tools are used every bit already explained. Information technology'southward improve to build a model for it which can automate all the tools and can exist used repeatedly. Check out this tutorial how to create a model architect in QGIS.

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