How to create a topographic profile with QGis 3.26 (Part 4)

Here’s a 5-chapter tutorial on the new QGis feature in version 3.26: elevation profiles.

Chapter 1: Profiles from vector layers

Chapter 2: Profiles from raster layers

Chapter 3: Profiles from point clouds (Lidar)

Chapter 4: Profiles layout

Chapter 5: Profiles in QField

Chapter 4: Profiles layout

The data required for this tutorial is available here.

Before moving on to page layout, there are two points we haven’t covered in the previous chapters.

The first concerns profiles based on contour lines. It may come as a surprise that the profile is truncated at the ends:

To understand what’s going on, we need to remember that the profile is constructed from the points of intersection of the profile line and the contour lines. To represent the profile as a line, we connect the points of intersection with straight lines, and to create a coloured surface, we construct a polygon by connecting the line of intersection points with the X axis. But as the profile line stops before reaching the next contour line, it is not possible to create an intersection point in empty space.

The second point we haven’t covered is

The measuring tool

l works like the measurement tool in the map window, except that here we have three values displayed:

  • Total length is the length of the line connecting the points
  • Distance is the length of the projection of the line connecting the points on the XY surface
  • Elevation is the projection of the line connecting the points on the Z axis.

Profile layout

Open the layout window: menu Project-> New layout
We add the Map Object to our layout:

To add the profile, go to the Add object -> Add elevation profile menu.

We get a blank profile:

In Object properties, there’s a “Copy from Profile” button that lets you import the profile from our QGis window.

Unlike the Map object, the Elevation Profile object lets you modify the profile’s appearance without having to return to the QGis window.

In particular, you can show or hide layers in the profile, and, most importantly, you can modify the profile tolerance band directly. These modifications are made on the layout profile, but are not transmitted to the profile in the main QGis window.

For the rest of the object property parameters, you can adapt the profile axes, as well as the other usual layout object parameters (position, size, rotation, etc.).

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