Terrain with different heights without using a heightmap image

Hello,
I’ve already made a third-person view, controls(WSAD), and movement animations DEMO (wait a couple of seconds for the model to load, haven’t added loading indicators yet)

Now it’s time to create the terrain.
I need a simple example of how to create a curved plane without using a heightmap image.

An example of what I need

Do you mind sharing an image so it’s more clear what you are looking for.

Added an image

When you say that, you mean you don’t want to load an external texture, right? Would it be okay for you if such a texture would be generated procedurally in your code?

Sorry if I confused you
Here’s an example of generating heights based on the darkness or lightness of a pixel in an image.
Is there a simple solution to create these heights without using an image, such as an array of coordinates?

Yes, one options is to create height data with a noise algorithm. Check out the following example (especially the usage of ImprovedNoise):

https://threejs.org/examples/webgl_geometry_terrain