Qt 5.11 | Qt Data Visualization | Qt Quick 2 Surface Example

Qt Data Visualization | Commercial or GPLv3

# Qt Quick 2 Surface Example

Using Surface3D in a QML application.

The Qt Quick 2 surface example shows how to make a simple 3D surface plot using Surface3D with Qt Quick 2.

The focus in this example is on generating a surface graph from height data, so in this section we skip explaining the application creation. For more detailed QML example documentation, see Qt Quick 2 Scatter Example.

## Running the Example

To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.

## Adding Data to the Graph

This example shows two methods to set data to surface graph, using the HeightMapSurfaceDataProxy and ItemModelSurfaceDataProxy. First we go through setting the data using the height map specific data proxy. It is done with the code snippet below. The proxy itself is contained in a Surface3DSeries. Inside the HeightMapSurfaceDataProxy the `heightMapFile` specifies the image file containing the height data. The value properties in the proxy define the minimum and maximum values for surface area width and depth. This example shows the terrain around Tycho crater at imaginary position from 67 to 97 and from 30 to 60. Note that on the graph the scale on the Y dimension exaggerates the height.

      Surface3DSeries {
          id: heightSeries
          flatShadingEnabled: false
          drawMode: Surface3DSeries.DrawSurface
          visible: false

          HeightMapSurfaceDataProxy {
              heightMapFile: ":/heightmaps/image"
              // We don't want the default data values set by heightmap proxy.
              minZValue: 30
              maxZValue: 60
              minXValue: 67
              maxXValue: 97
          }

          onDrawModeChanged: checkState()
      }

The other method to set surface data used in this example is with model mapping. We do that by first defining a `ListModel` containing the data for the surface:

      ListModel {
          id: dataModel
          ListElement{ longitude: "0"; latitude: "0"; height: "124"; }
          ListElement{ longitude: "0"; latitude: "1"; height: "125"; }
          ListElement{ longitude: "0"; latitude: "2"; height: "124"; }
          ...

Then we set up a Surface3DSeries with a ItemModelSurfaceDataProxy:

      Surface3DSeries {
          id: surfaceSeries
          flatShadingEnabled: false
          drawMode: Surface3DSeries.DrawSurface

          ItemModelSurfaceDataProxy {
          ...

We add the actual data to the `itemModel` of the ItemModelSurfaceDataProxy. We also define the roles for columns, rows and values. In this example the row holds values for longitude, column for latitude and the value is for height.

      ...
      itemModel: surfaceData.model
      rowRole: "longitude"
      columnRole: "latitude"
      yPosRole: "height"
      }

## Showing Data

In the `main.qml`, we set up the Surface3D element to show the data and various UI elements to illustrate few interesting features.

First is the gradient to be used for the surface, which can be defined as seen in the following snippet. With the ColorGradient we set example colors from position 0.0 to 1.0.

      ColorGradient {
          id: surfaceGradient
          ColorGradientStop { position: 0.0; color: "darkslategray" }
          ColorGradientStop { id: middleGradient; position: 0.25; color: "peru" }
          ColorGradientStop { position: 1.0; color: "red" }
      }

This element is set into the `baseGradients` property in the `theme` used in Surface3D:

      theme: Theme3D {
          type: Theme3D.ThemeStoneMoss
          font.family: "STCaiyun"
          font.pointSize: 35
          colorStyle: Theme3D.ColorStyleRangeGradient
          baseGradients: [surfaceGradient]
      }

Other interesting features can be controlled with buttons.

The first button is to toggle on and off the surface grid, for which we use the following code:

      onClicked: {
          if (surfaceSeries.drawMode & Surface3DSeries.DrawWireframe) {
              surfaceSeries.drawMode &= ~Surface3DSeries.DrawWireframe;
              heightSeries.drawMode &= ~Surface3DSeries.DrawWireframe;
          } else {
              surfaceSeries.drawMode |= Surface3DSeries.DrawWireframe;
              heightSeries.drawMode |= Surface3DSeries.DrawWireframe;
          }
      }

Second button is for surface shading mode, which is controlled with this code:

      onClicked: {
          if (surfaceSeries.flatShadingEnabled === true) {
              surfaceSeries.flatShadingEnabled = false;
              heightSeries.flatShadingEnabled = false;
              text = "Show Flat"
          } else {
              surfaceSeries.flatShadingEnabled = true;
              heightSeries.flatShadingEnabled = true;
              text = "Show Smooth"
          }
      }

Third button is for series visibility, which is controlled with this code:

      onClicked: {
          if (surfaceSeries.drawMode & Surface3DSeries.DrawSurface) {
              surfaceSeries.drawMode &= ~Surface3DSeries.DrawSurface;
              heightSeries.drawMode &= ~Surface3DSeries.DrawSurface;
          } else {
              surfaceSeries.drawMode |= Surface3DSeries.DrawSurface;
              heightSeries.drawMode |= Surface3DSeries.DrawSurface;
          }
      }

Notice that the `drawMode` and `flatShadingEnable` properties are set for both series.

Fourth and fifth buttons are for controlling background features.

The last button is for switching between the two series, one of which uses HeightMapSurfaceDataProxy and the other one ItemModelSurfaceDataProxy. For this we use the following code:

      onClicked: {
          if (surfaceSeries.visible === false) {
              surfacePlot.axisY.max = 500.0
              surfaceSeries.visible = true
              heightSeries.visible = false
              middleGradient.position = 0.25
              text = "Switch to Height Map Series"
          } else {
              surfacePlot.axisY.max = 250.0
              surfaceSeries.visible = false
              heightSeries.visible = true
              middleGradient.position = 0.50
              text = "Switch to Item Model Series"
          }
      }

We also set the maximum value to 500 in model proxy to make the surface flatter and 250 on height map proxy to show exaggerated height. At the same time the middle color position on the gradient is modified to match the value range change.

## Example Contents

Files:

- qmlsurface/main.cpp
- qmlsurface/qml/qmlsurface/Data.qml
- qmlsurface/qml/qmlsurface/NewButton.qml
- qmlsurface/qml/qmlsurface/main.qml
- qmlsurface/qmlsurface.pro
- qmlsurface/qmlsurface.qrc

Images:

- qmlsurface/heightmap.png