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Displaying the detected objects

In this part we're going to display the detected objects on the dashboard in two different ways.

First we will display an annotated version of the captured image with all of the objects highlighted. We will then add a table to the dashboard that lists them out.

Displaying an annotated image

The tf coco ssd node has an option to output an annotated version of the image with all of the detected objects highlighted. The image is set on the msg.image message property.

  1. Edit the tf node and configure the "Passthru" field to Annotated Image

  2. Add a Change node, wired to the output of the tf node and configure it to move msg.image to msg.payload.

  3. Wire the Change node to the input of the WebCam node.

  4. Click the Deploy button to save your changes.

Laying out flows

With this latest addition, you can see we now have wires crossing each other and looping back on themselves. As flows evolve, their wiring can become quite complex. It is always worth spending some time trying to find a layout that remains 'readable'.

There is a Flow Developer guide in the Node-RED documenation that provides a number of tips on how to layout flows.

Now when you take an image on the dashboard, you should see the annotated version of the image.

Adding a table of objects

Install the module node-red-node-ui-table using the Manage Palette option in the editor, or be running the following command in ~/.node-red:

npm install node-red-node-ui-table

This adds the ui_table node to the palette which can be used to display tabular data.

  1. In the Dashboard sidebar of the Node-RED editor, hover over the AI Photo Booth tab and click the + group button.
  2. Edit the new group and set its properties:
    • Set the name to 'Objects'
    • Set the width to 6 by clicking the button and dragging the box out to 6 units wide.
    • Untick the 'Display group name' option

  3. Add a new ui_table node from the "dashboard" section of the palette into your workspace. Edit its properties as follows:

    • Add it to the 'Objects' group
    • Set its size to 6x8
    • Add two columns by clicking the + add button at the bottom. Configure them as:
      • Property: class, Title: Object Type
      • Property: score, Title: Score, Format: Progress (0-100)

  4. Add a Change node to the workspace. Configure it to set msg.payload to the expression $append([],payload.{"class":class,"score":score*100,"bbox":bbox})

    Note

    Make sure you select the expression type for the to field of the Change node. This uses the JSONata expression language.

  5. Create the following wires between nodes:

    • wire the output of the tf node to the Change node.
    • wire the output of the Change node to the Table node
  6. Click the Deploy button to save your changes.

Now when you capture an image on the dashboard, the table should list the detected objects.

Side Quest - Star Ratings

The JSONata expression used in the Change node mapped the score property of each detected object from its original 0-1 range to the 0-100 range expected by the ui_table node's "Progress" column type.

The table supports a number of other formats of displaying numeric values. For example, it can map a number in the 0-100 range to a traffic light colour. It can also display a value in the range 0-5 as a number of stars.

Edit the table node to display the score using the star format. See if you can modify the expression in the Change node to map the original score to the required 0-5 range.

Side Quest - Clear the table

With the current dashboard, when an image is captured it gets displayed in place of the live web cam view until the clear button is clicked.

However clicking the button does not clear the table we've just added.

Using what you've learnt so far, build a flow between the Clear button and the table node that will clear the table when the button is clicked.

Hint: think about what payload must be passed to the table in order to clear it.

Next Steps

Now that we have an application, let's set up and run it on a Nvidia Jetson Nano. Proceed to the next Jetson Setup section.