How to Use Image Guides in the Form

When collecting data in the field, it may be useful to have a visual guide as a reference to ensure that correct information is entered in the form. For example, when collecting information about trees, it may help to see a reference photo of the tree trunk to identify the type of tree correctly.

Example project available

Clone documentation/image_guide to explore this setup.

Data, layers, and attributes

In this scenario, we want to include a photo guide in the form so that users can compare the type of a tree trunk to a reference picture while collecting data in the field.

The Mergin Maps project contains:

• a survey layer (here: trunk_type.gpkg) with the form configured to display or hide the image guide
• a table (here: list.gpkg) that is used as a value relation in the survey layer's attributes form, so that users can choose a tree type from a drop-down menu
• a reference photo for each type of tree, stored in the Mergin Maps project folder and packaged with the project

The survey layer (here: trunk_type) has following fields:

• type to store a the tree type
• photos to store a photo of the surveyed tree
• display used to display or hide the image guide
• date to store the survey date
• image_guide_xy to display the reference image of the specific tree trunk type. There is a separate field for each type.

Attributes form configuration in QGIS

We use the Drag and Drop Designer option in the Attributes Form tab of Layer Properties to configure the form.

The image guide is set up as follows:

• The display field uses the checkbox widget with true and false values.

  The alias of the field is set to Show me photo guide.

  

• The tab named Photo guide is used to group all image_guide_xy fields.

  The tab uses conditional visibility so that the image guide is displayed only when display = 'true'

  

• The photo guide fields image_guide_xy use the Attachment widget with Relative paths.

  The Integrated Document Viewer is set to Image to display the picture in the form.

  The default values contain the name of the reference picture (such as scots_pine.png). This ensures that the image guide is present when a new feature is created.

  

Image guide in the mobile app

When the form is opened in the mobile app, the image guide can be easily displayed and hidden by toggling the Show me photo guide checkbox.