Guide: 2D Landmark Data Acquisition

Step 1: Create a TPS File with tpsUtil

1. Select Operation: Choose “Build tps file from images”.
2. Input Directory: Browse and select the folder containing specimen images.
3. Output File: Name new .tps file and choose where to save it.
4. Create: Click “Setup” to verify the images are listed, then click “Create.” This file initializes all landmarks to zero for each image.

Step 2: Set Up tpsDig for Digitization

Open tpsDig to visually place landmarks on your specimens:

1. Input Source: Go to File > Input Source > File and select the .tps file you just created.
2. Set Scale (Optional): If your images include a ruler, use the “Set Scale” tool to drag a line across a known distance (e.g., 1cm) to calibrate measurements. If not, it defaults to 1mm.
3. Define Landmarks: It is critical to have a set of homologous points identified beforehand (e.g., tip of the dorsal cornua in cephalopharyngeal skeleton, costagial break in Phoridae wing) to ensure consistency across all specimens.

Step 3: Digitizing Landmarks

1. Activate Tool: Click the “Digitize Landmarks” icon (the crosshair/target icon).
2. Place Points: Click on the specimen in the exact order specified by your protocol⚠️. The software will automatically number the points.
3. Edit/Correct: If you misplace a point, switch to “Edit Mode” (arrow icon) to drag and reposition the landmark.
4. Navigate specimens: Use the “Next” arrow to move to the next image and repeat the process.

Step 4: Save and Verify Data

1. Save Data: Go to File > Save Data to update the .tps file with the X and Y coordinates of your landmarks.
2. Verify: You can open the .tps file in a text editor to see that the LM (landmark) value now correctly reflects the number of points captured for each specimen.

Link to Video: Landmarks acquisition in 2D using tpsDig

Link to Software: tpsUtil, tpsDig

Source: Morpho Prof YouTube Channel, SB Morphometrics