Scaling a Model in MeshLab

So far I’ve been using MeshLab for editing and measuring my photogrammetry models. The control models for measuring volume don’t have any georeferencing, so there’s no scale set when they’re exported. But I always have something visible in the model, of a known dimension, to scale the image later. Usually a straight line drawn on a piece of paper and stuck down.

import_model

Import the model you want to scale into MeshLab from the main tool bar. Once imported you can rotate the camera around the model with the left mouse button, and move the model by pressing the mouse wheel.

measure_tool

Use the measuring tool on the main tool bar to measure whatever you’ll be using to set the scale. This will give you a initial measurement for the known length that’s used to find the scaling factor, so record this number.

initial_scale

Deselect the measuring tool with the same button on the tool bar. Then you want to find the scaling function in the filters menu. It’s listed under “Normals, Curvatures, and Orientation” with the “Transform” options.

menu_scale

This opens a window with the parameters for the scale change. Before you put any numbers in here, you need to take your known length, and divide it by the initial length you measured on the model earlier. In my examples I had a known length of 5cm on my scale. So I divided this by the initial measurement, 0.791770, to get the scaling factor, 6.314965.

Put the scaling factor into any one of the x, y, or z axis. Also make sure the “Uniform scaling” option is checked, so the change applies to the other axis as well. Then apply the scale.

scale_options

After the change has been applied you may need to recenter the origin of the view on the model. To do this just double right click where you want the origin to be.

You can now check that the scale has been applied correctly with the measuring tool. It should show a value very close to the known length.

adjusted_scale

You’ll now probably want to export the scaled model so you don’t have to make this adjustment again in future. Use “Export Mesh As…” in the file menu to save the model without overriding the original. I usually add a note onto the end of the name to distinguish this model as having a scale.

menu_export

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