Photometrics method

[Jan 2020]

Introduction

This page describes a method to use LibreOffice Draw as an aid to measuring the real size of objects in a photograph. A summary of the method is as follows:

  1. Insert the photo into a LibreOffice Draw page
  2. Use the dimension tool to measure an object in the photo of known dimension (ideally a photo scale)
  3. Use the dimension tool to measure the object of interest in the picture
  4. Calculate the unknown actual dimension based on the measured known dimension

Preparation

The use of a photographic reference scale is recommended. These are available commercially, or you can print your own (also, see here for another printable version and tips on use). Purchase or make these, and practice taking photographs with them; take photos of objects of known dimensions and then make photo measurements to verify your technique.

Set up LibreOffice Draw as follows:

  • Under Tools/Options/LibreOffice Draw/General set the scale to 1:1
  • Use the Styles option to modify the arrow line settings:
    • Dimensioning : Set decimal places to 3
    • Line : Set color to light gray
    • Font effects : Set font color to black, outlined (this gives a black+white font which shows up well on all backgrounds)

I suggest setting the line and font colors to light gray as these provide good contrast for general use, but you may need to change these for some photos, depending on the background colors.

When using the dimensioning tool, I have found this technique effective : Use the page zoom option to make the object to be measured as large as possible in the frame. Set an initial dimension slightly smaller than the wanted dimension. Hold down the Altkey and adjust each end of the dimension line to the exact desired position (you may want to zoom in even more for the final adjustment).

To set up a page for measurement:

  • Open a page and select the Layout layer (make sure it is not locked)
  • Insert the desired photo and then lock the Layout layer
  • Select the Dimension Lines layer and then add your dimension lines as suggested above

Use the LibreOffice Calc spreadsheet (see resources below) to calculate actual dimensions.

Resources

Photographic reference scale:

Note : I laser printed this scale onto card stock, but I found this was a bit too flexible and had a tendency to curl. I suggest printing out the scales and gluing them to a rigid backing such as hardboard, plastic sheet, or similar. In any case, the finished product should be measured with an accurate ruler or digital caliper to verify that it is accurate.