GIMP plugin

If you use an image editor like GIMP or Glimpse you can use Kotyle directly with a plugin to measure capacity and save the corresponding vector path of the vessel profile as GeoJSON data.

It is very easy to install and use the plugin. The README with installation instructions is here together with the plugin.

Both GIMP and Glimpse are freely distributed programs for image retouching and manipulation, available for all operating systems.

Installation

Installing this plug-in is very easy and requires copying one file in the right directory.

Open the Edit ‣ Preferences dialog from the main window.

The dialog has a long list of various preferences. The last item in the list should be “Folders” and among the sub-items there are “Plug-ins”. When you enter the preferences for plug-ins folders, you should find some paths listed and you can open the path in your user directory directly from the same dialog.

Copy the vector-to-geojson.py file in that directory. On Linux or MacOS, make sure the file is executable.

Restart The GIMP, and you will find the plug-in the Filters ‣ Kotyle menu.

Before you start: check image resolution

It is very important that you check the image resolution is the correct one, e.g. if you scanned a drawing at 300 dpi the image file must be set at the same resolution, otherwise all measurements will be wrong. This is fairly easy if you’re working with your own drawings, but it may require some work in case the drawings are from older digital archives.

You can set the image resolution from the Image ‣ Print size… menu item.

You will also need to make sure that the drawing is correcly rotated with respect to the geometric lines, that is the rotation axis must be a vertical straight line. Kotyle had a plugin for this but it became obsolete with GIMP 2.10 that includes the same functionality by default with the “Measure” tool and the associated “Straighten” function.

You can find the detailed manual on the GIMP website at <https://docs.gimp.org/2.10/en/gimp-tool-measure.html>_.

Vector paths in GIMP

Both plugins work with Paths in GIMP. Paths are separate from the raster layers and can be drawn on top of the existing layers.

There is a specific panel for Paths where they can be removed and renamed. Renaming is important here because we will need to be able to pick one or more paths and use them with Kotyle.

You can find the most recent documentation about paths in the GIMP Manual.

Drawing a vector path for a vessel profile

The Path tool allows you to create vector paths. You should either start from the vessel bottom (foot, base) or the top (rim) taking care to draw along the inner profile (assuming you want to calculate the volume of the vessel content).

Make sure you draw only one path for the profile. When you’re done, go the Paths panel in the main toolbox (close to the Layers panel) and rename your path to something useful, like Bowl Type 23.

Measuring vessel capacity

Go to the Plugins ‣ Kotyle menu (it should be close to the bottom of the menu) and click the Measure vessel capacity item.

A dialog will open, where you need to choose a few parameters:

  • the path (directory) where you want to save the file

  • the name of the file (default is profile.json but you want to choose a more sensible name if you have more than one profile) where to save the GeoJSON data of the vessel profile

  • the vector path you want to export – you will see that the drop-down list shows you the names of paths – you can choose only one path

  • title, description and author of the drawing, optional but useful

The computed capacity expressed in liters will be shown in a small window.

What to do with the GeoJSON?

In short, you are going to have one .json file for each profile you want to measure. These files are nothing special, you can open them with any text editor and look at their contents.

More details about the GeoJSON format are found in Describing the profile of a vessel in a digital format.

The Measure vessel capacity plugin will save your vessel profile in a file (e.g. named profile.json).

Kotyle has also a separate tool to calculate vessel volume from that file, called Μετρω, the Kotyle measurement tool. This tool is useful if you need to process many files at once.