Suggestion/feature request: A ruler tool

[anttikos]

Measuring length of features is possible using annotations, but having a separate measurement tool would be very useful as well. The reasoning for this is, that the annotations are persistent, but some times the user might just want to know the length of the feature, without storing it as an annotation. Based on the measurement, the user could however start drawing the actual annotation, if they have permissions to do so.

One example of this could be that the image contains 5 different interesting areas, and user wants to annotate only one of them (the most interesting one). Decision of which one should be annotated could be partly decided on their physical dimensions (partly because of other properties). If user wants to measure length of all these features, they need to first annotate all of them using line tool, then select the best candidate, then delete the line tool annotations, and then start creating the final, more detailed annotation, that they want to save in the system. This seems like a lot of excess work for just getting the measurements, and there is a risk that user forgets to delete all the line annotations, polluting the annotation db.

Another use case would be that the user displaying the image does not necessarily have annotation rights, but is still interested knowing the measurement of different features of the image.