Crop Circles is a purely-client-side web app originally designed for accurately cropping circular center pivot irrigation fields from aerial imagery (collected with, for example, ærialbot), enabling the creation of a series of videos.

But nothing's keeping you from using it to crop circular objects from imagery-in-a-more-general-sense!

Among other adjectives, it is...

• simple – You can get started right away.
• highly configurable – Both the tool's behavior and the shape of the end results can be tweaked.
• fast – About as fast as an in-browser tool of its kind can reasonably be, anyway.
• small – Less than 2000 lines of vanilla JavaScript.
• robust – Your settings and selections are kept in local storage, and you can back up and restore them.
• well-documented – Read the next sentence for more info.

For more details, refer to the user's guide – you can access it through the "Learn more..." link within the web app.

No setup! It's a single HTML file with around 2000 lines of JavaScript code. (Yes, you don't even really need the dependencies in assets/ – text will look uglier, images in the user's guide will be missing, the sample image won't load, and zipping won't work without them, but the core functionality of the tool won't be affected.)

Just open it in any modern browser and get to work.

You may use this repository's contents under the terms of the MIT License, see LICENSE.

However, the subdirectory assets/ contains third-party software with its own licenses:

• Iosevka Aile, the typeface used throughout the interface, is licensed under the SIL Open Font License Version 1.1, see here.
• JSZip is used in accordance with its MIT License, see here.

The remaining files in assets/ have been downloaded from Google Maps with ærialbot (or, in some cases, derived from such downloads). Even though that's techically freebooting, I've written about why I think it's no big deal here. The filenames contain clues as to the locations depicted (except for the favicon, all are from the area shown in the sample image).

Further, the general layout has been adapted from Markdeep Diagram Drafting Board, a previous project of mine.

And finally, I've referenced the source code of Craciun Cezar's Simple Web Image Editor during the implementation of some key features – in fact, the commit history of this project contains some verbatim copies of portions of their code.