Skip fetching core kernel and gadget

When using ubuntu-image make new images, it will always download core kernel and gadget. How can i make image just using local snap?

this only works if you use the --extra-snaps argument (one per snap) to point directly to local files, but note that this marks the snaps un-upgradeable in the image, so it should only be used during development and testing …

Thanks. I have make it work with using downloaded core.snap…It’s diffcult to find how to download core.snap in the official document…