Ubuntu-image: command not found

i am using Ubuntu 18.04.1 LTS \n \l, trying to build the sdcard image.

sudo ubuntu-image -c stable --image-size 700M --extra-snaps ubuntu-xenial/dragonboard-kernel_4.4.0-1103.108_arm64.snap --extra-snaps dragonboard-gadget/dragonboard_16.04-0.18_arm64.snap -o ubuntu-core-image-63b0-108.img 63b0.model

sudo: ubuntu-image: command not found

please suggest.

snapd is already the newest version (2.34.2+18.04).
snapcraft is already the newest version (2.43.1+18.04).


Have you installed the ubuntu-image?
If not sure, please try the command:

$ snap info ubuntu-image

If you didn’t, please install the ubuntu-image by command:

$ snap install ubuntu-image --classic

after installing ubuntu-image, able to create the image.