Length of an object in a 2D image

Hi,

I’m trying to train a model to measure the length of an object in a 2D image. The object could be in an unknown orientation but I’d like the length of one axis. I’ve done some reading, and it sounds like a decent architecture would be a U net (say pre-trained resnet101) followed by a fully connected layer then a layer with one output node.

Does that sound reasonable?

Thanks.