some errors

[ShiJianHan]

This is a good open source library, but I found some problems when using it.

1. can't find model touchdetect_resnet18_DigitSensor.pth

2. when I run contact_area.py，the code report errors：UnboundLocalError: local variable 'poly' referenced before assignment
   

3. when I run surface_3d.py， the code made some unknown mistakes. I debug it, and find the code will stop in networks.py——709 line
   

4. I don't know if there is something wrong with my use process. I think I need a more detailed instruction

[DavidYaonanZhu]

check #22 (comment)

[ShiJianHan]

check #22 (comment)

Thanks！