area of flat polygon is not 0

[strk]

This may or may not be a bug, as a flat polygon is invalid, but at least for PostGIS the code implementing the signed area is documented (as comments in code) as expected to return 0, but it's not.
Code to check:

bin/geosop -area -a stdin --format txt <<EOF
POLYGON((                                   
  29.262792863298348 71.22115103790775,
  29.26598031986849  71.22202978558047,
  29.275379947735576 71.22044935739267,

  29.29461024331857  71.22741507590429,

  29.275379947735576 71.22044935739267,
  29.26598031986849  71.22202978558047,
  29.262792863298348 71.22115103790775
))
EOF

Outputs 1.69407e-21

[dr-jts]

That's Floating Point math for ya.