Calculating area from a set of polylines ( coplanar)

Hi I am trying to capture the sq footage of my deck,
pool scan closed.3dm (1.1 MB)
pool scan open.3dm (1.3 MB)
but I cannot get the area command to work. I have closed the set of polylines. 2 files included. one closed and the original which is open. The open file has a small break near the long straight edge. Any help would be much appreciated. I added a 3rd file that should prove that the points on the lines are coplanar (CS z up)
pool with CS z up.3dm (1.3 MB)

You need first to join all the tiny curves using _join
Then combine the resulting polyline into one closed polyline using _curveboolean
your area should be:
1.33620685 (+/- 1e-09) square feet

how do you select them all after typing join? it let me box select one time but made a mess with lines everywhere but now it will no let me group select.

I got it thanks! join was the key but I had to close it off first by extending and edge.