No record of the particulars of the construction of the ita_idx
shapefile.  Think maybe Bonnie did this one, in any case it is known
that she added flightline direction manually to the version of this
index that was used for orthorectification purposes.

itasca.txt came after-the-fact from GLAS, when we had asked for 2002
altitude values they sent itasca along as well.  That file appears to
contain plane orientation info in the COG field.