new landsat mask functions for landsat 4-7

[mateuszrydzik]

Recently I was trying to download older Landsat imagery (from 1993 to 2007) using rsi and get_landsat_imagery(). Landsat 5 and Landsat 7 images I downloaded had no values. I did some research and found that Landsat 4-5 and 7 use different QA pixel values than Landsat 8 and 9.

For clear lands with lows sets, QA pixel is 5440, and for clear water with lows sets = 5504.

As rsi::get_landsat_imagery() allows to select older datasets using platforms argument, additional mask functions can be useful.

More QA pixel values can be found in this document, on page 21

[mikemahoney218]

Thanks! This is a good idea to be built in, at least as its own standalone function (and maybe get_landsat_imagery() will look at the platforms argument to try and detect which one to use...). I won't have time to get to this soon, but seems like it should be easy to get into the next release!

[mikemahoney218]

The dev version of the package now has an argument, masked_bits, in the Landsat function that lets you control the bitmasks much more directly. I'm leaving this open because it'd be nice to provide a function that fills in the right bits by default, but, this might make things easier.