Add UInt8 classification

This adds a classification into UInt8 buckets because we don't need the full accuracy of Float.
This is a good compromise between flexibility and size of the output data.

Author: felixcremer

src/rqatrend.jl

@@ -48,10 +48,23 @@ rqatrend(xout, xin, thresh)
 Compute the RQA trend metric for the non-missing time steps of xin, and save it to xout. 
 `thresh` specifies the epsilon threshold of the Recurrence Plot computation
 """
-function rqatrend(pix_trend, pix, thresh=2)
-    pix_trend .= rqatrend_impl(pix; thresh)
+function rqatrend(pix_trend, pix, thresh=2, lowerbound=-5., upperbound=-0.5)
+    pix_trend .= classify_rqatrend(rqatrend_impl(pix; thresh); lowerbound, upperbound)
 end
 
+function classify_rqatrend(trend, lowerbound=Float32(-5.0), upperbound=Float32(-0.5))
+    ctrend = clamp(trend, lowerbound, upperbound)
+    rlength = upperbound - lowerbound
+    return round(UInt8, 255-((ctrend - lowerbound) / rlength) * 255)    
+end
+
+@testitem "classify_rqatrend" begin
+    @test RQADeforestation.classify_rqatrend(-4.999) === UInt8(255)
+    @test RQADeforestation.classify_rqatrend(1) === UInt8(0)
+    @test RQADeforestation.classify_rqatrend(-0.52) === UInt8(1)
+    @test RQADeforestation.classify_rqatrend(-6) === UInt8(255)
+    @test isempty( AllocCheck.check_allocs(RQADeforestation.classify_rqatrend, (Float32, Float32, Float32)))
+end
 
 function rqatrend_impl(data; thresh=2, border=10, theiler=1, metric=CheckedEuclidean())
     # simplified implementation of https://stats.stackexchange.com/a/370175 and https://github.com/joshday/OnlineStats.jl/blob/b89a99679b13e3047ff9c93a03c303c357931832/src/stats/linreg.jl