Add Exp inverse functions of Log

Signed-off-by: Jason T. Brown <jason@astraea.earth>

Author: vpipkt

core/src/main/scala/astraea/spark/rasterframes/RasterFunctions.scala

@@ -328,4 +328,20 @@ trait RasterFunctions {
   def log1p(tileCol: Column): TypedColumn[Any, Tile] =
       Log1p(tileCol)
 
+  /** Exponential of cell values */
+  def exp(tileCol: Column): TypedColumn[Any, Tile] =
+    Exp(tileCol)
+
+  /** Ten to the power of cell values */
+  def exp10(tileCol: Column): TypedColumn[Any, Tile] =
+    Exp10(tileCol)
+
+  /** Two to the power of cell values */
+  def exp2(tileCol: Column): TypedColumn[Any, Tile] =
+    Exp2(tileCol)
+
+  /** Exponential of cell values, less one*/
+  def expm1(tileCol: Column): TypedColumn[Any, Tile] =
+    ExpM1(tileCol)
+
 }

core/src/main/scala/astraea/spark/rasterframes/expressions/package.scala

@@ -82,6 +82,10 @@ package object expressions {
     registry.registerExpression[Log10]("rf_log10")
     registry.registerExpression[Log2]("rf_log2")
     registry.registerExpression[Log1p]("rf_log1p")
+    registry.registerExpression[Exp]("rf_exp")
+    registry.registerExpression[Exp10]("rf_exp10")
+    registry.registerExpression[Exp2]("rf_exp2")
+    registry.registerExpression[ExpM1]("rf_expm1")
     registry.registerExpression[TileToArrayDouble]("rf_tile_to_array_double")
     registry.registerExpression[TileToArrayInt]("rf_tile_to_array_int")
     registry.registerExpression[DataCells]("rf_data_cells")

core/src/test/scala/astraea/spark/rasterframes/RasterFunctionsSpec.scala

@@ -607,5 +607,56 @@ class RasterFunctionsSpec extends FunSpec
       assert(df_0.select(log10(local_subtract($"tile", lit(0.01)))).as[ProjectedRasterTile].first().isNoDataTile)
 
     }
+
+    it("should take exponential") {
+      val df = Seq(six).toDF("tile")
+
+      // exp inverses log
+      assertEqual(
+        df.select(exp(log($"tile"))).as[ProjectedRasterTile].first(),
+        six
+      )
+
+      // base 2
+      assertEqual(
+        df.select(exp2(log2($"tile"))).as[ProjectedRasterTile].first(),
+        six)
+
+      // base 10
+      assertEqual(
+        df.select(exp10(log10($"tile"))).as[ProjectedRasterTile].first(),
+        six)
+
+      // plus/minus 1
+      assertEqual(
+        df.select(expm1(log1p($"tile"))).as[ProjectedRasterTile].first(),
+        six)
+
+      // SQL
+      assertEqual(
+        df.selectExpr("rf_exp(rf_log(tile))").as[ProjectedRasterTile].first(),
+        six)
+
+      // SQL base 10
+      assertEqual(
+        df.selectExpr("rf_exp10(rf_log10(tile))").as[ProjectedRasterTile].first(),
+        six)
+
+      // SQL base 2
+      assertEqual(
+        df.selectExpr("rf_exp2(rf_log2(tile))").as[ProjectedRasterTile].first(),
+        six)
+
+      // SQL expm1
+      assertEqual(
+        df.selectExpr("rf_expm1(rf_log1p(tile))").as[ProjectedRasterTile].first(),
+        six)
+
+      checkDocs("rf_exp")
+      checkDocs("rf_exp10")
+      checkDocs("rf_exp2")
+      checkDocs("rf_expm1")
+
+    }
   }
 }

pyrasterframes/python/pyrasterframes/rasterfunctions.py

@@ -239,7 +239,11 @@ def _(data_tile, mask_tile, mask_value):
     'log': 'Performs cell-wise natural logarithm',
     'log10': 'Performs cell-wise logartithm with base 10',
     'log2': 'Performs cell-wise logartithm with base 2',
-    'log1p': 'Performs natural logarithm of cell values plus one'
+    'log1p': 'Performs natural logarithm of cell values plus one',
+    'exp': 'Performs cell-wise exponential',
+    'exp2': 'Compute 2 to the power of cell values',
+    'exp10': 'Compute 10 to the power of cell values',
+    'exp1m': 'Performs cell-wise exponential, then subtract one',
 
     # ------- JTS functions -------
     # spatial constructors