Merge 776bd9b into 95511f6

.gitignore

@@ -16,3 +16,4 @@ deps/windows/usr/
 deps/windows/x64
 docs/build/
 test/kernels/
+deps/build.log

src/q.jl

@@ -0,0 +1,27 @@
+export q2m
+
+"""
+    q2m(q...)
+
+Find the rotation matrix corresponding to a specified unit quaternion.
+
+### Arguments ###
+
+- `q`: A unit quaternion (as any kind of iterable with four elements)
+
+### Output ###
+
+A rotation matrix corresponding to `q`.
+
+### References ###
+
+- [NAIF Documentation](https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/q2m_c.html)
+"""
+q2m(q...) = q2m(collect(q))
+
+function q2m(q)
+    length(q) != 4 && throw(ArgumentError("`q` needs to be an iterable with four elements."))    
+    r = Matrix{SpiceDouble}(undef, 3, 3)
+    ccall((:q2m_c, libcspice), Cvoid, (Ptr{SpiceDouble}, Ptr{SpiceDouble}), collect(q), r)
+    permutedims(r)
+end

test/q.jl

@@ -0,0 +1,20 @@
+@testset "Q" begin
+    let expected = [0.607843137254902 0.27450980392156854 0.7450980392156862;
+                0.6666666666666666 0.33333333333333326 -0.6666666666666666;
+                -0.43137254901960775 0.9019607843137255 0.019607843137254832]
+        actual = q2m(0.5, 0.4, 0.3, 0.1)
+        @testset for i in eachindex(actual, expected)
+            @test actual[i] ≈ expected[i]
+        end
+        q = [0.5, 0.4, 0.3, 0.1]
+        actual = q2m(q)
+        @testset for i in eachindex(actual, expected)
+            @test actual[i] ≈ expected[i]
+        end
+        q = (0.5, 0.4, 0.3, 0.1)
+        actual = q2m(q)
+        @testset for i in eachindex(actual, expected)
+            @test actual[i] ≈ expected[i]
+        end
+    end
+end