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+# t3d
+
+An implementation of 3D Turtle Graphics with Fluent API. When using the function, imagine that you are sitting on a turtle. You move or turn the turtle from the your viewpoint, not the viewpoint of OpenSCAD coordinates. 
+
+For more details, please see [3D turtle graphics](https://openhome.cc/eGossip/OpenSCAD/3DTurtleGraphics.html). 
+
+## Parameters
+
+- `t` : The data of a turtle. `t3d()` with no arguments will return a turtle with the point `[0, 0, 0]` and the unit vectors `[[1, 0, 0], [0, 1, 0], [0, 0, 1]]`.
+- `cmd` : It accepts a string or a list of commands. 
+    - Given a string: `"xturn"`, `"yturn"`, `"zturn"`, `"xforward"`, `"yforward"`, `"zforward"`, `"point"` or `"unit_vectors"`. If `"xturn"`, `"yturn"` or `"zturn"` is provided, the `angle` parameter is required. If `"xforward"`, `"yforward"` or `"zforward"` is provided, `leng` is required. `"point"` and `"unit_vectors"` are used to get respective data from a turtle.
+    - Given a list: `[[cmd1, value], [cmd2, value2], ...]`. For example, `[["xforward", 10], ["zturn", 120]]` will forward a turtle 10mm along the x axis and turn it 120 degrees around the z axis from your viewpoint. 
+- `point` : Set the position of a turtle.
+- `unit_vectors` : Set the unit vectors of a turtle.
+- `angle` : Set the angle of a turtle if `cmd` is not provided. Turn a turtle if `cmd` is `"turn"`. 
+- `leng` : Forward a turtle if `cmd` is `"forward"`.
+
+## Examples
+	    
+	include <turtle/t3d.scad>;
+	include <hull_polyline3d.scad>;
+	
+	leng = 10;
+	angle = 120;
+	thickness = 1;
+	
+	t = t3d(point = [0, 0, 0]);
+	t2 = t3d(t, "xforward", leng = leng);
+    t3 = t3d(t2, [
+        ["zturn", angle],
+        ["xforward", leng]
+    ]);
+    t4 = t3d(t3, [
+        ["zturn", angle],
+        ["xforward", leng]
+    ]);   
+    
+	hull_polyline3d(
+        [for(turtle = [t, t2, t3, t4]) t3d(turtle, "point")],
+	    thickness
+	);
+
+![t3d](images/lib2-t3d-1.JPG)
+	
+	include <line3d.scad>;
+	include <turtle/t3d.scad>;
+
+	module tree(t, leng, leng_scale1, leng_scale2, leng_limit, 
+				angleZ, angleX, width) {
+		if(leng > leng_limit) {
+			t2 = t3d(t, "xforward", leng = leng);
+
+			line3d(
+				t3d(t, "point"), t3d(t2, "point"), 
+				width);
+
+			tree(
+				t3d(t2, "zturn", angle = angleZ),
+				leng * leng_scale1, leng_scale1, leng_scale2, leng_limit, 
+				angleZ, angleX, 
+				width);
+
+			tree(
+				t3d(t2, "xturn", angle = angleX), 
+				leng * leng_scale2, leng_scale1, leng_scale2, leng_limit, 
+				angleZ, angleX, 
+				width);
+		}    
+	}
+
+	leng = 100;
+	leng_limit = 1;
+	leng_scale1 = 0.4;
+	leng_scale2 = 0.9;
+	angleZ = 60;
+	angleX = 135;
+	width = 2;
+
+	t = t3d(point = [0, 0, 0]);
+
+	tree(t, leng, leng_scale1, leng_scale2, leng_limit, 
+		angleZ, angleX, width);
+
+![t2d](images/lib2-t3d-2.JPG)