Re: PolygonIntersections, MeshRange: What do they do?
- To: mathgroup at smc.vnet.net
- Subject: [mg20653] Re: PolygonIntersections, MeshRange: What do they do?
- From: "Allan Hayes" <hay at haystack.demon.co.uk>
- Date: Sun, 7 Nov 1999 02:09:56 -0500
- References: <7vrcg0$2nq@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Ted, MeshRange: MeshRange is used for array-based graphics like SurfaceGraphics and ContourGraphics to specify the x and y ranges. With the following the default ranges are derived from the arraydimensions Show[SurfaceGraphics[{{1, 3, 4}, {2, 6, 1}, {4, 1, 7}, {5, 2, 4}}], Axes -> True] We can specify what we want with MeshRange: Show[%, MeshRange -> {{-9, -5}, {4, 9}}] If we plot with, for example, Plot3D[x+y, {x,-9, -5}, {y, 4,9}] then MeshRange -> {{-9, -5}, {4, 9}}] is automatically included in the SurfaceGraphics object generated. We can't mess things up Plot3D because MeshRange is not an option for it. PolygonIntersections: I must just take the book's statement that "PolygonIntersections -> False is useful in creating graphics objects which can be sent to certain external three dimensional rendering programs" Perhaps someone else will enlarge on this, but here are some experiments: gr = Show[Graphics3D[{Polygon[{{0, 0, 0}, {1, 1, 1}, {0, 1, 1}}], Polygon[{{0, 1, 1}, {0, 0, 1}, {1, 1, 0}}]}]] InputForm[gr] gr2 = Show[gr, PolygonIntersections -> False] Why not shown above? When we get the following Show[gr2] Looking at the input form we see that we have - the polygons have been split along the line of intersecton, - the colors are given explicitly using face form - polygon edges are suppresed with EdgeForm[] - - and are provided by explicit Line objects InputForm[gr2] We can show the splitting visually and see that the colour is not dependent on lighting Show[DeleteCases[gr2, _EdgeForm | _Line, Infinity], Lighting -> False] Allan --------------------- Allan Hayes Mathematica Training and Consulting Leicester UK www.haystack.demon.co.uk hay at haystack.demon.co.uk Voice: +44 (0)116 271 4198 Fax: +44 (0)870 164 0565 Ersek, Ted R <ErsekTR at navair.navy.mil> wrote in message news:7vrcg0$2nq at smc.vnet.net... > > When would I want to use the options below? I checked the documentation and > I still don't understand. > > In[1]:= > Options[Graphics3D, PolygonIntersections] > > Out[1]= > {PolygonIntersections -> True} > > ------------------- > > In[2]:= > Options[SurfaceGraphics, MeshRange] > > Out[2]= > {MeshRange -> Automatic} > > -------------------- > Regards, > Ted Ersek > > For Mathematica tips, tricks see > http://www.dot.net.au/~elisha/ersek/Tricks.html > > >