Difference between revisions of "Documentation:Tutorial Section 4"

Latest revision as of 14:28, 16 December 2016

This document is protected, so submissions, corrections and discussions should be held on this documents talk page.

Questions and Tips

Note: This section used to contain answers to frequently asked questions about POV-Ray as well as many useful tips not covered in other parts of this documentation. You should now refer to the online version of the POV-Ray Questions and Tips

The Camera-setup

Appendices

This document is protected, so submissions, corrections and discussions should be held on this documents talk page.

Difference between revisions of "Documentation:Tutorial Section 4"

Latest revision as of 14:28, 16 December 2016

Questions and Tips

Navigation menu

Search

@@ Line 8: / Line 8: @@
 <!--</wikitalk>--->
 ===Questions and Tips===
+{{#indexentry:Questions and Tips}}
+{{#indexentry:VFAQ}}
+{{#indexentry:FAQ}}
 <!--<sectiondesc desc=<"tutorial questions and tips">--->
-<!--<indexentry primary "Questions and Tips" "VFAQ" "FAQ">--->
+<p class="Note">
-<p>
+<strong>Note:</strong> This section used to contain answers to frequently asked questions about POV-Ray as well as many useful tips not covered in other parts of this documentation. You should now refer to the online version of the POV-Ray [http://wiki.povray.org/content/Knowledgebase:POV-Ray_Questions_and_Tips Questions and Tips]</p>
-This section contains answers to frequently asked questions about
-POV-Ray as well as many useful tips not covered in other parts of this documentation.</p>
-<p>
-While it was current at the time that this POV-Ray documentation help file was created,
-it will almost certainly be out of date by the time you are reading this. So, if you
-do not find an answer to your question here, please check out the [http://www.povray.org/search/redirect?VFAQ|_new <span title="Opens A New Window!">current version</span>]
-on the internet.
-</p>
-<p>
-If you have some question not answered in this FAQ, do not be afraid to
-contact the [http://tag.povray.org/|_new <span title="Opens A New Window!">TAG</span>]
-or ask in the proper group of the [news://news.povray.org|_new <span title="Opens A New Window!">POV-Ray news-server</span>].
-</p>
-===Language Tips and tricks to achieve useful things===
-===How do I make a visible light source?===
-<p><em>&quot;How do I make a visible light source?&quot;</em> or: <em>&quot;Although I put the
-camera just in front of my light source, I cannot see anything. What am I
-doing wrong?&quot;</em>
-</p>
-<p>A light source in POV-Ray is only a concept. When you
-add a light source to the scene, you are actually saying to POV-Ray
-&quot;hey, there is light coming from this point&quot;. As the name says, it is a
-light <strong>source</strong>, not a physical light (like a light bulb or a
-bright spot like a star). POV-Ray does not add anything to that place
-where the light is coming, ie. there is nothing there, only empty
-space. It is just a kind of mathematical point POV-Ray uses to make
-shading calculations.
-</p>
-<p>To make the light source visible, you have
-to put something there. There is a <code>looks_like</code> keyword in the
-<code>light_source</code> block which allows to easily attach an object to the
-light source. This object implicitly does not cast any shadows.  You
-can make something like this:
-<pre>
-light_source
-{ &lt;0,0,0&gt; color 1
-  looks_like
-  { sphere
-    { &lt;0,0,0&gt;,0.1
-      color { rgb 1 }
-      finish { ambient 1 }
-    }
-  }
-  translate &lt;10,20,30&gt;
-}
-</pre>
-</p>
-<p>It is a good idea to define both things, the light source and the looks_like
-object, at the origin, and then translate them to their right place.
-</p>
-<p>Note also the '<code>finish { ambient 1 }</code>' which makes the sphere
-to apparently glow (see also the next question).
-</p>
-<p>You can also get visible light sources using other techniques: Media,
-lens flare (available as 3rd party include file), glow patch, etc.</p>
-===How do I make bright objects?===
-<p><em>&quot;How do I make bright objects, which look like they are emitting light?&quot;
-</em>
-</p>
-<p>There is a simple trick to achieve this: Set the ambient value of the object
-to 1 or higher. This makes POV-Ray to add a very bright illumination value to
-the object so the color of the object is in practice taken as is, without
-darkening it due to shadows and shading. This results in an object which seems
-to glow light by itself even if it is in full darkness (useful to make visible
-light sources, or small lights like leds which do not cast any considerable
-light to their surroundings but can be easily seen even in the darkness).
-</p>
-<p>A more sophisticated method would be using an emitting media
-inside the object (and making the object itself transparent or
-semi-transparent).</p>
-===How do I move the camera in a circular path?===
-<p><em>&quot;How do I move the camera in a circular path while looking at the origin?&quot;
-</em>
-</p>
-<p>There are two ways to make this: The easy (and limited) way, and the more
-mathematical way.
-</p>
-<p>The easy way:
-<pre>
-camera
-{ location &lt;0,0,-10&gt;
-  look_at 0
-  rotate &lt;0,clock*360,0&gt;
-}
-</pre>
-</p>
-<p>This puts the camera at 10 units in the negative Z-axis and then rotates it
-around the Y-axis while looking at the origin (it makes a circle of radius
-).
-</p>
-<p>The mathematical way:
-<pre>
-camera
-{ location &lt;10*sin(2*pi*clock),0,-10*cos(2*pi*clock)&gt;
-  look_at 0
-}
-</pre>
-</p>
-<p>This makes exactly the same thing as the first code, but this way you
-can control more precisely the path of the camera. For example you can
-make the path elliptical instead of circular by changing the factors
-of the sine and the cosine (for example instead of 10 and 10 you can
-use 10 and 5 which makes an ellipse with the major radius 10 and minor
-radius 5).
-</p>
-<p>An easier way to do the above is to use the vrotate()
-function, which handles the sin() and cos() stuff for you, as well as
-allowing you to use more complex rotations.
-<pre>
-camera
-{ location vrotate(x*10, y*360*clock)
-  look_at 0
-}
-</pre>
-</p>
-<p>To get an ellipse with this method, you can just multiply the
-result from vrotate by a vector, scaling the resulting circle.  With
-the last two methods you can also control the look_at vector (if you
-do not want it looking just at the origin).
-</p>
-<p>You could also do more complex transformations combining translate,
-scale, rotate, and matrix transforms by replacing the vrotate() call
-with a call of the vtransform() function found in <code>functions.inc</code>
-(new in POV-Ray 3.5).</p>
-===How do I use an image to texture my object?===
-<p>The answer to this question can be easily found in the POV-Ray
-documentation, so I will just quote the syntax:
-<pre>
-pigment
-{ image_map
-  { gif &quot;image.gif&quot;
-    map_type 1
-  }
-}
-</pre>
-</p>
-<p>(Note that in order for the image to be aligned properly, either
-the object has to be located at the origin when applying the pigment
-or the pigment has to be transformed to align with the object. It is
-generally easiest to create the object at the origin, apply the
-texture, then move it to wherever you want it.)
-</p>
-<p>Substitute the keyword <code>gif</code> with the type of image you are
-using (if it is not a GIF): <code>tga, iff, ppm, pgm, png or sys</code>.
-</p>
-<p>A <code>map_type 0</code> gives the default planar mapping.<br>
-A <code>map_type 1</code> gives a spherical mapping (maps the image onto a
-sphere).<br>
-With <code>map_type 2</code> you get a cylindrical mapping (maps the image
-onto a cylinder).<br>
-Finally <code>map_type 5</code> is a torus or donut shaped mapping (maps the
-image onto a torus).
-</p>
-<p>See the documentation for more details.</p>
-===How can I generate a spline?===
-<p><em>&quot;How can I generate a spline, for example for a camera path for an animation?&quot;</em>
-</p>
-<p>POV-Ray 3.6 has a splines feature that allows you to create splines. This is
-covered in the documentation and there are demo files showing examples of
-use. There exist also third party include files for spline generation that
-have greater flexibility than the internal splines, for example
-the [http://www.geocities.com/ccolefax/spline/index.html|_new <span title="Opens A New Window!">spline macros by Chris Colefax</span>].
-</p>
-===How can I simulate motion blur?===
-<p>The official POV-Ray 3.6 does not support motion
-blur calculations, but there are some patched versions which do.
-</p>
-<p>You can also use other tools to make this. One way to simulate motion
-blur is calculating a small animation and then averaging the images together.
-This averaging of several images can be made with third party programs,
-such as the [http://iki.fi/warp/PovUtils/average/|_new <span title="Opens A New Window!">Targa Averager program</span>].
-</p>
-===How can I find the size of a text object?===
-<p><em>&quot;How can I find the size of a text object / center text / justify text?&quot;
-</em>
-</p>
-<p>You can use the <code>min_extent()</code> and
-<code>max_extent()</code> functions to get the
-corners of the bounding box of any object. While this is sometimes not
-the actual size of the object, for text objects this should be fairly
-accurate, enough to do alignment of the text object.</p>
-===How do I make extruded text?===
-<p>POV-Ray has true type font support built in that allows you to have 3D
-text in your scenes (see the documentation about the 'text' object for
-more details).
-</p>
-<p>There are also some outside utilities that will import true type fonts
-and allow user manipulation on the text. One of these programs
-is called Elefont.</p>
-===How do I make an object hollow?===
-<p>This question usually means &quot;how do I make a hollow object, like a
-waterglass, a jug, etc&quot;.
-</p>
-<p>Before answering that question, let me explain some things about how POV-Ray
-handles objects:
-</p>
-<p>Although the POV-Ray documentation talks about &quot;solid&quot; and &quot;hollow&quot; objects,
-that is not how it actually works. &quot;Solid&quot; and &quot;hollow&quot; are a bit misleading
-terms to describe the objects. You can also make an object &quot;hollow&quot; with
-that same keyword, but it is not that simple.
-</p>
-<p>Firstly: POV-Ray only handles surfaces, not solid 3D-objects.
-When you specify a sphere, it is actually just a spherical surface. It is only
-a surface and it is not filled by anything. This can easily be seen by
-putting the camera inside the sphere or by clipping a hole to one side of
-the sphere with the clipped_by keyword (so you can look inside).
-</p>
-<p>People often think that POV-Ray objects are solid, really 3D, with solid
-material filling the entire object because they make a 'difference' CSG
-object and it seems like the object is actually solid. What the 'difference'
-CSG actually does is to cut away a part of the object and <strong>add a new
-surface</strong> in the place of the hole, which completely covers the hole, so
-you cannot see inside the object (this new surface is actually the part of
-the second object which is &quot;inside&quot; the first object). Again, if you move
-the camera inside the object, you will see that actually it is hollow and
-the object is just a surface.
-</p>
-<p>So what is all this &quot;solid&quot; and &quot;hollow&quot; stuff the documentation talks of,
-and what is the &quot;hollow&quot; keyword used for?
-</p>
-<p>Although objects are actually surfaces, POV-Ray handles them as if they
-were solid. For example, fog and media do not go inside
-solid objects. If you put a glass sphere into the fog, you will see that
-there is no fog inside the sphere.
-</p>
-<p>If you add the &quot;hollow&quot; keyword to the object, POV-Ray will no longer handle
-it as solid, so fog and atmosphere will invade the inside of the object.
-This is the reason why POV-Ray issues a warning when you put the camera inside
-a non-hollow object (because, as it says, fog and other atmospheric effects
-may not work as you expected).
-</p>
-<p>If your scene does not use any atmospheric effect (fog or media) there
-is not any difference between a &quot;solid&quot; or &quot;hollow&quot; object.
-</p>
-<p>So all the objects in POV-Ray are hollow. But the surface of the objects is
-always infinitely thin, and there is only one surface. With real world hollow
-objects you have always two surfaces: an outer surface and an inner surface.
-</p>
-<p>Usually people refer to these kind of objects when they ask for hollow
-objects. This kind of objects are easily achieved with a 'difference' CSG
-operation, like this:
-<pre>
-// A simple water glass made with a difference:
-difference
-{ cone { &lt;0,0,0&gt;,1,&lt;0,5,0&gt;,1.2 }
-  cone { &lt;0,.1,0&gt;,.9,&lt;0,5.1,0&gt;,1.1 }
-  texture { Glass }
-}
-</pre>
-</p>
-<p>The first cone limits the outer surface of the glass and the second cone
-limits the inner surface.</p>
-===How can I fill a glass with water or other objects?===
-<p>As described in the &quot;hollow objects&quot; question above, hollow objects have
-always two surfaces: an outer surface and an inner surface. If we take the
-same example, a simple glass would be like:
-<pre>
-// A simple water glass made with a difference:
-#declare MyGlass=
-difference
-{ cone { &lt;0,0,0&gt;,1,&lt;0,5,0&gt;,1.2 }
-  cone { &lt;0,.1,0&gt;,.9,&lt;0,5.1,0&gt;,1.1 }
-  texture { Glass }
-}
-</pre>
-</p>
-<p>The first cone limits the outer surface of the glass and the second cone
-limits the inner surface.
-</p>
-<p>If we want to fill the glass with water, we have to make an object which
-coincides with the inner surface of the glass. Note that you have to avoid the
-<!--<linkto "black spots">coincident surfaces problem</linkto>--->[[Documentation:Tutorial Section 4.1#Why are there strange dark pixels or noise on my CSG object?|coincident surfaces problem]]
-so you should scale
-the &quot;water&quot; object just a little bit smaller than the inner surface of the
-glass. So we make something like this:
-<pre>
-#declare MyGlassWithWater=
-union
-{ object { MyGlass }
-  cone
-  { &lt;0,.1,0&gt;,.9,&lt;0,5.1,0&gt;,1.1
-    scale .999
-    texture { Water }
-  }
-}
-</pre>
-</p>
-<p>Now the glass is filled with water. But there is one problem: There is too
-much water. The glass should be filled only up to certain level, which should
-be definable. Well, this can be easily made with a CSG operation:
-<pre>
-#declare MyGlassWithWater=
-union
-{ object { MyGlass }
-  intersection
-  { cone { &lt;0,.1,0&gt;,.9,&lt;0,5.1,0&gt;,1.1 }
-    plane { y,4 }
-    scale .999
-    texture { Water }
-  }
-}
-</pre>
-</p>
-<p>Now the water level is at a height of 4 units.
-</p>
-===How can I bend a object?===
-<p>There is no direct support for bending in POV-Ray, but you can achieve acceptable
-bending with the [http://www.geocities.com/SiliconValley/Lakes/1434/bend.html|_new <span title="Opens A New Window!">Object Bender by Chris Colefax</span>].
-</p>
-<p>Some objects can be &quot;bent&quot; by just modelling it with other objects.
-For example a bent cylinder can be more easily (and accurately) achieved
-using the intersection of a torus and some limiting objects.
-</p>
-<p>It might be a bit strange why most renderers support bending but POV-Ray
-does not. To understand this one has to know how other renderers (the
-so-called &quot;scanline-renderers&quot; work):
-</p>
-<p>In the so-called &quot;scanline renders&quot; all objects are modelled with triangle
-meshes (or by primitives such as NURBS or bezier patches which can be very
-easily converted to triangles). The &quot;bending&quot; is, in fact, achieved by
-moving the vertices of the triangles.
-</p>
-<p>In this context the term &quot;bending&quot; is a bit misleading. Strictly speaking,
-bending a triangle mesh would also bend the triangles themselves, not only
-move their vertices. No renderer can do this. (It can be, however, simulated
-by splitting the triangles into smaller triangles, and so the &quot;bending&quot;
-effect is more accurate, although not yet perfect.) What these renderers do
-is not a true bending in the strict mathematical sense, but only an
-approximation achieved by moving the vertices of the triangles.
-</p>
-<p>This difference might sound irrelevant, as the result of this kind of
-&quot;fake&quot; bending usually looks as good as a true bending. However, it is not
-irrelevant from the point of view of POV-Ray. This is because POV-Ray does
-not represent the objects with triangles, but they are true mathematical
-surfaces. POV-Ray cannot &quot;fake&quot; a bending by moving vertices because there
-are no vertices to move. In practice bending (and other non-linear
-transformations) would require the calculation of the intersection of the
-object surface and a curve (instead of a straight line), which is pretty
-hard and many times analytically not possible.
-</p>
-<p>Note that isosurface objects can be modified with proper functions in
-order to achieve all kinds of transformations (linear and non-linear) and
-thus they are not really bound to this limitation. However, achieving the
-desired transformation needs some knowledge of mathematics.
-</p>
-<p>See also the
-<!--<linkto "variable ior">variable ior question</linkto>--->[[Documentation:Tutorial Section 4.1#Can I specify variable IOR for an object?|variable ior question]].
-</p>
-===Can I get non-grainy focal blur?===
-<p><em>&quot;The focal blur is very grainy. Can I get rid of the graininess?&quot;</em>
-</p>
-<p>Yes. Set <code>variance</code> to 0 (or to a very small value, like
-for example 1/100000) and choose a high enough
-<code>blur_samples</code>. The rendering will probably slow down quite a lot,
-but the result should be very good.</p>
-===Language Things that don't work as one expects===
-===Using several transparent objects makes them black?===
-<p><em>&quot;When I put several
-transparent objects one in front of another or inside another, POV-Ray
-calculates a few of them, but the rest are completely black, no matter
-what transparency values I give.&quot;</em>
-</p>
-<p>Short answer: Try increasing the <code>max_trace_level</code>
-value in the <code>global_settings</code> block (the default is 5).
-</p>
-<p>Long answer:
-</p>
-<p>Raytracing has a peculiar feature: It can calculate
-reflection and refraction. Each time a ray hits the surface of an
-object, the program looks if this surface is reflective and/or
-refractive. If so, it shoots another ray from this point to the
-appropriate direction.
-</p>
-<p>Now, imagine we have a glass sphere. Glass
-reflects and refracts, so when the ray hits the sphere, two additional
-rays are calculated, one outside the sphere (for the reflection) and
-one inside (for the refraction). Now the inside ray will hit the
-sphere again, so two new rays are calculated, and so on and so
-on...
-</p>
-<p>You can easily see that there must be a maximum number of
-reflections/refractions calculated, because otherwise POV-Ray would
-calculate that one pixel forever.
-</p>
-<p>This number can be set with the
-<code>max_trace_level</code> option in the <code>global_settings</code> block.
-The default value
-is 5, which is enough for most scenes. Sometimes it is not enough
-(specially when there are lots of semitransparent objects one over
-another) so you have to increase it.
-</p>
-<p>So try something like:
-<pre>
-global_settings
-{
-  max_trace_level 10
-}
-</pre>
-</p>
-===I'm getting color banding in the image===
-<p><em>&quot;When I make an image with POV-Ray, it seems to use just a few colors
-since I get color banding or concentric circles of colors or whatever where
-it should not. How can I make POV-Ray to use more colors?&quot;</em>
-</p>
-<p>POV-Ray always writes true color images (ie. with 16777216 colors, ie.
-shades of red, 256 shades of green and 256 shades of blue) (this can
-be changed when outputting to PNG or to B/W TGA but this is irrelevant when
-answering to this question).
-</p>
-<p>So POV-Ray is not guilty. It always uses the maximum color resolution
-available in the target image file format.
-</p>
-<p>This problem usually happens when you are using windows with 16-bit
-colors (ie. only 65536 colors, the so-called hicolor mode) and open
-the image created by POV-Ray with a program which does not dither the
-image. The image is still true color, but the program is unable to
-show all the colors, but shows only 65536 of them (dithering is a
-method that &quot;fakes&quot; more colors by mixing pixels of two adjacent
-colors to simulate the in-between colors).
-</p>
-<p>So the problem is not
-in POV-Ray, but in your image viewer program. Even if POV-Ray shows a
-poor image while rendering because you have a resolution with too few
-colors, the image file created will have full color range.
-</p>
 <!--<wikinav>--->
 <br>
@@ Line 524: / Line 20: @@
 [[Documentation:Tutorial Section 3.10#The Camera-setup|The Camera-setup]]</td>
 <td width=50% bgcolor=#EEEEEF align=right>
-[[Documentation:Tutorial Section 4.1#Rotation behaves very strangely|Rotation behaves very strangely]]</td></tr>
+[[Documentation:Tutorial Section 5#Appendices|Appendices]]</td></tr>
 </table>
 <!--</wikinav>--->