Author: Laurence D. Finston

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Last updated: August 7, 2007

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Introduction |

Intersections |

Pseudo-Paraboloid |

Standardizing |

Classifying Points with Respect to a Parabola |

Contact |

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2005.11.09.

I've now added the data type **parabola** to the 3DLDF language.
It corresponds to the type **class Parabola** in the C++ code.

The 3DLDF code for generating the following image is in prbla_00.ldf. TeX code for the including it is in prbla_00.txt.

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The 3DLDF code for generating the following image is in prbla_05.ldf. TeX code for the including it is in prbla_05.txt.

The intersection points of a parabola **p** and a line seqment
**l** such that **p** and **l** are coplanar.

The 3DLDF code for generating the following image is in prbla_12.ldf. TeX code for the including it is in prbla_12.txt.

The intersection points of a parabola **p** and two line seqments
**l** and **m**, such that **p** and
**l**, and **p** and **m** are non-coplanar.

The 3DLDF code for generating the following image can be found in prbla_11.ldf. TeX code for the including it can be found in prbla_11.txt.

The intersection points of a parabola and a plane.

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The following four images represent a paraboloid generated by rotating
a parabola about the x-axis. The circles parallel to the axis of the
parabola (the x-axis) are **paths** created by taking corresponding
**points** from the **parabola** each time it's rotated.

The 3DLDF code for generating these images is in prbla_01.ldf. TeX code for including it is in prbla_01.txt.

Parabola: | |

vertex at origin | |

parameter = 3cm | |

axis = positive x-axis | |

Focus: | |

position: (0, 10cm, -20cm) | |

direction: (0, 10cm, 100cm) | |

distance: 15cm | |

Parallel Projection, X-Y Plane

Parallel Projection, X-Z Plane

(Similar to the last one, isn't it?)

Parallel Projection, Z-Y Plane

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A **parabola** can be standardized or placed in
standard position, i.e., in the x-z plane, with its vertex
at the origin and its focus on the positive x-axis.

This is done using the `standardize`

operator, which
returns a `transform`

.
`standardize`

leaves the `parabola`

unchanged.
To actually put it into standard position, you must
multiply it by the `transform`

that was returned.

The following is the gist of the code for creating the following four images. The complete code can be found in prbla_06.ldf. TeX code for including them is in prbla_06.txt.

parabola p; set p with_parameter 3 with_extent 7; rotate p (75, 50); shift p (3.5, 8, -1.75); transform t; t := standardize p; p *= t;

Perspective Projection

Focus: | |

position: (-5cm, 10cm, -20cm) | |

direction: (-5, 10cm, 100cm) | |

distance: 15cm | |

Parallel Projection, X-Y Plane

Parallel Projection, X-Z Plane

Parallel Projection, Z-Y Plane

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`points`

can be classified according to their position with respect to a
`parabola`

by using the `location`

operator:

parabola q; set q with_parameter 3 with_extent 7; point p; p := (2, 3, 4.5); r := p location q;

`location`

returns one of the following numerical values:

0:
The `point`

lies on the segment of the parabola represented
by the `parabola`

.

1:
The `point`

lies on the parabola, but not the segment, represented
by the `parabola`

object.

2:
The `point`

lies in the region enclosed by the branches of the parabola and the
line connecting the end points of the segment.

3:
The `point`

lies between the branches of the parabola, but
outside the region enclosed by them and the line connecting the
end points of the segment.

-1:
The `point`

is
coplanar with the `parabola`

,
but does not lie on the curve or between the branches.

-2:
The `point`

is not coplanar with the `parabola`

.

-3:
The `parabola`

is not parabolic.

-4:
The `point`

is invalid.

-5:
Something has gone terribly wrong.

The complete 3DLDF code for generating the following image can be found in prbla_10.ldf. TeX code for including it can be found in prbla_10.txt.

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