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Man Pages


Manual Reference Pages  -  GLESPIRAL (3)

NAME

gleSpiral - Sweep an arbitrary contour along a helical path.

CONTENTS

Syntax
Arguments
Description
See Also
Author

SYNTAX


void gleSpiral (int ncp, gleDouble contour[][2], gleDouble cont_normal[][2], gleDouble up[3], gleDouble startRadius, /* spiral starts in x-y plane */ gleDouble drdTheta, /* change in radius per revolution */ gleDouble startZ, /* starting z value */ gleDouble dzdTheta, /* change in Z per revolution */ gleDouble startXform[2][3], /* starting contour affine xform */ gleDouble dXformdTheta[2][3], /* tangent change xform per revoln */ gleDouble startTheta, /* start angle in x-y plane */ gleDouble sweepTheta); /* degrees to spiral around */

ARGUMENTS

ncp number of contour points
contour 2D contour
cont_normal 2D contour normals
up up vector for contour
startRadius spiral starts in x-y plane
drdTheta change in radius per revolution
startZ starting z value
dzdTheta change in Z per revolution
startXform starting contour affine transformation
dXformdTheta tangent change xform per revolution
startTheta start angle in x-y plane
sweepTheta degrees to spiral around

DESCRIPTION

Sweep an arbitrary contour along a helical path.
The axis of the helix lies along the modeling coordinate z-axis.
An affine transform can be applied as the contour is swept. For most ordinary usage, the affines should be given as NULL.
The "startXform[][]" is an affine matrix applied to the contour to deform the contour. Thus, "startXform" of the form

| cos sin 0 |
| -sin cos 0 |
will rotate the contour (in the plane of the contour), while

| 1 0 tx |
| 0 1 ty |
will translate the contour, and

| sx 0 0 |
| 0 sy 0 |
scales along the two axes of the contour. In particular, note that

| 1 0 0 |
| 0 1 0 |
is the identity matrix.
The "dXformdTheta[][]" is a differential affine matrix that is integrated while the contour is extruded. Note that this affine matrix lives in the tangent space, and so it should have the form of a generator. Thus, dx/dt’s of the form

| 0 r 0 |
| -r 0 0 |
rotate the the contour as it is extruded (r == 0 implies no rotation, r == 2*PI implies that the contour is rotated once, etc.), while

| 0 0 tx |
| 0 0 ty |
translates the contour, and

| sx 0 0 |
| 0 sy 0 |
scales it. In particular, note that

| 0 0 0 |
| 0 0 0 |
is the identity matrix -- i.e. the derivatives are zero, and therefore the integral is a constant.

SEE ALSO

gleLathe

AUTHOR

Linas Vepstas (linas@fc.net)
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GLE GLESPIRAL (3GLE) 3.6

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