Re: [Visualpython-users] Confusion about rotating camera around an object.

[Bruce S. <Bru...@nc...>]

Here is a working program. The key point is that since you want to move 
the camera around the z axis, you need to make scene.up = (0,0,1), so 
that the "groundplane" is the ground. Also, you need to rotate by pi/2 
each time, not pi and 3*pi/2 the second and third times. There's no 
point in importing cylinder etc. separately, once you've said "from 
visual import *". Just for clarity I made the rotation gradual to make 
it easier to see what was happening.

from visual import *
scene.background = (.6,.6,.6)
scene.up = (0,0,1)
scene.forward = (0,.7,-.6)

groundframe = frame()
g = cylinder(frame = groundframe, radius =10 , red = 0, blue = 0,
             axis = (0,0,-.1), opacity= .5)
opacity = 0.5
shaftwidth = 0.2

axisframe = frame()
labelframe = frame()

xeaxis = arrow(frame = axisframe, shaftwidth = shaftwidth,
    axis=(10,0,0), color=color.red,opacity = opacity) #  xe red
xwaxis = arrow(frame = axisframe, shaftwidth = shaftwidth,
    axis=(-10,0,0), color=color.cyan,opacity = opacity) # xw  cyan
ynaxis = arrow(frame = axisframe, shaftwidth = shaftwidth,
    axis=(0,10,0), color=color.black,opacity = opacity) # yn black
ysaxis = arrow(frame = axisframe, shaftwidth = shaftwidth,
    axis=(0,-10,0), color=color.magenta,opacity = opacity) # ys magenta
zpaxis = arrow(frame = axisframe, axis=(0,0,4), 
color=color.yellow,opacity =
    opacity, shaftwidth = shaftwidth)    # zp yellow
zmaxis =arrow(frame = axisframe, axis=(0,0,-4), color=color.blue,opacity =
    opacity, shaftwidth = shaftwidth)    # zm blue

nlabel = label(frame = labelframe, pos = ynaxis.axis, text = 'N',
               opacity = opacity)
elabel = label(frame = labelframe, pos = xeaxis.axis, text = 'E',
               opacity = opacity)
wlabel = label(frame = labelframe, pos = xwaxis.axis, text = 'W',
               opacity = opacity)
slabel = label(frame = labelframe, pos = ysaxis.axis, text = 'S',
               opacity = opacity)

while True:
    scene.mouse.getclick()
    steps = 50
    for step in range(steps):
        rate(2*steps)
        scene.forward = rotate( scene.forward, axis = (0,0,-1), angle = 
pi/2/steps )


Chris Lyon wrote:
> Gives me a view over the south axis towards the centre of the frame.
> I want to rotate the camera so I can look over the E W and North axis 
> but maintain the overall 'display' If I had a box drawn at 0,0,0 I would 
> like to look at the four vertical faces inturn. by using the rotate command.
>
> I am trying to use rotate to enact 3 buttons which act out the following 
> three commands.
>
> scene.forward = rotate( scene.forward, axis = (0,0,-1), angle = pi/2 )
> scene.forward = rotate( scene.forward, axis = (0,0,-1), angle = pi )
> scene.forward = rotate( scene.forward, axis = (0,0,-1), angle = (3 *pi)/2 )
>
> i reckon I'm not really understanding up's effect on all this but i've 
> got to the randomly poking in numbers which isn't having much useful effect.
>
> I am trying to build an environment that i can rotate easily in 90 
> degree chunks at the press of a command button but maintain the overall 
> 'appearance'. In essence so I view the scene from a similar elevation 
> above the groundplane bu the position rotated appropriately round the 
> centre point.
>
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