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I am modeling trains using Spline_Trans. Is there a way to average out the
points above each wheel set to get a position for the train so that it still
has the banking from Spline_Trans but shift over the side of the track so that
the wheels are above the tracks? Thanks.
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HelveticaFanatic <nomail@nomail> wrote:
> Is there a way to average out the points above each wheel
If you want to average a set of points, simply calculate their sum
and then divide by the amount of points?
--
- Warp
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Warp <war### [at] tag povrayorg> wrote:
> HelveticaFanatic <nomail@nomail> wrote:
> > Is there a way to average out the points above each wheel
>
> If you want to average a set of points, simply calculate their sum
> and then divide by the amount of points?
>
> --
> - Warp
I need to bank the train, too, and have it match the bank angle and slope of the
track. I just tried to average out two Spline_Trans transforms from 20
coordinates apart, but it didn't render (a syntax error).
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HelveticaFanatic <nomail@nomail> wrote:
> I need to bank the train, too, and have it match the bank angle and slope of the
> track. I just tried to average out two Spline_Trans transforms from 20
> coordinates apart, but it didn't render (a syntax error).
A syntax error does not mean it cannot be done. It simply means you didn't
write the correct syntax for it. Without seeing the code it's impossible to
say what is the cause of the error.
--
- Warp
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HelveticaFanatic wrote:
> I am modeling trains using Spline_Trans. Is there a way to average out the
> points above each wheel set to get a position for the train so that it still
> has the banking from Spline_Trans but shift over the side of the track so that
> the wheels are above the tracks? Thanks.
>
>
If I am understanding what you want, you can take points from along the
spline on either side of a given point, together with the root point you
can then use cross product (vcross(A,B) see the docs) to approximate a
normal which which would reflect the banking of the spline. You would
'normalize it of course and then multiply by the radius of your wheel to
get the level where the axle would be. If you don't quite understand
what I mean, I would suggest you research what cross product is and work
backward from there to a solution.
-Jim
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Jim Charter wrote:
> HelveticaFanatic wrote:
>
>> I am modeling trains using Spline_Trans. Is there a way to average out
>> the
>> points above each wheel set to get a position for the train so that it
>> still
>> has the banking from Spline_Trans but shift over the side of the track
>> so that
>> the wheels are above the tracks? Thanks.
>>
>>
> If I am understanding what you want, you can take points from along the
> spline on either side of a given point, together with the root point you
> can then use cross product (vcross(A,B) see the docs) to approximate a
> normal which which would reflect the banking of the spline. You would
> 'normalize it of course and then multiply by the radius of your wheel to
> get the level where the axle would be. If you don't quite understand
> what I mean, I would suggest you research what cross product is and work
> backward from there to a solution.
>
> -Jim
Actually I just realized how you can let POV do the work:
this would return the point one unit above the spline at the
current clock:
#declare Pt1 =
vtransform ( <0,1,0>, Spline_Trans(Spline, clock, y, .2, .5) );
these would return the points one unit each side of the spline at the
current clock:
#declare Pt2 =
vtransform ( <1,0,0>, Spline_Trans(Spline, clock, y, .2, .5) );
#declare Pt3 =
vtransform ( <-1,0,0>, Spline_Trans(Spline, clock, y, .2, .5) );
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Jim Charter <jrc### [at] msncom> wrote:
> HelveticaFanatic wrote:
> > I am modeling trains using Spline_Trans. Is there a way to average out the
> > points above each wheel set to get a position for the train so that it still
> > has the banking from Spline_Trans but shift over the side of the track so that
> > the wheels are above the tracks? Thanks.
> >
> >
> If I am understanding what you want, you can take points from along the
> spline on either side of a given point, together with the root point you
> can then use cross product (vcross(A,B) see the docs) to approximate a
> normal which which would reflect the banking of the spline. You would
> 'normalize it of course and then multiply by the radius of your wheel to
> get the level where the axle would be. If you don't quite understand
> what I mean, I would suggest you research what cross product is and work
> backward from there to a solution.
>
> -Jim
I think that this is just regular banking (I use Spline_Trans for that now). I
need to simulate a train where there are two wheel sets on the track. I need to
take the Spline_Trans translation and rotation for each wheel set to determine
the position of the train (the center point of the train of course will not be
over the center of the track, only the centers of the bogies). I want to carry
over the bank angle and make the train actually fit over the curve.
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HelveticaFanatic wrote:
> Jim Charter <jrc### [at] msncom> wrote:
>
>>HelveticaFanatic wrote:
>>
>>>I am modeling trains using Spline_Trans. Is there a way to average out the
>>>points above each wheel set to get a position for the train so that it still
>>>has the banking from Spline_Trans but shift over the side of the track so that
>>>the wheels are above the tracks? Thanks.
>>>
>>>
>>
>>If I am understanding what you want, you can take points from along the
>>spline on either side of a given point, together with the root point you
>>can then use cross product (vcross(A,B) see the docs) to approximate a
>>normal which which would reflect the banking of the spline. You would
>>'normalize it of course and then multiply by the radius of your wheel to
>>get the level where the axle would be. If you don't quite understand
>>what I mean, I would suggest you research what cross product is and work
>>backward from there to a solution.
>>
>>-Jim
>
>
> I think that this is just regular banking (I use Spline_Trans for that now). I
> need to simulate a train where there are two wheel sets on the track. I need to
> take the Spline_Trans translation and rotation for each wheel set to determine
> the position of the train (the center point of the train of course will not be
> over the center of the track, only the centers of the bogies). I want to carry
> over the bank angle and make the train actually fit over the curve.
>
>
Yes, see my other response. With that code snip I showed you, you
should be able to contrive an answer to your needs. It utilizes the same
macro that you would use to position an object along the spline,
including what ever bank settings you use, to predict where any point
would also be relative to the spline also. It strikes me that there is
no one way to organize this though. For instance, what do you what the
spline to actually define? The center line between the two rails? Once
you arrive at that definition, the rest should follow.
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Jim Charter <jrc### [at] msncom> wrote:
> HelveticaFanatic wrote:
> > Jim Charter <jrc### [at] msncom> wrote:
> >
> >>HelveticaFanatic wrote:
> >>
> >>>I am modeling trains using Spline_Trans. Is there a way to average out the
> >>>points above each wheel set to get a position for the train so that it still
> >>>has the banking from Spline_Trans but shift over the side of the track so that
> >>>the wheels are above the tracks? Thanks.
> >>>
> >>>
> >>
> >>If I am understanding what you want, you can take points from along the
> >>spline on either side of a given point, together with the root point you
> >>can then use cross product (vcross(A,B) see the docs) to approximate a
> >>normal which which would reflect the banking of the spline. You would
> >>'normalize it of course and then multiply by the radius of your wheel to
> >>get the level where the axle would be. If you don't quite understand
> >>what I mean, I would suggest you research what cross product is and work
> >>backward from there to a solution.
> >>
> >>-Jim
> >
> >
> > I think that this is just regular banking (I use Spline_Trans for that now). I
> > need to simulate a train where there are two wheel sets on the track. I need to
> > take the Spline_Trans translation and rotation for each wheel set to determine
> > the position of the train (the center point of the train of course will not be
> > over the center of the track, only the centers of the bogies). I want to carry
> > over the bank angle and make the train actually fit over the curve.
> >
> >
> Yes, see my other response. With that code snip I showed you, you
> should be able to contrive an answer to your needs. It utilizes the same
> macro that you would use to position an object along the spline,
> including what ever bank settings you use, to predict where any point
> would also be relative to the spline also. It strikes me that there is
> no one way to organize this though. For instance, what do you what the
> spline to actually define? The center line between the two rails? Once
> you arrive at that definition, the rest should follow.
This was for a point on each side of the train (the left and right side, thin
axis).
My situation is different.
http://www.flickr.com/photos/helveticafanatic/3001878662/
I use the spline to define the center line of the tracks. I have used
Spline_Trans to get banking which successfully rotates the train car properly.
I want, however, to not have the center of the train over the curve but the two
points where the bogies of the train are. Furthermore, the banking of these two
points must factor into the banking of the train.
Thanks.
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HelveticaFanatic wrote:
> Jim Charter <jrc### [at] msncom> wrote:
>
>>HelveticaFanatic wrote:
>>
>>>Jim Charter <jrc### [at] msncom> wrote:
>>>
>>>
>>>>HelveticaFanatic wrote:
>>>>
>>>>
>>>>>I am modeling trains using Spline_Trans. Is there a way to average out the
>>>>>points above each wheel set to get a position for the train so that it still
>>>>>has the banking from Spline_Trans but shift over the side of the track so that
>>>>>the wheels are above the tracks? Thanks.
>>>>>
>>>>>
>>>>
>>>>If I am understanding what you want, you can take points from along the
>>>>spline on either side of a given point, together with the root point you
>>>>can then use cross product (vcross(A,B) see the docs) to approximate a
>>>>normal which which would reflect the banking of the spline. You would
>>>>'normalize it of course and then multiply by the radius of your wheel to
>>>>get the level where the axle would be. If you don't quite understand
>>>>what I mean, I would suggest you research what cross product is and work
>>>>backward from there to a solution.
>>>>
>>>>-Jim
>>>
>>>
>>>I think that this is just regular banking (I use Spline_Trans for that now). I
>>>need to simulate a train where there are two wheel sets on the track. I need to
>>>take the Spline_Trans translation and rotation for each wheel set to determine
>>>the position of the train (the center point of the train of course will not be
>>>over the center of the track, only the centers of the bogies). I want to carry
>>>over the bank angle and make the train actually fit over the curve.
>>>
>>>
>>
>>Yes, see my other response. With that code snip I showed you, you
>>should be able to contrive an answer to your needs. It utilizes the same
>>macro that you would use to position an object along the spline,
>>including what ever bank settings you use, to predict where any point
>>would also be relative to the spline also. It strikes me that there is
>>no one way to organize this though. For instance, what do you what the
>>spline to actually define? The center line between the two rails? Once
>>you arrive at that definition, the rest should follow.
>
>
> This was for a point on each side of the train (the left and right side, thin
> axis).
>
> My situation is different.
> http://www.flickr.com/photos/helveticafanatic/3001878662/
>
> I use the spline to define the center line of the tracks. I have used
> Spline_Trans to get banking which successfully rotates the train car properly.
> I want, however, to not have the center of the train over the curve but the two
> points where the bogies of the train are. Furthermore, the banking of these two
> points must factor into the banking of the train.
>
> Thanks.
>
>
Okay, now that I see what you are after I would suggest to you that you
may probably not have even been successful transforming the train car
body in the general case, never mind the wheel carriages, or how the
train car would bridge between a foreward and rearward wheel carriage on
a banked curve. If you do more extensive testing you may see that
Spline_Trans cannot solve some basic issues with rotational transforms
in 3 dimensions which involve that ORDER OF ROTATON matters. It is
often necessary to do the rotation in two steps, creating an
intermediate axis in one plane using Reorient_Trans before using
Spline_Trans. I think you need to do a lot more testing.
To answer the specific question about the lateral banking of the car
body bridging a curve, you would have to know something about the actual
engineering of train cars, but in a vacuum, I would go with this:
At the center point for each wheel carriage, (single, tandem, bogie,
whatever), forward and rearward, you can establish the direction of the
banked (originally vertical) normal. Along these two directions you
would have two points at different 'heigths.' You take the bridging
lines between these points at the two heights. The halfway points of
these bridging lines, when joined, would then give the average bank that
could be used for the train car. This would DIFFER from the bank at the
halfway point along the spline.
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