HOW TO SET A BOUNDING BOX
by Cyndi Richards
I know, first question, what is a bounding box? A bounding box is used to
determine what part of the wagon or locomotive is solid. One bounding box
cannot pass through another bounding box. It will result in a collision and end
of the activity. In MSTS if the bounding box of one car is close to the
bounding box of another car a collision will result when these cars are taken
through sharp curves or switches. What happens is that one bounding box comes
into contact with another bounding box. Note of interest here, if the collision
speed is less than the maximum coupling speed, usually 3 mph,
the activity will not end.
Before getting to the step by step part I have to put forth some
observations and a few tips to make life easier. I am going to show you how I set up a bounding box. Others
have their ways, the way that you choose is up to you. The width and the length
of the bounding box is set from the central axis of the model. The height is
set from the bottom of the bounding box to the top of it. Instead of confusing
you with x, y, and z positive and negative offsets, I will put it this way.
Total width is determined by placing one half total width on each side of the
model centerline. Length is determined the same way. If you know rocket science
then the width is x, negative offset is left of centerline, positive offset is
to the right. The length is z, negative offset to the rear of centerline,
positive offset to the front. y is the height of the bounding box starting at
the ground, not the top of the rail. The utility program Bounding Box Editor, available in the
file library, is an excellent program. It can also be used to do what we are
doing here.
TIPS:
You will be doing a lot of switching back and forth between MSTS and the
.sd file you are working on. I do the following. Open the folder of the wagon
you are working on, then minimize it. Run the sim to see what adjustments have
to be made to the bounding box. Exit the activity back to the Route Selection
screen. Press the ALTERNATE and TAB keys. This will minimize MSTS and bring up your wagon folder. Make your
adjustments to the .sd file, save and exit, minimize folder. Maximize the sim
and click START or press ENTER. Using
this procedure, you won’t have to restart the sim every time you make a change.
When the sim is running and your train is on the screen, you have to turn
on the BOUNDING BOX DISPLAY. Do this by holding down the CONTROL key and pressing the + on the
NUMBER PAD. This sequence will also turn off the display. The
red lines in the display will show the outline of the bounding box. To properly
check the length, width, and height you will have to line up the front
red indicator line with its rear red indicator line. It takes a light finger on
the arrow keys to rotate the camera and get your two lines into one. Using the
number two or three view will not give a precise and exact placement setting.
However, it will be close enough for our purposes. While I am babbling on here,
I’ll tell you why. In the number two and three views the focal point of the
camera is on the center of the wagon. While all the other camera parameters can
be changed, the focal point cannot.
ABOUT THE SHAPE DEFINITION_< .SD > FILE
When you open the .sd file, the only line we are interested in right now
is the last line, as shown below:
ESD_Bounding_Box ( -1.95 0.1 -6.99 1.9 4.96 7.03 )
What
do these numbers mean? Thought you would never
ask.
Starting from the left, they mean:
-1.95 = distance from the centerline to the left side of the
wagon.
0.1 =
the lower height of the bounding box as measured
from the ground.
-6.99 =
distance from centerline to rear of wagon.
1.9
= distance from centerline to right side of
wagon.
4.96 =
the upper height of the bounding box as measured
from the ground.
7.03 =
distance from the centerline to front of the wagon.
All
numbers represent meters, not yards.
OK LET’S DO IT
STEP
1: Grab a pencil & paper
STEP
2: Open the wagon folder you are going
to work on, then
Open the .wag file. Look for
this line:
Size ( 3.1m 4.6m 13.32m ) (your numbers will
be
different)
Write these numbers
down for later. The first number
is the width of the wagon. The second number is the
height of the wagon, and the third
number is the
length of the wagon. Close .wag file.
STEP
3: Now run the sim, put your consist on
the screen,
turn on the Bounding Box Display and
hit 3 key.
As photo # 01 shows, the bounding box
is too long
and too high.
Photo
# 02 shows a close up of the bounding box length.
STEP
4: We will start by adjusting the
length of the bounding
box. From the numbers you wrote down
from the size
line, take the third number and
divide it by two.
In the example above the length size
was 13.32m
Dividing by 2 gives us 6.66.
STEP
5: Open the .sd file and change
the third number to
the result of your division; be sure
to retain the
minus sign. Do the same for the sixth
number, but
without the minus sign. Using the
above example:
Before;
ESD_Bounding_Box ( -1.95 0.1 -6.99
1.9 4.96 7.03 )
After:
ESD_Bounding_Box
( -1.95 0.1 -6.66 1.9 4.96 6.66 )
STEP
6: Return to the sim and turn on the
bounding box display.
Photo # 03 shows that the box has
been shortened.
Photo # 04 shows what I consider to
be the proper
location for the length. That is at the outer edge
of the draft gear box, also called
the coupler
pocket. You will probably have to adjust the numbers
several times to get it in the right
place. So always
remember:
INCREASE OR
DECREASE THE 3RD & 6TH NUMBERS BY THE SAME
AMOUNT. THEY
SHOULD BOTH BE THE SAME NUMBER.
STEP
6: Now that we have the proper length,
and you are
feeling rather confident, lets adjust
the width.
Photo # 05 shows the best view for
making any
adjustments to the width which should
be along
the outer edge of the sides.
STEP
7: From the numbers you wrote down from
the size line,
take the first number and divide it
by two. In the
example above the number is 3.1m,
dividing by two
gives us 1.55.
STEP
8: Open the .sd file and put the result
of your division
In the first and fourth places as
shown below.
Before:
ESD_Bounding_Box ( -1.95
0.1 -6.66 1.9 4.96 6.66 )
After:
ESD_Bounding_Box ( -1.55
0.1 -6.66 1.55 4.96 6.66 )
STEP 9:
Close the .sd file and run the sim. Photo # 06 shows
a correct bounding box width.
Adjust the width as
needed remembering to increase or decrease the
numbers by equal amounts.
STEP
10: Now we are going to adjust the height of the bounding
box, which is the easiest part. At
this point I want
to thank Joe Morris and his team of
rocket scientists.
Without getting technical on you, let
me just state
that as a result of testing, the
proper height at
bottom should be 0.9m. This places
the bottom of the
box at prototype height. I use this
as my standard as
I believe it will be the standard of
the future.
So using our sample .sd file, change
the second
number to 0.9 as shown below:
Before:
ESD_Bounding_Box ( -1.55 0.1
-6.66 1.55 4.96 6.66 )
After:
ESD_Bounding_Box
( -1.55 0.9 -6.66 1.55 4.96 6.66 )
STEP
11: Now go back to our example size line and look at
the second number which is 4.6m. This
is the number
we are going to place in the fifth position
of the
.sd file as shown below:
Before:
ESD_Bounding_Box ( -1.55 0.9 -6.66
1.55 4.96 6.66 )
After:
ESD_Bounding_Box ( -1.55 0.9 -6.66
1.55 4.6 6.66 )
STEP
12: Close the .sd file and start the sim. If you refer back
to photo # 01, you can see the height
was too high.
Photo # 07 shows a correct height.
A brief note here on setting the
upper height.
On older wagons with a roof walk and
vertical brake
wheel, the proper height will be the top of the roof
walk. In the prototype if the brake
wheel strikes an
object, it will not normally cause a
derailment.
If the wagon has a peaked roof, set
the height to
the top line at the top of the peak.
Rotating the
camera to end view will be of some
help.
STEP
13: CONGRATULATIONS! You have just set up a proper
bounding box.
While
I have used a wagon file in this example, the same procedure applies to locomotives.
I
hope you have found this guide both informative and easy to use. Again, special
thanks to Joe Morris and his team.
Cyndi Richards
BNSFLADY2081@aol.com
