#DEMONSTRATIVE EVIDENCE
12 messages in this thread
I'm new to this forum and am looking for advice on software and hardware to
produce 3D animated videos. These videos will be used for demonstrative
evidence in legal work. Does anyone have experiece using 3D studio for this
kind of application?
Steve,
Several of us are in the midst of forming a company to do litigation graphics
on a national basis. If you are interested, call me at:
610 275-7054
or write to
Fred S. Golden
705 Gawain Rd.
Plymouth Meeting, PA 19462-2109
or CIS # 72242,1433
Fred, thanks for the response. I'll call you to learn more about your plans and
how we might collaborate.
Regards,
Give a call to Andrew Reese at Autodesk. (415/507-5632) He's in the
Tech. Pubs. dept., but also involved in forensic animation.
I am a P.E. working full time in highway accident reconstruction and have
started using 3ds for photographic measurements and animations. The animations
are usefull especially for sight distance/ time and distance questions. I have
found that my HP Scanjet IIc is very usefull. It allows the accident
photographs to be used as backgrounds in 3d models, identical photos can be
mapped onto fixed objects to allow vehicles (also mapped) to move in front of
and behind objects in the accident scene creating a realistic vedio.
I am not a 3ds expert yet but I like what I have been able to do to date. If I
can answer any questions or help you let me know,
John
John:
I'm in Oklahoma doing animations for attorneys in this area, where are working
from? I have used motion video in animations where the real vehicle goes to a
computer vehicle at impact with a computer train.
Can you explain how you can take measurements from a photograph using 3DS?
Regards……….Rick – Technical Animations
Rick, and Nancy Fulton for your next book if you are out there,
I am an Engineer working near Albany, NY. While I am sure that I will continue
to learn this is how I take measurements from photographs with 3ds:
1. Find the size of the background on your monitor. Do this by
scanning graph paper into a tif file, bringing the tif file in as the
background and rendering the scene. Count the squares on the graph
paper to determine the size of your background. Write this down and
save it.
2. Scan a photo into a tif file the exact size as your background.
This will require adding a border on two sides and scaling the photo
up. The important thing is to have the photo centered on the screen
when it is rendered Do not trim and do not allow more than minor
tiling as the photo will not be centered.
3. Create a 3d model of the scene. I use auto cadd and dxf into 3ds.
The data for the model usualy comes from record plans, surveys or
measured points in the
field.
4. Cover the 3d objects, usually the road / curb /tree trunks /poles
with a material and modify the material in the scene to a 50%
transparency.
5. Bring the police photos of the scene in as backgrounds as
described above.
6. Create a camera.
7. As you know manual methods involve marking grids on an uncut photo
to a vanishing point (center of photo).It is still best to have an
uncut photo for the background but if it was basically cut out of the
center of the origional negitive it will work. The center of the
photo is the place in the model were your camera target should be.
Place the camera about where you think the photographer was when the
photo was taken. using the photo as the background render the scene.
8. You will see the background through a 3ds model. Adjust the
camera position, target position and lens untill the two match up.
You are in the same position as the photographer.
9. Objects on 3d surfaces (skidmarks) can be measured by placing an object on
the surface and then viewing from above. Objects in space need to be set up
with photos from 2 angles.
I hope this helps,
John
Very interesting how you are taking measurements from photos using
3DS. What importance do steps 1 & 2 have with the rest of your
steps. It seems that if everything lines up in step 8 then you will
have the same result? I know I must be missing something.
What photo are you referring to in step 2 and when do you use this
info in the following steps?
For every monitor you would need to do steps 1 & 2 and keep that grid
size for future use?
In step 9, the scene would have to be flat, no elevation change, to get
accurate measurements from the objects on the ground plane, right? Maybe the
"x" and "y" coordinates would still be correct, just no "z"?
Regards……..Rick – Technical Animations
Rick,
For my monitor / scanner a 8.5" X 6.3" photograph fills the background
on a 3ds sceen. It may be the same for all but it may change for
different scanners, I don't know. The important thing is to center
the photo.
If you stood in the center of a straight flat road and photographed
the road aiming your real camera at the point where the road vanishes
into the horizon, this point would be in the center of the photo and
the paint lines would be ballanced on both sides of the centerline.
Next, if you scanned this photo into 3ds and it tiled, the center of
the photo would not be in the center of the monitor.
Now assume you place the 3ds camera on the centerline of the model and
adjust the camera so that the 3ds camera lines up with the offcenter
vanishing point on the photo. The edges of the road will not be
ballanced in the 3ds model as they are in the photo. You might be
able to move the camera to the side of the road and fudge the error
but you are not reprodusing the origional conditions. If the expert
on the other side explained this to the jury he would probably feel
better about his day in court than you would. Very ungood!
The photo in step 2 is the photo or photos you use for the backgrounds.
What ever you see in a photo is the light coming into the camera from
a unique angle. Think spherical coordnates. You don't have to but, if
you placed a long cylinder in the 3ds model, you could move and
rotate that cylinder so that in the camera viewpoint you would see a
circle, the end of the cylinder, on the point of interest in the
photo. The cylinder is now covering all of the possible points where
the light could have come from. Where the cylinder intersects an
object, flat or hill or any 3d object is where the light came from.
If you have two different viewpoints think of two cylinders
intersecting and measure the x,y,z of objects that you have no
measurements to. As with any triangulation, views at 90 degrees from
each other are going to be most accurate.
After using this method for awile I did find a paper on it S.A.E.
paper930904 It explains the theory but l feel it has shortcommings on
the practical application. Use his theory and my method.
John:
Extremely informative and interesting subject, thanks a million for the
discussion. I'm always interested in such things that relate to my job.
Thanks again!!
Regards…………..Rick – Technical Animations
Very interesting technique, John. Is that called "photogrammetry"?
(I've heard the term used before.)
I suppose it probably is. When I took a photogrametry course back in
college we had FORTRAN 77 not 3ds3. I like the look of progress. Much
of my experience comes from surveying and optics used in accident
reconstruction. Understanding how to do it the old way (by hand) made
the 3ds application a welcome improvement and much easier to explain
to attorneys.