Silhouette Measurements - Top View

[mistertate]

I need to take measurement points of the top view of cars to create an outline or silhouette. The current plan is to use a tape and plum bob but it's not very precise.
Can anyone think of a tool that could do this better without spending $20,000?

thanks,

[id10t]

park car on grid square, take photo from directly above at sufficient height to get the entire car in the frame?

Grid square is simple - some string, some paint or chalk. Mounting a camera up high is fairly simple. Perhaps do all out doors to use natural sunlight?

Is this like a "Gotta measure 2 or 3 cars" or "Gonna measure 100 different cars" ?

[GH85Carrera]

Get a UAV (drone) or a buddy with one. Shoot several photos from above. Are you trying to make a 1 to 1 size silhouette?

If you just need a shape of the vehicle reduced to a few inches just getting close to directly above will do it.

Of course the real scientific way is to do a photogrammetric survey with a UAV and then you have a full 3D model of it that can me rotated and could be used to measure very accurately. If you were in Oklahoma City I could do that for you.

[BK911]

Bright lights creating shadow on wall covered with paper, then trace the shape?

[Seahawk]

There are companies that do 3D scans for not a lot of money.

The technology has really changed: https://www.creaform3d.com/en/metrology-solutions/portable-3d-scanner-handyscan-3d

There are also a number of apps that can take photos and mosaic them into extremely accurate shapes.

AirGon - Pix4D

[MBAtarga]

Park vehicle on large paper surface. Then suspend a bright light up high on some sort of rolling base. Roll the lamp around the perimeter of the car, marking off the silhouette on the paper under the vehicle at the appropriate points - then measure distances of specific points after car is moved away.

[Tim K]

-Park on paper
-Make a large free-standing 'square' (wood, etc) with appropriate padding against car
-Mount a spring-loaded penci
-Trace car

[mistertate]

Thanks guys

[petrolhead611]

How accurate do you need it to be?i measured a few thousand cars with a tape measure over the 39 years in business as a tailored carcover maker.it was good to a quarter inch which was more than sufficient for the purpose..

[mistertate]

we're trying to get 0.1" or better accuracy. this is the data set for the car we are practicing on but would also like to have more lines of resolution:

Row0= Type=O X=142.3 Y=142.3
Row1= Type=O X=141.8 Y=141.8
Row2= Type=O X=123.2 Y=123.2
Row3= Type=O X=-15.1 Y=-15.1
Row4= Type=O X=-31.9 Y=-31.9
Row5= Type=O X=-36.3 Y=-36.3
Row6= Type=O X=-31.9 Y=-31.9
Row7= Type=O X=-15.1 Y=-15.1
Row8= Type=O X=123.2 Y=123.2
Row9= Type=O X=141.8 Y=141.8
Row10= Type=O X=142.3 Y=142.3
Row11= Type=W X=106 Y=106
Row12= Type=W X=106 Y=106
Row13= Type=W X=66 Y=66
Row14= Type=W X=66 Y=66
Row15= Type=W X=105 Y=105
Row16= Type=W X=106 Y=106
Row17= Type=W X=106 Y=106
Row18= Type=M X=82.4 Y=82.4
Row19= Type=M X=76.8 Y=76.8
Row20= Type= X= Y=
Row21= Type=M X=82.4 Y=82.4
Row22= Type=M X=76.8 Y=76.8
Row23= Type=T X=106.1 Y=106.1
Row24= Type=T X=106.4 Y=106.4
Row25= Type=T X=0 Y=0
Row26= Type=T X=0 Y=0
Row27= Type=P X=0 Y=0
Row28= Type=S X=60 Y=60

This is just a top view including tires and widnshield outline. I could see us doing 10 cars a year

[GH85Carrera]

You really need to talk to someone with a 3D scanner or someone versed in photogrammetry.

It would be quite possible to make a full on 3D model at 0.1 inch accuracy in less than several hours per car.

The investment in the software is the expensive part.

[mistertate]

I don't need a 3D model, I need coordinates of the perimeter, top view in 2D.

[GH85Carrera]

Even easier. With photogrammetry software you can make a "digital orthophoto" that will be a vertical image looking straight down.

[bleucamaro]

Originally Posted by Tim K

-Park on paper
-Make a large free-standing 'square' (wood, etc) with appropriate padding against car
-Mount a spring-loaded penci
-Trace car

Best budget method.

Gain X,Y coordinates by overlaying a grid and establishing a datum, then measure the points.
Add a small amount of automation by sectioning the paper into scannable sizes, scanning then importing into your favorite CAD package, then piece back together.

Suspending a camera above the car and photographing from above will not be accurate as you are looking at the car from a single point, centered on the car vs looking straight down at its entire periphery.

Hiring a 3D scan service may prove faster and less expensive than manually measuring yourself / imputing all that data manually.

[vash]

a $40 lazer level thing from home depot? on a tripod. you could use a hole punch and poke holes in a paper tab stuck to the car and shoot the red dot thru the hole. if you use the same offset..say 1" from the center of hole to car surface you would be pretty precise.

you know the tool. the one that shoots a red line..or dot so you can hang your family pictures all level on the wall.