Win 7 Paint, Digital Camera and Carpenter Level

Harvard wrote:

mich800 wrote:
A square and a ruler would not work?

For sure, here is the data from Win Paint:

For example, using Win Paint, find the two x,y coordinates:

1024, 1189px
1530, 1190px

Notice they both fall on the top of a parallel redish/orange banner in the center of the picture.

TANGENT = OPPOSITE / ADJACENT
OPPOSITE = 1190 - 1189 = 1 pixel
ADJACENT = 1530 - 1024 = 506 pixels
TANGENT = 0.001976284
ARCTAN 0.001976284 = 0.1132 Degrees.

So I have a 1 in 506 resolution.

I meant more from an actual measurement with a carpenters square from the ground and using simple geometry. Trig is not my strong suit. I guess you would need to deal with the tire bulge so maybe us some sort of standoff on the wheel to make the measurements.

mich800 wrote:
A square and a ruler would not work?

For sure, here is the data from Win Paint:

For example, using Win Paint, find the two x,y coordinates:

1024, 1189px
1530, 1190px

Notice they both fall on the top of a parallel redish/orange banner in the center of the picture.

TANGENT = OPPOSITE / ADJACENT
OPPOSITE = 1190 - 1189 = 1 pixel
ADJACENT = 1530 - 1024 = 506 pixels
TANGENT = 0.001976284
ARCTAN 0.001976284 = 0.1132 Degrees.

So I have a 1 in 506 resolution.

i would not set my wheels myself using this method
i doubt the angle numbers in the picture will be an exact match for the alignment numbers from the shop

BUT, as a reference guide to know when the wheels might need re-alignment

first have them aligned, or know that they are aligned

take your pictures
record all camera settings, distance, everything
using paint draw lines in a "copied" set of pictures, not to measure exact angles, but to make templates

whenever you want to check alignment take new pictures using the exact distance and position settings

draw lines on the new pictures

see if they match

A square and a ruler would not work?

tatest wrote:
I think I see a lot of barrel distortion in that photo, making it difficult to draw any conclusions about what is level. That's pretty typical for the low-cost zoom lenses in digital cameras, to go from severe barrel distortion at one end of the zoom to severe pincushion distortion at the other. Some manufacturers try to correct this in post-processing of the digital image, looks like your camera does not.

With this much distortion, I think it would be pretty difficult to say much about what is level based on pixel coordinates. Don't pick just two points, follow the edge of the building roof all the way across. I think the change in Y coordinates as you go across is going to show you the roof as bow-shaped, opening downwards. Any two points, even if the camera is level, Y is going to depend on where you are on the distorted curve.

I agree on everything you have posted. The way I get around these issues in the intended application (wheel camber) is to:

1. Center the camera lens horizontally in line with the near vertical camber angle I wish to capture.

2. Position the camera lens vertically on a stand (which is parallel to the ground) in line with the wheel axel.

3. Position the camera about 5-6 feet from the wheel.

4. Restrict the area of the Win Paint x,y coordinates to the center of the picture, in other words avoid the extremities.

All my the fender shots show every distortion you have pointed out. The saving grace is they need to be only within +/- 2 degrees or so to still be useful.

My mall shot was meant to illustrate the relative reliability of measuring the center only. Naturally, I am assuming the mall is level and the 0.11 Degrees is my error in interpreting the bubble level.

At any rate, my target measurement estimation is only meant to provide a GO (less then -4.0) or NOGO (greater then +4.0) trip to a professional alignment service

Again, I do appreciate your input here, please respond if you think I could improve on this technique.

I think I see a lot of barrel distortion in that photo, making it difficult to draw any conclusions about what is level. That's pretty typical for the low-cost zoom lenses in digital cameras, to go from severe barrel distortion at one end of the zoom to severe pincushion distortion at the other. Some manufacturers try to correct this in post-processing of the digital image, looks like your camera does not.

With this much distortion, I think it would be pretty difficult to say much about what is level based on pixel coordinates. Don't pick just two points, follow the edge of the building roof all the way across. I think the change in Y coordinates as you go across is going to show you the roof as bow-shaped, opening downwards. Any two points, even if the camera is level, Y is going to depend on where you are on the distorted curve.

Thanks rk911, you are spot on, it is indeed a hobby. :):):)

Harvard wrote:

MrWizard wrote:
angles of what ?

this is a test..

the question is to what purpose ?

i would not attempt to construct a building using this method
NOR would i attempt to survey property with this method

you want to measure angles somewhere else
to what purpose ?

I want to measure the angle a given front wheel makes with a vertical datum, otherwise called camber. I think you missed my link in my previous post.

well, everyone needs a hobby! :)

MrWizard wrote:
angles of what ?

this is a test..

the question is to what purpose ?

i would not attempt to construct a building using this method
NOR would i attempt to survey property with this method

you want to measure angles somewhere else
to what purpose ?

I want to measure the angle a given front wheel makes with a vertical datum, otherwise called camber. I think you missed my link in my previous post.

angles of what ?

this is a test..

the question is to what purpose ?

i would not attempt to construct a building using this method
NOR would i attempt to survey property with this method

you want to measure angles somewhere else
to what purpose ?