12-10-2013, 06:32 AM

Some of you may already know this, but for those that don't it may be useful.

Here is some photo interpretation basics for converting a photo into usable dimensions for scratch building. This technique was used when I was working in Naval Intelligence and interpreting aerial photography of Soviet missiles in Cuba. Stereoscopic imagery was normally used, but for our use, single photos are sufficient.

It is really simple but involves a little math. To find the dimension for any height or width of a structure taken from a photograph, first find an object in the photograph that you know the actual 1:1 dimension of. The easiest is a door, which is normally 80” high. Now measure the actual dimension of the door on the photo (this can be done right from your monitor). With these 2 dimensions you can now come up with a scale factor. Let’s say that the photo dimension of the door is ¼”.

Scale factor then = Photo dimension / Actual dimension or: SF = PD / AD or .25 / 80 = .003125

This scale factor can now be used to find the actual (real life) dimension of ANYTHING in that particular photo.

Actual dimension then is: AD = PD / SF

If you want to find the length of the wall that the door is in, measure the length in the photo. Let’s say it measures 7/8”.

Actual dimension is then: .875” / .003125 = 280”

All that’s left is converting to your chosen scale by dividing by your scale ratio. For N its 160. (280” / 160 = 1.75”) So the wall, in N scale, should measure 1 ¾”. For HO its 87.(280" / 87 = 3.218").

The most common error when converting dimensions is mixing feet and inches. Keep all your dimensions in inches to make it easier.

Also, a scale factor can only be used on one photo. For another photo you must find another scale factor.

Another trick, if you have nothing to compare, is to place a yardstick in your proposed photo.

Here is some photo interpretation basics for converting a photo into usable dimensions for scratch building. This technique was used when I was working in Naval Intelligence and interpreting aerial photography of Soviet missiles in Cuba. Stereoscopic imagery was normally used, but for our use, single photos are sufficient.

It is really simple but involves a little math. To find the dimension for any height or width of a structure taken from a photograph, first find an object in the photograph that you know the actual 1:1 dimension of. The easiest is a door, which is normally 80” high. Now measure the actual dimension of the door on the photo (this can be done right from your monitor). With these 2 dimensions you can now come up with a scale factor. Let’s say that the photo dimension of the door is ¼”.

Scale factor then = Photo dimension / Actual dimension or: SF = PD / AD or .25 / 80 = .003125

This scale factor can now be used to find the actual (real life) dimension of ANYTHING in that particular photo.

Actual dimension then is: AD = PD / SF

If you want to find the length of the wall that the door is in, measure the length in the photo. Let’s say it measures 7/8”.

Actual dimension is then: .875” / .003125 = 280”

All that’s left is converting to your chosen scale by dividing by your scale ratio. For N its 160. (280” / 160 = 1.75”) So the wall, in N scale, should measure 1 ¾”. For HO its 87.(280" / 87 = 3.218").

The most common error when converting dimensions is mixing feet and inches. Keep all your dimensions in inches to make it easier.

Also, a scale factor can only be used on one photo. For another photo you must find another scale factor.

Another trick, if you have nothing to compare, is to place a yardstick in your proposed photo.