I didn't think it was possible to straighten out a photo like that into a side on view.
Any photo app that lets you get hold of the corners of a picture and pull them around can do it. I use Photoshop Elements cos it's a fraction of the price of the grown up version - and besides the blighters want a Subscription these days. But I believe there are cheaper packages that will Distort a photo just as well.
Limitations:
- You need straight parallel lines in a pretty boxy Subject,
- You can ONLY do one plane at a time,
- The photo
alone is not enough for this method.
Method:
- Project the major straight lines (running rails, cant rails, door stiles etc etc) to their Vanishing Points. Then use those VPs to Project minor straight lines towards each other, which means you can make use of crossing points that aren't actually visible in the photo at all !
- Pull all four corners of the picture until a Rectangle you are interested in become rectangular on your screen.
- Use your insider knowledge of the Subject to adjust the ratio of height to width. Eg if there's a wheel clearly visible in or parallel to you plane, adjust the ratio until it become round. Or use any other Number you have, like the ratio of height to width on a door, a numeral, a wagon side etc etc. Or use common knowledge, like the height and spacing of pairs of buffers.
- Use a separate copy of the photo for each Plane that counts. Remember that the glass in a window is further away from the camera than the frame around it, and even that small difference may be enough for you to need a separate Plane for it.
If all you don't have any fancy photo app but do have a Drawing tool that does straight lines, you can use the classic Graph Paper method:
-Find the Vanishing Points of the parallel lines and use them to Outline the significant rectangles in the Subject.
-Then draw the diagonals of each rectangle. They
must cross at the exact centre of the rectangle, right?
- Now use the Vanishing Points to draw in the vertical and horizontal centrelines of the rectangle, thus dividing it into four quarters.
- Repeat for each of the quarters giving you 16 rectangles.
- Ignore any plain boring rectangles with no detail
in your plane, and repeat again for just those that still have interest
in your plane. That gives you up to 64 rectangles within your original.
- Now get a piece of paper and draw a Chessboard on it, 8 squares by 8 squares.
- You've now got enough information to sketch your Rectangle freehand on the Chessboard.
- Of course the proportions are bound to be awry - oval wheels etc but parallel lines will be parallel and square corners will be square, which is a good start.
freehand the Plane of that rectangle (and nothing else) freehand on an 8 square by 8 square grid.
- Apply the Proportion tricks (above) to calculate what proportion the chess square ought to be for your Insider Knowlege to come right (and the wheels become round again).
- Redraw the Chessboard to that Proportion.
- Re-map the photo onto the new grid.
It's more work, but it's still easier than swallowing a textbook on Surveying and Photogrammetry :-)