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I found an interesting problem that I thought would be amenable to Fortran solution.

At work we often get pictures taken of bridges and such and we have some dimensions. I had one of these problems yesterday from a small reinforced concrete bridge in Italy.

A picture taken at an oblique angle had the pier widths as 40 and 150 pixels each. Each pier is 250 mm in width -- thankfully humans like roundish numbers

The total is 1350 pixels - how long is the opening between the piers. Picture attached in Zip file.

it is a simple exercise in geometry that is estimable with Autocad, but a Fortran solution of the problem would be interesting.

I think you could set it up as the intersection of two lines, the line along the photograph at the measurement points, the horizontal line which has the true ratio of the dimensions, these meet at a point B which is on radial line from the vanishing point --- and then the radial lines from the vanishing point should be calculable?

I have to go to teach class and I have a paper due out -- but it was an interesting thought experiment. I think finding B is the critical step and the angle.

John

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PS I got 4.6 metres

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