Rectified image of experimental site.

<p>(a), (b), (c), (d) are the rectified images corresponding to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127018#pone.0127018.g005" target="_blank">Fig 5</a>.</p

Relative error of the length of each side of the quadrangle.

<p><i>AB</i>, <i>BC</i>, <i>CD</i>, and <i>DA</i> denote the relative measuring error of each side of quadrilateral ABCD. Δ<i>l</i> is the length of the horizontal and vertical spacing of feature points on the small calibration object.</p><p>*The average value</p><p>Relative error of the length of each side of the quadrangle.</p

Geometry model of camera imaging.

<p>Geometry model of camera imaging.</p

Measurement comparison between the hands-on method and the proposed method.

<p><i>A</i>, <i>B</i>, <i>C</i>, and <i>D</i> denote the breaking trace mark in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0127018#pone.0127018.g014" target="_blank">Fig 14</a>.</p><p>Measurement comparison between the hands-on method and the proposed method.</p

Relative error of the length of each side of the quadrangle.

<p><i>AB</i>, <i>BC</i>, <i>CD</i>, and <i>DA</i> denote the relative measuring error of each side of quadrilateral ABCD. <i>L</i> is the length of the composite calibration object.</p><p>*The average value</p><p>Relative error of the length of each side of the quadrangle.</p

Rectified image of traffic accident site.

<p>Rectified image of traffic accident site.</p

Flow chart of the improved 2D-DLT method.

<p>Flow chart of the improved 2D-DLT method.</p

Photo of traffic accident site.

<p>Photo of traffic accident site.</p

Sketch map of the experimental site.

<p>Sketch map of the experimental site.</p

Photo of experimental site.

<p>Four field images were taken as the length <i>L</i> of the composite calibration object varied from 1.0 m to 4.0 m. (a) 1.0 m, (b) 2.0 m, (c) 3.0 m, (d) 4.0 m.</p