Measuring Reliable DistancesOff a Digital Pic using VistaFX

There may be circumstances when due to traffic volume, weather conditions, or personal safety issues, that gathering measurements either by hand or electronic means, might not be prudent for the time/date allotted. 

There is, however, another method if certain resources are available.  Offered here are some simple steps for using aerial photographs for documenting scenes to within ‘acceptable’ or ‘significant’ limits of accuracy. 

It is axiomatic, that several measurements should be taken by conventional means at generally, all scenes whether the above ‘conditions’ apply or not.  This procedure is right out of the pages of most all Basic crash and criminal investigation manuals.

First of all, this method initially requires that a distance between two (2) known locations or ‘Control Points’ must be determined, i.e. distances between curbs, manhole covers, drains, fire hydrants, buildings (permanent or semi-permanent).

But before we get too carried away, seen here is an overhead picture taken from a helicopter, hovering over an intersection in AnyTown, USA (or, with respect, anywhere!). 

The helicopter or other means of overhead imagery, should be in a position such that the camera’s resolution (pixels - focusing) are of a high enough quality to permit, as close as humanly possible, to see the Control Points or important features of the scene, i.e. curbs, tire marks, lane markings, debris area, grid pattern, or other evidence laying on the ground.

Once the Scene has been adequately photographed and the picture is now ready for taking measurements from, we now can proceed to the software. 

Hint:  Keep track of where on your computer, the .jpg or .bmp picture is that you took of the Scene.

In VistaFX, from the top toolbar, pick the IMAGE TOOL button.

In the lower ‘properties’ dialog area, pick on the Blue button (bottom of two) that depicts a scaled image.

Then, Left-click with your mouse near the center of the Drawing Screen.

Find next, where your .jpg or .bmp digital picture of the Scene is located, then press OPEN.  Your scene should then appear on your computers screen as below. 

Note the SCALER BAR seen on the picture.   Kewl so far! J

The next thing that we do, is to move (using your cursor) the Yellow-Grip-Boxes and place them over the “knowing measurement” Control Points (curbs, drains, fire plugs, self placed Control Points [traffic cones]). 

Use the Zoom-In feature to place ‘Grips’ exactly over the established Control Points.

For this example, it is known that the distance from the top curb directly to the bottom curb is 64 feet.  The distance initially observed is just a ‘default’ unit and needs to be modified as seen in the next step.

In this example, we input the LENGTH (L =) at the screen’s lower ‘properties’ dialog box.

Once this has been accomplished, uncheck the “Show Scale Tool” or layer it to appear later if you wish it present when the final product is sent to a printer.

As seen here, the distance measurement taken between the curbs at a different location, easily falls within acceptable limits of accuracy, knowing and appreciating limitations on all measurements produced by mankind.

Measurements then can be gathered between any two points or angles, seen on the horizontal plain.  Caution – know your scene features.  Shadows, etc. can be deceiving.

For this example, we additionally have traced (as close as humanly possible) the curb/road edges, one driveway entrance and one partial sidewalk area.  We’ve too included a ‘pretend’ yaw mark just for this example.

Another viable option to creating a scaled scene diagram, is to either delete or layer the picture and what remains is the outline of the scene, with measurements and text if necessary.

Lastly, this process also permits the User to create a to-scale scene 3D Animation using either the raw, traced diagram seen just above, or the picture itself … a subject of a different paper.

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