Instructables

Measure distances on a photo using Google Sketchup

Picture of Measure distances on a photo using Google Sketchup
Some time ago a friend sent me some pictures of a printer expansion card for a brazilian ZX Spectrum. In order to produce a PCB layout for a clone of such board i needed some tool to make measurements based on a photo, and the choosen one was Google Sketchup.



Step 1: Importing the Image

Before importing the image click on the views button to select a front view.

To import an image, go to the chose the FILE->IMPORT menu option. Make sure you check the "Use as image" option. Sketchup can import several types of image, including JPG, BMP and PNG. Most digital cameras and scanners can provide a picture in such formats.

After you click in open, move the corner of the image to the origin and click the left mouse button once

Without moving the mouse, click the left mouse button again. The image will be outlined in blue. 


Step 2: Resising the image

Using the "Tape Measure Tool", extend a line along a well known measurement, by clicking once to start the tape measure and a second click ends the extension. Notice that the distance indicated on the bottom of the screen does not correspond to the actual. That's why we need to resize the image.

To resize the image, simply enter the value of the known distance. I mean, just push the numbers on keyboard. You can see the numbers while you type in the same place the original measurement were displayed before you start typing.

In the example, I knew that the board was 70mm wide, but a good reference are the distance of a DIL integrated circuit. Just remember that the larger the reference you use, the better precision you get.

After entering the distance, simply push enter. You will be asked if you want to resize your model. "Click YES".



 
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MikB1 year ago
While this works well for things that are flatbed-scanned or photographed dead flat, watch out for perspective distortion (shearing, trapezoidal, barrel/pincushion is worst) that can throw you off.

You should have tools in Photoshop/GIMP/Google Ketchup etc. that can correct for this if needed to make sure that right angles are square, straight lines are straight etc.

Your use of the DIL sockets as a measurement reference is spot on, 0.1" per pin, taken across as many pins as you can. Often, you find that the 0.1" grid extends to the other chips, so having taken a reference across one chip, you can extend the reference across more than one chip for more accuracy.

You could rely on old technology like that!
danjovic (author)  MikB1 year ago
Thanks for the suggestions. In Sketchup it is possible to correct perspective by using the 'adjust texture' feature. I think later I will complement this instructable or make another to demonstrate this.
Regards!