Introduction: 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".
Step 3: Measuring
After resizing the model, you can use directly the "Tape Measure" or the "Dimension" tool on the board. In the example I have measured the diameter of a hole in the board.
In the photo I have measured the diameter of a hole and the distance from the center of the hole to the edge of the board.
That's it. Simple Like that.