Calculating the conversion factor based on the drawing scale and the scanning resolution

When we speak about pixel we mean the image resolution in pixels per inch used to scan the image, not the pixels shown on the screen, which can vary according to the zoom.

Example 1:

The image file was scanned at 200 dpi, and the scale of the drawing is 1:2000.

How to determine the conversion factor to obtain an area calculated in m2?

Solution:

200 pixels in the image = 2.54 cm (1 inch) in the map =  2.54 cm * 2000 in the real word.

2.54 * 2000 = 5080 cm = 50.8 meters

Therefore:

200 pixels in the image = 50.80 m in the real world

1 pixel in the image = 50.80 /200 = 0.254 m in the real world

So the conversion factor go get measurements in meters is 0.254. That means that each meter is about 4 pixels long in the image.

Example 2:

The image file was scanned at 300 dpi, and the scale of the drawing is 1:10000.

How to determine the conversion factor to obtain a measurement calculated in feet?

Solution (rounding to two decimals to simplify the example):

300 pixels in the image = 1 inch in the map =  1 * 10,000 in the real word.

10,000 inches = 833.33 feet (10,000 / 12)

Therefore:

300 pixels in the image = 833.33 .feet in the real world

1 pixel in the image = 833.33 /300 = 2.78 feet in the real world

So the conversion factor go get measurements in meters is 2.78. That means that each pixel in the image is equal to 2.79 feet in the real world.