A couple of users mentioned the camera ruler is not easy to use. So in a new version we released today, we introduced two new types of rulers – Distance Ruler and Height Ruler. The original camera ruler is renamed to Length Ruler as it can be used not just for height and distance but also for any object length (when the orientation of the length is not vertical or horizontal).

The Distance Ruler is dead simple. It is based a simple theory in trigonometry that adjacent = opposite / tan (alpha). In this case, we will use the phone accelerometer to figure out the “alpha”. The “opposite” is the phone camera height. You should measure it using a real tape as the accuracy of the value is very important. You should always hold the phone camera at the same level as your eye height. If so, you just need to measure it once. The “adjacent” will be the distance. See the picture below.

Very simple, right? Based on our experiment, the result is very accurate (offset < 1%) when the distance is not too long.  Hold the camera at the exact height is the key to the accuracy. If you are more serious about the accuracy, get a tripod and clip your phone to it. I am pretty sure you can get a higher accuracy if you do so.

The second ruler is the Height Ruler. It is a two-step process. First, we need to figure out the distance to the object. It is basically the same as the Distance Ruler. Just aim at the bottom of the object, tap the aim scope to lock the bottom. Now you aim at the top of the object. The ruler will tell you the vertical rise or the height. It is again based on the same simple triangular theory. See the pictures below for the two steps.

Here are screenshot from real use cases. The top left is Height Ruler at the second step (aiming the top). The top right is the Distance Ruler. The bottom two pictures show the exact steps for the Length Ruler. The Length Ruler is more complex to use. No wonder people complain it is too hard to use. But it can measure things that are not possible with Distance Ruler and Height Ruler. For example, a non-vertical length, or the object is not at the same horizontal level as where you stand.

Give it a try and let us know what you think. Suggestions are always welcomed.

Hei, some challenges for you guys. Can someone in Paris measure the height of Eiffel Tower using this app? Or Statue of Liberty or Empire State Building for New Yorker? Willis Tower in Chicago? Taipei 101, Oriental Pearl Tower? Post result here and we can compare it with the real results at http://en.wikipedia.org/wiki/Skyscraper.

Hint: it probably will not work if you just use the Height Ruler as the height of those skyscrapers are way taller than your eye height if you stand on the ground. The result will be very inaccurate. Here are two ways that can produce a more accurate result.

1. Standing on a high building (not as high as the skyscraper you want to measure) as well when you measure. First, standing on the ground, use height ruler measure the high building. Then stand on the high building, adjust the eye height and measure the skyscraper.

2. Use the Height Ruler to measure just 1/10th of the skyscraper, for example, to 8th floor. Then move very far away until when you hold the phone exact vertically, the whole skyscraper can still be in your camera. Now you can use the Length Ruler to take a picture of the skyscraper, adjust the screen tape to clip from ground to the place you just measured, input the height you just got. Then drag the tape to clip on the whole skyscraper to get the height of the whole building.

Have fun!