Frequently Asked Questions

Split Camera App - Camera Calibration Procedure

Part 1 - Background


Why is Calibration Necessary?

To provide an accurate scale of photos taken with the Split Camera app, the angle of view of the camera hardware has to be known in both portrait and landscape orientation. Some devices provide values for the angles via software, however some do not and even for those that do, the values of the reported angles may not be very accurate.

Every device requires its own calibration, even if it's the exact same model as another device that has already been calibrated.

A One Time Process... But Save Your Work

Until you perform the calibration, you will be reminded that your device needs a calibration each time you run the app. Once calibrated, the values are stored in the app settings and will remain there unless the app is uninstalled.

If you do need to uninstall the app for some reason, you can re-enter the angles without having to repeat the calibration process. Once you have completed this calibration, make sure you write down the calibrated angles in case you need to re-enter them in the future.

Theory - What You're Going to Measure

Three measurements are required to perform the calibration. With the device a know distance D from a target, take a photo of the target using the device's built-in camera app (notthe Split Camera app). There needs to be something in the target, such as a tape measure, that allows you to measure the width W and length L of the resulting image.

The three measurements are the distance D, width W, and length L.

Why Use a Desk or Table?
The calibration process in the app suggests placing the device on a flat desk or table and measuring to the floor. The reason for this is to simplify the process and ensure the device is parallel to the target. However if you're able, it is recommended that you measure to a target that is approximately 3m away, instead of the <1m height of the table. For the explanation below, however, it is assumed you're using a table or desk as described in the app's calibration steps.

Units and Accuracy
It does not matter what units you use for the measurements, for example inches or centimeters or millimeters, as long as all calibration measurements are made in the same units. The units used in the calibration do not need to be the same as the units specified in the device settings for the camera height.

The more accurate your measurements, the more accurately the images will be scaled.


Part 2 - Calibration Process

Run the Calibration Wizard

Until the calibration is completed, you will be prompted to perform the calibration every time you run the app. You can re-run the calibration at any time by going to the settings and selecting the angle of view field.

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Locate a Suitable Table or Desk

The process requires you lay your device over the edge of a table (or desk) and take a picture of the floor. The top of the table should be flat with no lip, so that the device is parallel to the floor and the picture of the floor will not be obstructed by the sides or legs of the table.

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Start the Camera App

Start the camera app that came with the device. Do not use the Split Camera app for taking the following images.
Ensure that the camera is at full resolution, is set for auto-focus, and does not have any digital or mechanical zoom.


Measure the Width (Narrow Dimension)

Take A Picture
Extend a tape measure on the floor, adjusting its position and the device position so that
  • the tape is in the approximate center of the camera
  • the tape is parallel to the top & bottom edges of the camera image
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* Tip You are going to have to be able to read the numbers on the tape measure from the image, so adjust the lighting to remove any glare and ensure the tape is positioned with the graduations visible.

Read the Tape Markings
Take a picture with the camera app and open it in any image viewer that allows you to read the tape markings at both sides of the image. It may be easiest to transfer the image to a computer with a larger screen.

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Enter the Width
Do the math to calculate the width of the image and enter it in the box provided.

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Measure the Length (Wide Dimension)

Repeat the process used to measure the width of the image and measure the length.

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Measure the Table Height

Measure the height of the table, from the floor to the top of the table.

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Approve the Results

The final step shows the calculated angles and warnings if they are out of spec.

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Warnings
If there are any warnings on the summary, double check your measurements for accuracy.

The Measurement error is a comparison of the pixels/degree in landscape and portrait orientations; they are rarely exactly the same but should be within about 4% of each other.

The final angles are expected to be within certain ranges; if they are outside the range you will see an error message.


Manually Entering the Angles

The final step shows the calculated angles and warnings if they are out of spec.


 Last updated Tue, Jul 15 2014 11:00pm

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