Smartphone Velocimetry

Discharge is a smartphone app able to measure the average velocity of rivers and channels. It can also be used in Foundry-in-a-Box 4.0 to measure experimental water castings. Students will record videos of water pours into the clear acrylic molds and measure velocity values.

Available on both iOS and Android.

Discharge Set-up

After installing the app, new users must create a new account as part of the registration process. Registration allows users to upload their measurement results to the cloud and save data for future work.

After registration, users can setup a new site. This “site” will be recorded within the application as the GPS location where users will take future measurements.

Clicking on any particular site will open site-specific information and properties that can be further edited to suit a user’s area of measurement. The water profile shape, stream width, water depth, roughness, GPS location, and video resolution can all be modified within this menu screen.

To take a measurement, the user must first setup and mark at least 4 markers. These markers serve as a point of reference for the app during processing. All four markers must be marked within the user’s experimental setup with a bright colored marker for example. The user must then measure and input their own measurements into the app interface as described in the following images:

Note that all measurements should be inputted as meters. M1, M2, M3, and M4 refer to the four makers. W1, W2, W3, and W4 refer to the distances between the marker points and the “shore” or the point at which the water line commences. Additionally, the app interface will ask the user to measure the distances between each marker point in relation to others. Once all measurements are inputted, the user can press “set” and the app will automatically save all recorded data.

Once all marker points are saved into the interface, the user can press the “camera” icon to begin a new measurement. A camera preview page will begin and the user will be prompted to align the camera screen quadrants with the four marker points. The user can then press the record icon to begin recording a 5-second video.

After the video is recorded, the app shows a screen which asks the user to select the location of the markers. For each marker the user needs to move the hair cross exactly over the site marker. This process is described in the figure above.

After positioning the four markers, a last control view appears and by pressing the checkmark the app will calibrate the view by determining the device position and orientation relative to the site.

The water level is picked by moving the blue line to the actual water level. Pinching will zoom into the image, making it easier to click the water level accurately. As the user slides the water level up and down, in the lower part of the image the water level in metric units is shown.

After tapping on check mark, the user has the option to either delete, process, or upload the current measurement. Processing the measurement will yield the calculated discharge rate, water height, and flow velocity. The velocity vectors will also be rendered and displayed to the user. Afterwards, the user has the option to upload the results to the cloud for further data analysis.