0.21.11 iOS release: New basic measuring tool

[matlabbe]

Sometimes we want to measure something but we don't have a ruler or a measuring tape, but we have our iPhone Pro. AR measuring tools can be tedious to use because it is difficult to know if the camera drifted while taking the measure or that we clicked the right thing. With RTAB-Map iOS, the measuring tool is done in VR after you scanned your room or something you want to measure, so you can make sure that the mesh looks good and correctly optimized with loop closures (to decrease VIO drift) before doing the measuring. Here are the steps to correctly use that tool.

1. The tool is available only after generating the optimized mesh (textured or not).

2. To make the measuring axis snapping feature working correctly, before clicking the tool, align the grid with the walls or planes you want to measure by clicking on Ortho view. Note that you can switch to Ortho view after clicking on measuring button. Tip: Pinch out to increase the field-of-view.

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3. Click on the Measuring button, you will jump in VR mode with a square showing on the surface you are pointing on. If the square turns red or green, it is align with the grid (either x or y axis). Blue squares are for z-axis. The measuring buttons mean:
   

4. To add a measure, click on "+" button to anchor the start on some surfaces. When you move a line perpendicular to that plane will follow you. Click again to add the measure.

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5. Depending on your "real" space, the virtual world would not align with the real walls. You can teleport in the model with the corresponding button.

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6. To remove a measure, point on one of the squares of a measure and click on "-".

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7. We don't save the measures in the model, but you can take a screenshot (volume down and power at the same time)
   
   

The measuring units can be changed in the Settings, all way down, there are metric and imperial systems: