Knowledge Base

Article Number: 47 | VC4 | VC3 | Post Date: November 7, 2017 | Last Updated: March 7, 2018


Is there an easy way to measure arc lengths, path lengths, and angles? 

ARC and Path Lengths

As of the November 25, 2017 Virtual CRASH 4 auto-update, lines, polylines, curves, and arcs will report their x-y projected lengths in the bottom status window as they are being drawn or modified. Lines and arcs now have a length attribute in the misc menu. This is demonstrated below. 

Additional, when the cursor hovers over these objects the length as well as distance from start and distance from end of the path will be displayed. 

Below you will find the original reply to this question prior to the November 25, 2017 update. The method described below can used in VC3 and VC4. 


For straight lines, the "Dimension Line" tool is the easiest way to measure lengths; however, for VC3, the easiest way to measure arbitrary path lengths is to use the axes tool (note, you can learn more about the axes tool with the Virtual Tutor: help > helpers > axes). The axes tool can then be made to conform to an arbitrary path shape by using the “pick node” feature. In the example below, an arc is drawn, with angular span from 22.026 degrees to 156.316 degrees (angle = 134.29 degrees). The radius is 8.238 ft. The expected arc length therefore is given by \( {134.29 \over 360} \times 2\pi \times 8.238 ft = 19.308 ft \). Once the axis is drawn, simply left-click on “pick node” then left click on the path, and the axes tool’s x-axis will conform to the shape of the path. 

You can exactly overlay the axes tool on top of your path by setting the position-local values of the axes tool to the same value as the path.

You can add points to the axes tool. Each point’s (x, y) coordinate is set with respect to the axes tool’s x-axis and y-axis. Here the tool’s x-axis is made to follow the arc shape. Three points are placed in the space of the axes tool. Points are added by simply left-clicking on the “add” button. Each point starts at (0,0), but can then be moved either by changing the x and y coordinate in the left-side control panel, or by left-clicking on the point, holding the mouse button, and dragging the point to the desired location. Here the final point, labeled “to find arc length” was placed at the end of the arc. You will note you cannot drag the point past the end of the path if “pick node” is used. Therefore, we naturally arrive at a measurement of the arc’s length just by reading off the x coordinate for this point. Here we see a value of 19.308 ft, as predicted. 

The process is shown in the video below. 


Measuring Distances in 3D

A 3D measuring tool will be released as a future update for Virtual CRASH 4. For now, one can use the path animation tool to make measurements in 3D. The path animation tool can snap to pointset points as well as to terrain meshes. In the example below, we have a terrain mesh created with the Easy Surface Builder tool. Suppose we want to measure the length of the tire mark on the terrain surface, which isn’t perfectly flat. First, using the Path Animation tool, we draw a path along the tire mark, using just four control vertices. Remember, the path animation tool creates a 3D spline path using your control vertices. The z-position of each vertex will be determined by the terrain mesh position beneath the control vertex.

In the path animation sequence menu, you can left-click, hold, and drag your mouse over all of the sequence entries to select them all at once, then press “remove sequence” to remove them. This will make things a little easier to see.

Ensure that the spline curve type is “spline fit” so that the path is forced through the control vertices, which generally will be placed on visible marks of interest in the scene. 

Figure3D_FIT.png

Next, in the select type drop down menu at the top, select “Sequences”. In the path animation sequences menu, enter “0” into the “distance offset” input field. You should now see an “I” and “t0” icon appear at the start of your path. 

Figure3D3.png

Left-click on the “I” icon, hold, and drag the icon along the path. In the sequences menu in the left-side control panel, note as you move your mouse, the “distance offset” value changing in real time. The distance offset value is distance between the start of your path (the first control vertex you made), and the “t0” icon. 

Finally, drag the “I” all of the way to the end of your path. Now, the “distance offset” is the total path length. 

Using this same method, you can obtain 3D path length estimates from total station data as well. First, deselect “Grid Point” and “Grid Line” and select “Vertex” in the snaps menu, then left-click on “Snaps Toggle” to enable snapping. 

Note: If you’ve enabled the “triangulate” feature to create a surface mesh and enabled the mesh as a terrain object (from Physics > Make Unyielding / Terrain from Selection), and you want to measure distances along the points themselves rather than using the surface mesh, you’ll need first remove physics (Physics > Remove Physics from Selection) from the point set to prevent the path animation tool from automatically snapping to the terrain mesh rather than your total station points. You’ll also need to disable the triangulate feature to see the total station points. Once you’ve completed your measurements, simply re-enable triangulate, and re-select Make Terrain from Selection. 

Here we’ll try to measure the distance of this tire mark. The tire mark was measured at points. 

Create an animation path as before. We created four control vertices. Left-click on each control vertex and move each one toward the corresponding total station point. Virtual CRASH should automatically snap the control vertex to the point. Below you can see the four points are snapped to the total station points. 

Using the same procedure described above, we can now measure the distance from the first point in the path using the “I” icon and the “distance offset” value. Dragging the “I” icon to the end of the path will give us the total path length, which in this case is 11 feet. In the example below, we’ve hidden everything but the total station points and animation path to show that the animation path is indeed created by fitting a spline path to the total station points in 3D. 


Measuring Angles

Currently, the easiest way to measure angles between objects is to simply draw a line connecting your reference point to your objects. In this case, we set up another axes object so that the origin as our reference point (note the snap to vertex option was used to ensure the line’s start point snapped to the reference point). A line is then drawn from the reference point to the red vehicle. Another line is drawn from the reference point to the blue vehicle. The yaw value in the rotation-local menu for a line is the line’s angle with respect to the global x-axis. So, simply taking the difference between these yaw angles in our example gives the angle between vehicles with respect to the reference point. In this case, the angle between the vehicles is \(51.448~deg – 11.478~deg = 39.97~deg \).


Tags: Measure length, measure distance, arc length, measure angles, measuring tool. 


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