When developing objects or scenes in 3D we need to constantly move our point of view. We usually do that using the mouse and some helper keys to change modes. The problem is that it’s a 2D device, we can’t move and rotate the camera or the object efficiently as we would do in real life.

One popular solution is using a 3D mouse, such as the SpaceMouse. This device has 6 Degrees of Freedom (DoF), that is, it can move and rotate in 3D simultaneously. It’s big limitation is that while the traditional mouse can be moved all around your desktop, the SpaceMouse can only be moved (or rotated) a few millimeters, which leads to far less precise (or quick) movements depending on the chosen sensibility.

Why can’t we use the full potential of our hands? Wouldn’t it be cool to move and rotate things in the screen just like we do in real life?

That is why I started developing Lemonity, a plugin for Unity that makes possible a more natural interaction. Hand movements are captured using LeapMotion.

After a few months of coding and debugging, Lemonity is finally available on the Unity Asset Store.

One of the most important steps when doing interactive haptics is calculating collisions between the object that user is touching and all the points of interaction of the haptic device. While most force feedback devices (such as the ones from Sensable) have only one, others (like many vibrotactile gloves) have more than ten.

A important limitation we must be aware of is that the algorithm in charge of calculating the haptic response needs to run in real time up to 1000 times per second, therefore it is mandatory to speed up all the calculations as much as possible.

The use of bounding boxes is a popular solution to save valuable computation time. Taking one point in space and checking if it’s inside the bounding box can be done very efficiently. However if the point is inside the bounding box we still need to calculate the distance to the surface in order to generate a force or a tactile stimulli.

One of the most efficient ways of calculating this distance is using Signed Distance Functions (SDF). A SDF is a function that given a 3D point in space outputs the distance to the nearest surface. The distance is usually signed positive if the point is inside any object, negative if it’s outside and zero if it’s on the boundary.

For geometric figures we can define SDF’s using mathematical expressions. The great advantage of this is that the computation complexity is constant O(1) as we don’t need to loop through any data structure. Furthermore, this implicit representation is continuous and exact, unlike if it was defined with a polygonal mesh.

SDF’s of Regular Shaped Objects

The following functions in C# can be used in Unity to calculate the SDFs of regular shaped objects. As stated earlier the value is:

• > 0 the point is inside the object
• 0 the point is on the surface
• < 0 the point is outside the object

Note that we consider the objects centered at the origin of their coordinate system.

Sphere

This is the easiest one. The function returns the exact value.

float SphereSDF (Vector3 p, float radius)
{
  return radius - p.magnitude;
}

This is the visual representation of the field with isolines in the XY and XZ planes. Isolines represent regions of space where the value of the function is the same.

Cube

The following function is a simplification that provides the exact boundary. However, the distance values on the outside are approximations, as we can see in the sharp edges of the iso-lines. Depending on the application, these sharp edges of the isolines can be useful.

float CubeApproxSDF (Vector3 p, float side)
{
  return side * 0.5f - Mathf.Max( Mathf.Abs(p.x), 
         Mathf.Max( Mathf.Abs(p.y), Mathf.Abs(p.z) ) );
}

The following function calculates the exact SDF. Note the curved edges of the isolines on the outside.

float CubeExactSDF(Vector3 p, float side)
{
  Vector3 s = new Vector3(side, side, side) * 0.5f;
  Vector3 q = Abs(p) - s;
  return -Max(q, 0.0f).magnitude - 
    Mathf.Min(Mathf.Max(q.x, Mathf.Max(q.y, q.z)), 0f);
}

Cylinder

Like in the previous case, this is the function with sharp isolines:

public static float CylinderApproxSDF(Vector3 p, float radius, float height)
{
  return Mathf.Min( radius - Mathf.Sqrt(p.x * p.x + p.z * p.z), 
        height * 0.5f - Mathf.Abs(p.y) );
}

Function with the exact SDF:

public static float CylinderExactSDF(Vector3 p, float radius, float height)
{
  float l = (new Vector2(p.x, p.z)).magnitude;
  Vector2 v = new Vector2(l, p.y);
  Vector2 w = new Vector2(radius, height * 0.5f);
  Vector2 d = Abs(v) - w;			
  return Mathf.Min(Mathf.Max(d.x, d.y), 0.0f) + Max(d, 0.0f).magnitude;
}

Cone

Function with sharp isolines:

public static float ConeApproxSDF(Vector3 p, float radius, float height)
{
  return Math.Min(radius * (0.5f - p.y / height) - Mathf.Sqrt(p.x * p.x + p.z * p.z), height * 0.5f - Math.Abs(p.y));
}

Function with the exact SDF

float ConeExactSDF(Vector3 p, float h, float r)
{
  Vector2 q = new Vector2(new Vector2(p.x, p.z).magnitude, p.y);
  Vector2 k1 = new Vector2(0f, h);
  Vector2 k2 = new Vector2(-r, 2f * h);
  Vector2 ca = new Vector2(q.x - Mathf.Min(q.x, q.y < 0f ? r : 0f), Mathf.Abs(q.y) - h);
  Vector2 cb = q - k1 + k2 * Mathf.Clamp01(Vector2.Dot(k1 - q, k2) / k2.sqrMagnitude);
  float s = (cb.x < 0f && ca.y < 0f) ? -1f : 1f;
  return s * Mathf.Sqrt(Mathf.Min(ca.sqrMagnitude, cb.sqrMagnitude));
}

Pyramid

Function with sharp isolines

public static float PyramidApproxSDF(Vector3 p, float side, float height)
{
  return Mathf.Min(side * 0.5f * (0.5f - p.y / height) - Mathf.Max(Mathf.Abs(p.x), Mathf.Abs(p.z)), height / 2f - Mathf.Abs(p.y));
}

For the sake of completeness, I’ve used the following functions in the SDF implementations:

static Vector3 Abs(Vector3 p)
{
  return new Vector3(Mathf.Abs(p.x), Mathf.Abs(p.y), Mathf.Abs(p.z));
}
static Vector3 Max(Vector3 p, float v)
{
  return new Vector3(Mathf.Max(p.x, v), Mathf.Max(p.y, v), Mathf.Max(p.z, v));
}
static Vector3 Min(Vector3 p, float v)
{
  return new Vector3(Mathf.Min(p.x, v), Mathf.Min(p.y, v), Mathf.Min(p.z, v));
}
static Vector2 Abs(Vector2 p)
{
  return new Vector2(Mathf.Abs(p.x), Mathf.Abs(p.y));
}
static Vector2 Max(Vector2 p, float v)
{
  return new Vector2(Mathf.Max(p.x, v), Mathf.Max(p.y, v));
}
static Vector2 Min(Vector2 p, float v)
{
  return new Vector2(Mathf.Min(p.x, v), Mathf.Min(p.y, v));
}

Moving, Rotating and Scaling SDFs

We can move, rotate and scale these mathematical primitives changing any point defined in world coordinates to the local coordinate system of the SDF.

Considering a SDF with arbitrary rotation q, position v, and scale s, the following function gets the local coordinates of point.

Vector3 WorldToLocalCoordinates(Quaternion q, Vector3 v, Vector3 s, Vector3 point)
{
  Vector3 sInv = new Vector3 (1f/s.X, 1f/s.Y, 1f/s.Z);
  return sInv * ( Quaternion.Inverse(q) * (point - v) );
}

Combining SDFs

SDF can be combined and transformed in many ways. For instance, we can do Constructive Solid Geometry defining the following operations:

Union

float Union (float a, float b)
{
  return Mathf.Max(a, b);
}

Intersection

float Intersection (float a, float b)
{
  return Mathf.Min(a, b);
}

Difference

float Difference (float a, float b)
{
  return Mathf.Min(-a, b);
}

More Information

Find more interesting SDF definitions and transformations at the website of Inigo Quilez.

Visualizations have been made with a modified version of the SDF Inspector, powered by ShaderToy.

It’s time to improve my workspace. The lab is the place where I work and have fun and the same time. Wherever I lived I created a space to tinker with electronics. Now that I have my own house, it’s time to invest a little bit more. Here is a quick overview of them.

First I conquered my parents’ basement:

When I moved to my own place I started being cautious (you know, I don’t live alone…). I modified a standard wardrobe adding shelves, light and an anti-static mat. I also made a custom standing desk to fit the gap.

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It was cool but soon it started to feel too small, specially after buying my new 3D printer. Some time later I moved the custom wardrobe out of the room and made my own desk.

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Note that I modified my old standing workbench and put it sideways in order to increase the space available. I had a workspace of 1.10 x 0.5 metres for electronics (blue mat). The new bench is 3.30 x 1 metres. That’s a big change! The top layer is made of the AC6 laminate flooring, so I expect it to be durable and look good.

Now I can add keep improving my electronic lab adding more equipment if I need to :).

I’m not a big fan of public appearances, but sometimes I make exceptions. I think it can be good for young people to see engineers making stuff. In a sense that’s also one of the objectives of this website.

Link to the interview (In spanish)

I’ve been asked many times about the history of Gloveone, and how it was conceived. That’s why I’ve digged in the past to let you know how it happened and how it evolved. 

Hello Glove! SensaGlove v0

I was in the last year of BsC when José Pascual Molina, professor and one of the founders of the LoUISE research group at Castilla-La Mancha University (UCLM)talked to me about one problem they had at their Virtual Reality laboratory in Albacete (Spain). They had experience with many Virtual Reality devices such as head mounted displays, tracking systems, and gloves. However, all these devices were focused on the sight and hearing senses, and none of them let the user interact naturally and feel what they touched on their virtual environment. There were some haptic gloves available in the market but their features were very basic, and the price was unaffordable even for the University. For that reason, he proposed me to develop our own haptic glove. 

Even though my background was focused on Computer science, I was very interested in Electronics as well, so I started creating a quick and ugly proof of concept. This is how SensaGlove v0 was born. The electronics were assembled on a breadboard and relied on the parallel port to be connected to the PC. It had 3 ERMactuators (vibrators) on top of the thumb, index and middle fingers. Their intensity could be independently modulated by the software, and this vibration strength could be seen thanks to some LEDs included. 

SensaGlove v1

The refined version of the glove was part of my BsC final project, and it was called SensaGlove v1. All the electronics were confined to a small box and lycra fabric was used to increase the comfort. One of the main features of this glove was the possibility of attaching the actuators to other off-the-shelf datagloves. With this approach, tracking would be performed by the third party glove and haptics would be played with SensaGlove.  

SensaGlove v2

Once I finished my BsC I started working on different projects at the UCLM thanks to Pascual González, professor and founder of the LoUISE research group. Some of my colleagues at the University were doing their MC at the same time, so I decided to improve SensaGlove and let them use it in their own projects. In particular, it was integrated in a Collaborative system with multimodal feedback created by Arturo García and in a Model of interaction for CVEs created by Diego Martínez.

This version used an Arduino microcontroller, which was a quick way to boost the development of the electronics and to provide USB capabilities. Also, smaller flat ERM actuators were fitted inside the glove to improve the perceived sensations. 

None of these three versions of SensaGlove were able to perform finger tracking by itself. Instead, they had contact patches on the fingertips to detect pinch gestures, ie. pressing the thumb against any other finger. The hand tracking (rotation and position of the hand in space) was achieved by placing an electromagnetic sensor from the Flock of Birds tracking system.

SensaGlove v3

In 2009 I started my Ph. D. advised by J.P. Molina and P. González. I focused it on the improvement of vibrotactile sensations for virtual environments. As I needed more tracking precision, I created a new version based on the optical tracking provided by an Impulse PhaseSpace. 

Vibrotactile technology was also pushed to the limits. To accomplish that, I created a 16 channel ERM controller with overdrive and braking capabilities. These methods were introduced in order to reduce the start and stop latency of the motors, improving the haptic response felt by the user. This controller, was also part of a generic vibrotactile tool named VITAKI (VIbroTActile KIt). 

SensaGlove v4

Next revision of the SensaGlove controller introduced two major upgrades. The circuit was properly routed on a single PCB, and more importantly, it featured an scalable feature: more vibrators could be connected by stacking shields on top of it (up to 16 actuators per layer). It also provided a “volume” knob to adjust the overall vibration intensity perceived by the user. 

SensaGlove v5

In 2014 SensaGlove went wireless. The controller form factor was heavily reduced while keeping the overdrive and braking features. As a drawback only 10 vibrators were supported. A battery, charger and bluetooth module were added to go fully wireless. The proof of concept design had three PCB’s (microcontroller, ERM drivers and bluetooth) wired and fitted together in a single enclosure.

SensaGlove v6 / Gloveone rev 0

I redesigned SensaGlove v6 to be used with an affordable Leap Motion tracking system. The electronics were very similar to SensaGlove v5, the only difference was that the three PCBs were routed together to reduce the wiring. 

I joined Neurodigital in November 2014 to keep improving the glove and we changed its name to Gloveone. This is one of the first public appearances of Gloveone:

• http://www.rtve.es/noticias/20141203/gloveone-guante-permite-tocar-sentir-realidad-virtual/1060560.shtml.

A new white version optimized for Leap Motion can be seen here:

• http://uploadvr.com/return-of-the-glove-neurodigital-technology-seeks-to-bring-gloves-back-to-vr-with-the-gloveone/
• http://www.teleprensa.com/almeria/neurodigital-technologies-desarrolla-un-pionero-sistema-de-estimulacion-multisensorial-para-rehabilitacion-neurologica.html
• http://www.techradar.com/news/gaming/i-just-played-catch-with-an-invisible-baseball-but-it-felt-like-it-was-real-1275157

Gloveone rev 1

For the second revision of Gloveone I reduced the form factor of the circuit so that it could be placed on top of the hand.  

Gloveone rev 1 was shown to the public at the Fun & Serious game festival of Bilbao in December 2014.

What’s next?

Neurodigital launched a Kickstarter campaign during 2015’s summer.

One year later we added IMU-based finger and arm tracking, which was shown at E3 2016.

Soon after the glove was renamed as AvatarVR and Gloveone dissapeared from Neurodigital’s website.

Unfortunately there is still controversy around the Kickstarter campaign, with many backers asking for their rewards.

By the end of 2016 I decided to quit Neurodigital and started working as a freelance.