32

I am experimenting with a graphics pen and tablet and it got me thinking about the difference between it and my mouse. One huge difference is that the tablet's working area covers the whole screen, so that you can tap on an absolute position. My mouse always outputs relative x/y from its last position. This is obviously a huge benefit because it does not restrict the mouse to one part of your desk. I am wondering if this was how the original mice/trackballs/whatevers did, or were they absolute position?

  • 15
    A useful test case for this: Move your mouse towards the top of the mouse pad, then turn it 90 degrees and move it down to the bottom. How would one capture that absolute path? At a bare minimum it either needs to encode the information on the mat or have a 3rd axis to capture the mouse turning. – Cort Ammon - Reinstate Monica Dec 4 at 4:50
  • 6
    Um, how could they possibly do absolute position? GPS onboard?? J/K, GPS doesn't have that much resolution. The mouse simply does not have the sensors to know its absolute position. This will be clearer if you throw away your mouse pad and use any available surface for the mouse. Mice don't actually need mouse pads; they are the fuzzy dice of computers. – Harper - Reinstate Monica Dec 4 at 16:23
  • 1
    @Harper-ReinstateMonica - perhaps, but the question was more general and included track balls, which could conceivably produce an absolute position (although why they would I do not know) – Michael Stachowsky Dec 4 at 16:51
  • 2
    "track balls, which could conceivably produce an absolute position" -- How could they, without knowing the size of your displays and their configuration? The mouse informs the computer of its state, but not the other way around. The computer is not going to inform the mouse when a new display is connected/disconnected or when its position changed. You could make a mouse protocol that does, breaking compatibility afforded from pre-existing mice, but it would be much more complex for no benefit. – JoL Dec 4 at 21:00
  • 4
    The “gridded” mousepads of Sun workstations could not be “absolute” as there was no way to distinguish which of the many lines you were crossing. And the optics of the mouse could detect things other than the lines. A popular prank where I worked was to put someone’s mouse against the screen. A few seconds of CRT scan would fill up the mouse buffer and lock up Solaris until all the pulses were processed. – WGroleau Dec 5 at 15:46
58

The first mouse tracked relative motion along two axes, and as far as I know all standalone mice produced since have followed suit. It would be difficult to build and use a mouse relying on absolute positioning: it would have to track its movement very accurately, with no slippage, or else allow for regular recalibration; as you mention, it would only be usable in a specific area; and it wouldn’t support varying sensitivity (i.e. slow movement being translated at higher resolutions than fast movement).

Even early optical mice, which used specific mouse mats (as used for example on Sun workstations), didn’t track their position on the mat itself, only their relative movement.

There are mouse-like devices which produce absolute coordinates: pucks on graphical digitisers. These are used on large tablets, and are not practical replacements for mice in most cases.

  • 6
    If my memory serves me correctly, early mouse protocols (for PCs at least) did not have the concept of reporting absolute positions. So not only would the hardware have been difficult, the communications protocol lacked the very idea. – JdeBP Dec 3 at 21:28
  • 7
    Aside from the space the tablet takes up, digitizers make great mice. The "File" menu or whatever is always in the same place on the tablet so you can just move the mouse there and click. – Ross Ridge Dec 4 at 2:26
  • Also note that with absolute positioning, your movement would have to be limited to the size of the mat. Mouse sensitivity would be then calculated as the proportion of screen size and mat size. That wouldn't really work well. – Sulthan Dec 4 at 9:24
  • 1
    I think it's pretty obvious a mouse has to work in relative coordinates because you can pick them up and put them down somewhere else. Without some fixed reference point, like a tablet, absolute coordinates can't possibly work. – JeremyP Dec 4 at 9:54
  • 2
    In his parting lecture, Niklaus Wirth (i.e. the guy who brought the first prototype mouse to europe) mentioned that the beauty of the mouse is that the concept still works with a low fidelity device, because the human is compensating for any positioning errors as part of a feedback loop. If the mouse pointer is not were you want it (due to hardware inaccuracy), you just move it a little bit more. On the other hand, graphical digitisers that produce absolute positions must use very accurate (and therefore expensive) hardware. – Georg Patscheider Dec 4 at 11:01
27

It was by no means a mass market device, but Hayward and Ramstein's Pantograph (1993) encoded linkage positions as absolute coordinates. It also provided force feedback, and could ‘drive’ itself based on screen contentPantograph

  • Of course there have been explicite mass market devices using similar mechanics like this ad from 1983 showing a drawing arm from 1983 for Apple, Atari, Commodore and alike. – Raffzahn Dec 4 at 11:07
  • 3
    oh my, that device (a Plot-II graphics table [sic], also sold as the VersaWriter) looks perfectly terrible! Two potentiometers on bendy plastic arms can't be very accurate: at least the disk in the picture's safe from electromagnetic graphics tablets' legendary ability to wipe disks. – scruss Dec 4 at 15:53
  • Back In The Day (tm) I had a robotic plotter that crawled around on a piece of paper, drawing as it went. Hideously inaccurate, to the point of being useless as a plotter - but it was a cool bit of tech. :-) – Bob Jarvis - Reinstate Monica Dec 5 at 3:58
  • @BobJarvis-ReinstateMonica was it that one from Linear Graphics for the Beeb? I remember those! – scruss Dec 5 at 14:05
  • 1
15

Some of the HP Omnibook series of laptops and sub-notebooks from the mid 1990s had a curious pop-out “mouse on a stick”:

HP Omnibook 800 Mouse, from 1996 manual

While hardly part of the original mouse timeline dating back to the 1960s, this HP mouse used encoders built into the computer body. The encoders — as shown in this Omnibook repair video from 10' 40" on — appear to track the extension and angle of the mouse stick. In order to produce PS/2 mouse compatible movement counter signals, the (∆r, ∆θ) from the internal encoders would have to be temporarily converted to an absolute (X, Y) position from which (∆x, ∆y) signals were derived.

From memory, the Omnibook mouse would continue to produce (∆x, ∆y) signals if it hit the relevant end stops, so there were perhaps some additional limit switches in the mouse hardware. It was a fairly terrible mouse, and completely unusable by left-handed people.

  • What an absolutely odd device. Thanks for showing it off – Michael Stachowsky Dec 4 at 17:48
  • Glad to, @MichaelStachowsky. For a while, HP were very keen on their encoder technology and this device must've gained its designer a great bonus that year as it's likely to use a couple of HP showcase components. Shame the mouse was an ergo-disaster though – scruss Dec 4 at 17:53
  • It might be more useful to readers if you concatenate the answers to give an overview about various technologies - as there are quite some. – Raffzahn Dec 4 at 20:59
  • 1
    @scruss: re “completely unusable by left-handed people” — I’m left-handed, but habitually use my right hand for mouse/trackpad, and I know plenty of other left-handed people who do the same. – Peter LeFanu Lumsdaine Dec 6 at 12:00
  • 1
    @PeterLeFanuLumsdaine Likewise. I even remember that there was a period where I used the mouse left-handed as a child. I can't remember why I switched but I'm guessing it was just less hassle to develop a bit of ambidextry than to have to reconfigure every computer I sat down at. – ssokolow Dec 9 at 8:14
10

I am experimenting with a graphics pen and tablet and it got me thinking about the difference between it and my mouse. One huge difference is that the tablet's working area covers the whole screen,

No, that's scaling of your software. The tablet has its own coordinate set, which gets adjusted to your document and/or screen. Usually by the drawing application using it in absolute mode. For screen the driver may be configured to do it, or offer it as relative to fit usual mouse handling.

so that you can tap on an absolute position.

Jo. After all, with a tablet, the detection is not done by the moving device, but the fixed surface.

It's imperative for drawing tablets to work absolute, as for one there's no detected movement when the pen is (way) up. Only absolute detection will work to catch it when going down again. But more importantly, with a mouse a user usually 'homes in' to a target - meaning the movement is controlled via an optic feedback on the screen - while with a tablet the user expects to hit the point like with a pen on paper. No matter how much movement has happened in between.

My mouse always outputs relative x/y from its last position.

In general, without a fixed reference can only detect relative movement. Even a 'simple' device like an odometer only adds up data delivered as relative. And like everything working relative, it adds up errors. Thus relative recording isn't a great idea with tablets anyway, as the user assumes the device to read the exact spot he targets.

This is obviously a huge benefit because it does not restrict the mouse to one part of your desk.

The same can be done for tablets by scaling and panning. Take touch pads for example, here a cursor can be moved several times in one direction by repeated moves. Despite the fact that it delivers absolute coordinates. Similar is done for drawing tablets.

I am wondering if this was how the original mice/trackballs/whatevers did, or were they absolute position?

Always relative. Anything else would be incredibly complex and end up in a system resembling a drawing tablet. There have been combinations that looked like a mouse, but had to be used on a tablet (or with a fitting tablet like sensor setup), but they were incredibly expensive while combining disadvantages of mice and tablets.

For a generic, not very exact input device, relative is the way to go. Even more when the task is about relative positioning anyway.

  • "It's imperative for drawing tablets to work absolute, as for one there's no detected movement when the pen is (way) up. Only absolute detection will work to catch it when going down again." - What? Could you explain this further? It's not at all clear to me why absolute detection is required to resume tracking the stylus after it's left detection range. – 8bittree Dec 11 at 23:09
8

The Commodore 1351 mouse, created as an afterthought for the C64 and C128 and (ab-)using those systems' analog paddle inputs to transfer mouse position data (since no mouse support was planned when those computers were designed), maintains an internal sort-of-absolute position on a wrapping 64x64 pixel grid which it then provides to the computer. While mouse-supporting software running on those computers will have to convert those 64x64 grid positions to really absolute values by correcting for the wrapping and optionally applying some sort of acceleration algorithm, this type of mouse does not transfer relative position in terms of signed x/y displacement values.

  • It's interesting to note that the paddle inputs work by measuring how long it takes an external resistor to charge a capacitance, but the mouse works by waiting a precisely-controlled amount of time after it sees the capacitor discharged before it charges it essentially instantly. As such, it could achieve accuracy that's much better than such inputs should seem capable of supporting. – supercat Dec 6 at 21:20
6

As Stephan Kitts mentions, the mouse puts out relative coordinates. In reality the mouse sends its x/y movement (not coordinates) in mickeys (yes that's the name of the unit) to the PC in the form of interupts. The software can intercept these interupts and process them to do whatever: move a cursor, scroll, move an item in a game or more. Not necessarily anything to do with position on a screen. That is only a (now the most common) usage of a mouse.

1

When I was an older kid or early teen, my uncle took me to his office and let me play around on his computer. It was a dedicated CAD workstation, with a mouse that did actually encode absolute position on its pad (or whatever you would call it). The tail of the mouse was attached in the opposite position from modern mice, coming out under your wrist as you were holding it and plugging in to the "mouse pad" at the bottom, while a second cable connected the pad to the actual computer. At the top of the mouse, where the tail would normally connect, there was instead a crosshair that could be used to select icons that were actually printed on the "mouse pad" itself.

I remember getting frustrated because none of its four buttons were labelled, so you just had to remember which button did something with the mouse cursor on the screen, and which activated the function that the crosshair happened to be pointing at.

This is all from memory from quite a while ago, so I don't really have any more information about it, like a manufacturer or model or anything.

  • That sounds like a graphics tablet, very popular on CAD workstations. – bodgit Dec 6 at 16:45
  • @bodgit Yeah, it was very similar to a modern graphics tablet, except with a mouse instead of a pen or touchpad. – HiddenWindshield Dec 6 at 20:19
  • Most likely a Summagraphics or Calcomp tablet/digitizer, like this digitizerzone.com/calcomp-db6-sml.html – scruss Dec 9 at 14:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.