hebarusan / laserdist

KSP Part that measures straight line distances by laser

LaserDist

[WIP, Plugin, Parts] LaserDist 0.9 for KSP 1.1.2

Releases:

• https://github.com/Dunbaratu/LaserDist/releases

ZIP Download (See release page above):

Source Code Hosting site:

• https://github.com/Dunbaratu/LaserDist

License:

• GPL v3

Copyright (C) 2014,2015,2016 Steven Mading (aka Dunbaratu on Github) [email protected]

This is a very small plugin. It makes a KSP Part that measures straight line distances by laser.

This module ships with 3 different models of Laser:

100x model

The "Beamer 100x Disto-o-meter" Part aims a laser in a line and then measures the distance in meters to the first object the laser hits. The result is displayed in the right-click menu for the part and can be read by kOS (and other?) script mods.

The direction of the laser is whichever way the laser gun is pointed when you mounted it on the craft, as demonstrated here:

200x model

The "Beamer 200x Bendable Disto-o-meter" Part is the same as the 100x part described above, but it lets you choose a deflection angle with the "Bend X" widget on the slider, (or by using SETFIELD in kOS on it), and the laser can dynamically change it's aim along this one axis.

500x model

The "Beamer 500x Aimable Disto-o-meter" Part is the same as the 200x part described above, but it lets you bend the laser in two different axes, to aim it whereever you like within a zone, using both "Bend X" and "Bend Y" settings.

All models:

The laser can work over long distances - here it's measuring the distance from a Kerbin orbit vessel to the Mun:

And even at those very long distances, the lasers can measure rather small differences in distace, within reason (it has an accuracy of 2 meters at this extreme range, to keep the game from bogging down too much). In the screenshot below, notice how the two lasers are returning different numbers for their distance to the terrain very far away:

The electric draw for the laser is substantial. Each laser consumes 1 electric charge every 3 seconds that it's on.

Why does this Mod exist?

The intended purpose of this part is to be used in conjunction with scripted autopilots like kOS, to provide a way to for you to write scripted pilot software that can see the distance to the ground (or anything else like a ship) along the laser line. The reason this can be useful is so you can detect things like terrain slope and mountains in the way. The default radar altimiter in KSP only shows you the distance directly under the craft.

In a nutshell, the purpose is to solve this problem:

This mod can let you read the distance along the blue line in the diagram.

Why isn't it inside kOS then?

There is more than one KSP mod project for the purpose of letting users write scripted autopilots. Another such project currently under development is Jebnix.

My goal is to make this part script-engine-agnostic so it works with any such mod. I've been working in kOS mostly, but I didn't want this part to be kOS-specific because there's no particular reason it has to be.

Information about the data fields the part displays:

• KSPField: 'Distance' is a float - the number of meters being shown in the display. It's -1 if there is currently no hit.
• KSPField: 'Hit' is a string - the name of the object being hit.
• KSPField: 'Activated' is a bool - true if the measuring device is on.
• KSPField: 'DrawLaser' is a bool (called "Visible" in the GUI) - true if the laser should be drawn when it's activated or false if it should be (realistically) invisible because, hey, it's coherent light and it's not supposed to be seen from the side.
• KSPField: 'CPUGreedyPercent' is a float (called "CPU hog" in the GUI) ranging from 0.0 to 20.0. It's how much of a single physics tick of time this mod will allow itself to consume during a single Update. If it hasn't gotten a good enough answer within that much time, it will wait until the next update to continue the calculation.
• KSPField: 'UpdateAge' is an integer - It's how many Unity Updates (animation frames, basically) it's been since the value you are seeing was calculated. Becuase of the logic of CPUGreedyPercent (see above) sometimes the value being displayed is stale by a few update ticks and shouldn't be trusted until the next time that UpdateAge becomes zero again. If you're in a situation where this mod needs to spend more than 1 update of time to get to a good answer for the distance, you'll see this value spinning a bit, quickly going 0,1,2,3,0,1,2,3,0,1,2,3...etc. When you see that, only when it hit the zeros was the distance value perfectly correct at THAT moment.
• KSPField: 'Bend X' is a float - the number of degrees the laser is deflected in its relative Yaw direction, if it's the type of laser that can be deflected.
• KSPField: 'Bend Y' is a float - the number of degrees the laser is deflected in its relative Pitch direction, if it's the type of laser that can be deflected.
• KSPField: 'Max Bend X' is a float - the range of bending the laser can do in its relative Yaw direction. If this is zero, then the laser cannot bend that way. The range is always centered at zero, plus or minus this number.
• KSPField: 'Max Bend Y' is a float - the range of bending the laser can do in its relative Pitch direction. If this is zero, then the laser cannot bend that way. The range is always centered at zero, plus or minus this number.

Note: The higher that CPUGreedyPercent ("CPU hog") is, the less likely it is that UpdateAge will ever be nonzero, but the bigger hit your framerate might take.

How to Mount it.

. The Beamer 100x Dist-o-Meter is located in the "Electronics" tech node of the career tech tree. It's a 300-point node on the tree so you might not have it yet in a new fresh career game.

The Laser can be mounted anywhere as a surface-mount item. Take care to note the orientation of the laser emiiter. (KSP lets you fine-tune the rotation of a part by using the SHIFT key while you hit the WASDQE keys.)

The Laser will bounce back and give you a distance measurement when it encounters ANY object, including parts of your own craft. So take care to mount it somewhere where the laser beam will have a clear line of sight without obstruction.

To ensure a good mounting point, you can use "tweakables" to enable the laser and make it show up in the VAB to look and see if you have it aimed well.

Lightspeed

Note that if you use it to measure the distance to a far away body (i.e. like aiming it at Duna from Kerbin), the mod does take into account lightspeed. You have to hold the laser on an object steady and unchanged for the entire duration of time it takes for lightspeed delay to bounce the signal back or you won't get a measurement, so using it at that great distance will be very hard.

FUTURE EXPANSION PLANS (i.e. the reason this is a WIP)

Max distance isn't enforced yet: It's part of a future plan to have different variants of the part that work better the higher up the tech tree you go. For now, despite what it says, the range is actually infinite.

Other sorts of sensors?: Now that the numerical approximation behind making a "fake raycast" that finds intersections with the planet terrain from far away and from any angle is implemented, this opens up the chance that other sorts of long range beam sensors could be made. For example a "biome detector" that returns the name of the biome where the hit occurred is a possibility, as is a "density at a distance" measurement which might tell you the atmospheric pressure or density at the ground level where the hit occurred. (Maybe because of something that the laser detects about interference with the air? It's a bit hard to justify realistically how that would work, but it's definitely possible with the software. Just not sure if it's possible in the real world, or whether real-world sanity is really the intent of this mod or not.

How do I use it from my script then?

Quick synopsis:

Getting a handle on the laser, then turning on the laser using that module:

SET laser_module TO SHIP:MODULESNAMED("LaserDistModule")[0].
IF not laser_module:GETFIELD("Enabled") {
  laser_module:SETFIELD("Enabled",true).
}

Getting a reading from the laser:

SET laser_module TO SHIP:MODULESNAMED("LaserDistModule")[0].
PRINT "Laser distance is measuring " + laser_module:GETFIELD("Distance") + " meters."
PRINT "Laser is hitting: " + laser_module:GETFIELD("Hit").

Transforming the laser reading into a 3-D coord:

The part model is designed such that emitter of the laser line is located exactly at the part's local transform origin position, aimed along the part's facing:vector unit vector, allowing you to get its 3D vector position from a script like so, Provided you haven't bent the laser with the "Bend X" or "Bend Y" settings. If you have bent the laser, then you need to apply these offset angles yourself with an ANGLEAXIS rotation in kOS :

SET laser_module TO SHIP:MODULESNAMED("LaserDistModule")[0].
set dist to laser_module:GETFIELD("Distance").
set emitter_position to laser_module:part:position.
set emitter_unit_vec to laser_module:part:facing:vector.
set laser_hit_position to emitter_position + (dist * emitter_unit_vec).

// laser_hit_position is now a 3D vector position of where the laser hit something.

// To do the same general thing but when the Bend X and Bend Y fields are nonzero, // rotate the vector around the part's facing unit vectors:

SET laser_module TO SHIP:MODULESNAMED("LaserDistModule")[0].
set dist to laser_module:GETFIELD("Distance").
set emitter_position to laser_module:part:position.
set emitter_center_vec to laser_module:part:facing:vector.
set x_bend to laser_module:GETFIELD("Bend X").
set y_bend to laser_module:GETFIELD("Bend Y").
set bending_rotation to
      angleaxis(x_bend, laser_module:part:facing:topvector) *
      angleaxis(y_bend, laser_module:part:facing:starvector).
set emitter_unit_vec to 
      bending_rotation * emitter_center_vec.
set laser_hit_position to emitter_position + (dist * emitter_unit_vec).

### Part modeling help?

I am aware that the artwork on the models aren't pretty.  I'm a 
programmer, not a graphic artist, and I don't have experience
with things like Maya and Blender.  In fact I just made the model
by slapping together some stretched Cube and Cylnder objects in
Unity itself, without the aid of a modeling program.  The model
is good enough to work with, but I'd be happy to have someone
better at art redesign the model.  I included the model in
the github directory if you want to have a look.