docking woes: navball parallax error

[Laie]

While assembling my Jool-5 mission, I hit a nasty snag pretty early: somehow, the game has trouble with my landers' main docking port. The port itself works, however, I have to align it visually: if I rely on the navball, I'll be off by a few meters.

Sorry about the lighting, but the key elements are visible. The target marker should be at least 20° off-center. Here's the rover during field trials (the port in question is below the lab, between the outriggers):

As you can see, there's a pod above one engine and a probe core above the other. The navball acts as if it was controlled from the probe core, or at any rate that's the offset I'm getting. You can believe me that I quintuple-checked which part I'm controlling from.

EDIT:

It seems that this is just how it is, at least for more complicated craft with ports on protruding bits. Only solution is to dock visually.

Edited July 15, 2014 by Laie

[Oafman]

I assume that if you set control from the probe it doesn't actually set your control as being from the docking port?!

I mean, it doesn't just have them switched around for some reason?

As a solution, you could just install one of the excellent docking mods, and ignore the navball. If you're not keen on using such aids, you could use it just for this instance where a bug is making non-modded docking very difficult.

[Alshain]

The pink marker indicates the heading directly toward the target, not the alignment of the port.

[Master Tao]

I assume that if you set control from the probe it doesn't actually set your control as being from the docking port?!

I mean, it doesn't just have them switched around for some reason?

As a solution, you could just install one of the excellent docking mods, and ignore the navball. If you're not keen on using such aids, you could use it just for this instance where a bug is making non-modded docking very difficult.

I use NavyFish's excellent and lightweight Docking Port Alignment Indicator, which automatically shows a list of all docking ports on your target once your within physics range. It can be a little counterintuitive if you don't watch the video first – you're moving the white crosshairs to the mark, not the other way around.

Many people prefer Romfarer's Lazor System Docking Cam, which shows a black-and-white view from the perspective of your docking port.

The pink marker indicates the heading directly toward the target, not the alignment of the port.

Specifically, the target's center of mass, which works well enough as long as the target docking port is aligned with it along two axes.

[Laie]

As a solution, you could just install one of the excellent docking mods, and ignore the navball. If you're not keen on using such aids, you could use it just for this instance where a bug is making non-modded docking very difficult.

Any suggestions? Though I somehow expect that they won't help. They need to get their assumptions about the docking port alignment from *somewhere*, after all. If they rely on the same source of information as the navball, they'd be just as wrong.

The pink marker indicates the heading directly toward the target, not the alignment of the port.

Does it look as if either port was pointed at the other?

[ArmchairGravy]

Do it visually is my recommendation. Navball only gives you info on 2 dimensions, and you need to use all 3. Also, putting the ports into North/South orientation (if you're in an equatorial orbit) will help.

Edited July 15, 2014 by ArmchairGravy

[Oafman]

Any suggestions?

Master Tao gave you the 2 popular options. I use the Lazor cam, because I think the video stream from the docking port looks cool. But Navyfish's mod looks excellent too.

Though I somehow expect that they won't help. They need to get their assumptions about the docking port alignment from *somewhere*, after all. If they rely on the same source of information as the navball, they'd be just as wrong.

Possibly. I hope not.

[Master Tao]

DPAI correctly gives your position and orientation based on the target docking port and the controlling docking port. I can usually set up docking with any port with this station from 1 km out, making slight corrections on the way in:

[Random Tank]

I love it when someone has a problem, loads of people say: add this mod to make it easier! It's a stock problem, and can be solved very easily in stock.

I've had this problem a couple of times, and I have no idea what causes it; fourtunately, this misalignment only becomes an issue when you get close to the target, (so I agree with ArmchairGravy) which at this point you can just dock by eye. Keep checking all 3 angle (up down, left right and forward backward) by rotating the camera; strafe is your friend, use the 'I J K L H and N' keys to strafe; also, I wouldn't recommend switching to docking mode, as this prevent you from controlling the crafts rotation, so just stick with staging mode. Keep practising docking by eye, and you'll get used to it in no time, without needing a docking mod!

[Alshain]

There is also Navball docking alignment indicator which helps a with rotation and direction but not actual alignment (left, right, up, down, in front of, or behind). It's more or less what your trying to do already. It's not as powerful as DPAI but I use it to find the initial direction of the port and then use DPAI to do the final maneuvers. Finding the orange ball on DPAI is a lot harder in my opinion.

Does it look as if either port was pointed at the other?

I really can't tell from that image. There is an optical illusion factor to consider.

Edited July 15, 2014 by Alshain

[Pecan]

Does it look as if either port was pointed at the other?

The target indicator actually points at the CoM of the target vehicle, not the targetted docking-port. Navyfish's Docking Alignment mod and the lightweight NavballDockingAlignmentIndicator (which I use but wish would get an abbreviation ^^) correct this and not only show you which WAY to point but which ORIENTATION you need - eg; you might need to MOVE right but FACE up, or some such.

HOWEVER:- While these correct for the position/rotation of the targetted docking port they do not correct for the offset of the controlled docking port from your CoM. IE; I have a tractor vehicle with docking-ports on outriggers some metres from the centreline - the indicator orientates me fine (facing) but tries to get me to dock the nose of the cockpit, instead of the docking port, into alignment. It is possible that this has been corrected in a later version than I'm using (hmm, doesn't seem to have a version number on it) - I'll be happy if someone knows if it has.

ETA for Alshain's post just above. I find the navball indicator alone sufficient because you still have the target position from the pink circle.

Edited July 15, 2014 by Pecan

[Master Tao]

... I wouldn't recommend switching to docking mode, as this prevent you from controlling the crafts rotation, so just stick with staging mode. Keep practising docking by eye, and you'll get used to it in no time, without needing a docking mod!

In docking mode, press the spacebar to switch between translation and rotation controls. I prefer to dock two handed, especially when visually docking, but that stopped being enjoyable for me with 20 m misalignments caused by the navball.

While these correct for the position/rotation of the targetted docking port they do not correct for the offset of the controlled docking port from your CoM.

As I posted on the previous page, DPAI does fix that problem. It correctly shows relative alignment to the target docking port, not the CoM.

[Pecan]

...As I posted on the previous page, DPAI does fix that problem. It correctly shows relative alignment to the target docking port, not the CoM.

And as I noted, while it corrects for the TARGET, it doesn't correct for the CONTROLLED ship.

ETA: for Master Tao below - ahh good. The NavballDockingAlignmentIndicator is derived from Navyfish's but doesn't make that adjustment. I may have to switch, which is a pity because I like the minimalism. Thanks for the information anyway.

Edited July 15, 2014 by Pecan

[Master Tao]

Sorry, I misread that part of your post. DPAI does also correct for the controlled ship – you just have to select "Control from Here" on your docking port; otherwise, it will be relative to your root part (usually the command pod).

[Lheim]

I'll pop in to say I've had the same issue with the inline clampotron part. I'll line things up perfectly by the navball, but be a meter or so offset in reality - almost as if it's using the end of the piece, instead of the docking port.

[EdFred]

Orrrrrrrrrrrr.....

Switch vessels, and control from here/set target on the docking ports in question, and rotate both craft to align them correctly. Where is it written that you can never rotate the vehicle being docked to?

[Laie]

I've had this problem a couple of times, and I have no idea what causes it;

Upon further investigation... it appears that the direction to target is always given relative to the root part of the ship (1). Which, in my case, is the Lab, which lines up nicely with the docking port, so it works fine. The first time. BUT: once I've docked and undocked, the game apparently picks a command module for a new root part. I've got several, but none of them line up with any docking port.

fourtunately, this misalignment only becomes an issue when you get close to the target, (so I agree with ArmchairGravy) which at this point you can just dock by eye.

As Alshain says, perspective can be a real spoilsport. I guess I'll try the docking cam.

(1) probably not quite the right way to put it. The general direction (whether it's forward, behind, or whatever) comes from where the docking port is pointed, but.. nah. Lacking words, I'll post a picture:

Target is the docking port on a stick. For the perspectively impaired, it's actually a bit behind the three forward-facing ports on the lander. I can control the lander from either of the three ports or the command seat and they all will tell me that the target is at (approx) 200°/-30° -- some ports are mounted upside-down, so they tell me the sky is below and the target marker is in the upper left rather than lower right. But it's still at 200/-30.

I've got corresponding ports on the other side. They tell me that they're pointed due north, and show a target_retrograde marker at 20/+30.

[Laie]

The target indicator actually points at the CoM of the target vehicle, not the targetted docking-port.

(Buzz sound) WRONG!

I refrain from posting more pictures, but the above setup has more than enough docking ports to pick as targets, I had the situation still open and could just do a few tests. It appears that the navball is correctly pointing TO the target, but it's not pointing FROM the port you're controlling with.

As long as your port and your root part line up, this works as intended. Not 100% sure about the root part, though -- it appears to be the root part when the vessel rolls out of the SPH/VAB; and some command module after the first undocking. Though for all I know, the game could completely restructure your ship upon undocking, so the command module may actually be the root part.

I'm reasonably sure that the CoM has no part in this. In my example picture, the lander CoM is slightly lower than the monoprop tanks. I wouldn't get a reading of 30 degrees down if it was based on CoM.

[Master Tao]

It appears that the navball is correctly pointing TO the target, but it's not pointing FROM the port you're controlling with.

As long as your port and your root part line up, this works as intended. Not 100% sure about the root part, though -- it appears to be the root part when the vessel rolls out of the SPH/VAB; and some command module after the first undocking. Though for all I know, the game could completely restructure your ship upon undocking, so the command module may actually be the root part.

I'm reasonably sure that the CoM has no part in this. In my example picture, the lander CoM is slightly lower than the monoprop tanks. I wouldn't get a reading of 30 degrees down if it was based on CoM.

Look at that – you answered your own question better than we did. Everything I've ever read here was that it was CoM offset, but it's the controlled ship's root part. Changing the controlling port changes orientation, but as if it were at the root part's location. Changing the targetted port works as expected.

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