I'm lost in translation

[Shaggy Hiker]

It's late and I'm tired, so this may prove to be a D'OH kind of a question, but here it is (and yes, it's related to something I started on a couple months back):

If I have an object at the origin with a heading of H, and I have a bearing B and a distance D to a different object N, how do I get the x,y coordinates of that other object. I see a way to do it by figuring out which quadrant N is in, and doing the trig depending on that quadrant. That's really not all that difficult, but I was thinking there might be something slicker than a series of If statements to figure the quadrant, then a bit of trig.

[opus]

If you have the bearing in 360 degrees and the position in two Single vars (not in degrees and minutes, X increases to the right/East, Y increases to the top/North) you can use this:

Public Point_Type
  X as Single
  Y as Single
End Type

Public Const PIDiv180= 3.14159265358979/180

Public Function EndPoint (StartPoint as Point_Type, Bearing as Single, Distance as Single) as Point_Type
EndPoint.X = Sin(Bearing*PIDiv180)*Distance+StartPoint.X 
EndPoint.Y= Cos(Bearing*PIDiv180)*Distance+StartPoint.Y 
End Function

[zaza]

If you're at the origin, then your coordinates have no impact on those of the object N. All that matters is your heading.

Since the relative bearing is B and your heading is H, then the actual bearing of N relative to 0^o (i.e. due East) is just B + H (mod 360, and assuming that there is a proper 360 degree or negative convention). If your bearing is taken from a different point, just include the offset from your "local" 0^o as a constant, e.g. if bearing is from "straight ahead", then add on 90^o.

Now that you've got the angle from 0^o (true East) and the distance from the origin, you just want the sin and cos to get x and y.

zaza

[opus]

Hi zaza, did I miss something, as far as I undeerstood B stands for bearing and not relative bearing!
Also I have to state that my code goes for bearings 0 to 360 degrees, where 0 is North and 90 is East!!!

BTW: I'm an old fashioned airborne-navigator, I was trained using an sextant to shoot the stars and using Loran, so please don't make me change this habbit!

[zaza]

My understanding is that bearing is with respect to the direction in which you are travelling, hence you need to account for heading. I normally take coordinates and angles with respect to the x-axis, which is why I included the bit about accounting for your "local" 0^o.

Shaggy's a smart bloke though, I'm sure he already knows all this.

[opus]

I normally take coordinates and angles with respect to the x-axis, which is why I included the bit about accounting for your "local" 0o.

Note that you probably count from 0 (east) to 90 (north), whereas I'm counting from 0 (north) to 90 (east), which is the otherway around! (I had to learn this kind of "false" directions the hard way at a time!)

Shaggy's a smart bloke though, I'm sure he already knows all this.

I know that, I've read enough of his post's.
It's always a pleasure to help (or to try to help) one of the guru's of this forum!

BTW. What's the meaning of "D'OH"?

[zaza]

Note that you probably count from 0 (east) to 90 (north), whereas I'm counting from 0 (north) to 90 (east), which is the otherway around! (I had to learn this kind of "false" directions the hard way at a time!)

Correct, but to be honest that's only a fixed 90 degree offset. It doesn't require any more complex a calculation.

BTW. What's the meaning of "D'OH"?

Ask Homer Simpson.

[Shaggy Hiker]

Man, I'm tired. I really want to get back to this.....but I can't for a couple of days. You both made good points, however, here's my perspective on it: I'm an old navigator, too, but map and compass on ground work, so 0 is North, and 90 is east for me, as well. Also, this is my robot project, and the robot has a compass, so 0 will generally be north.

However, to wander off onto a totally irrelevant tangent, I am wondering how well my navigation will even work (I hope to find out in the next month). The compass is a sensitive electronic one. I will have to be watching to see whether things like the refrigerator cause my perceived heading to begin veering. It would be interesting to make a map of magnetic deviation around the house, but it will be a heckuva challenge doing navigation if every sensor has variable, non-random, error over the course of a straight line. I'm fairly eager to find out whether this will be a problem, but right now I'm still throwing a track whenever I turn a corner. More parts in the mail, might have a workable solution this weekend. Pictures in a month or so.

Then getting back to the topic at hand:
In this case, I do have only a relative bearing (and a true heading), but converting that to an absolute bearing in my 0 degrees N frame of reference is pretty simple math.

Yeah, it turns out it is a D'OH moment, and yes, that is a Homer Simpsonism. I think I'm no less sleepy now than I was when I wrote that first post, but even as fogged as I am I realize that once I get the true bearing the position of the point is simple.

By the way, I think there is already a Point structure tucked somewhere into .NET. I may find it, or I may not bother. In any event, I will be doing everything in integers ultimately, because the error in all of my measurements is such that even a single decimal place is pseudo-precision.

Thanks for the help, though, it was useful to me.