What is the result of vector.direction ()?
Posted: Wed Jun 15, 2016 04:53I don't understand what's the result of vector.direction (p1,p2). Can someone explain this for me?
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What is the result of vector.direction ()?
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Posted: Wed Jun 15, 2016 04:53Re: What is the result of vector.direction ()?
Posted: Tue Jun 21, 2016 05:50Hmm, http://dev.minetest.net/vector doesn't have anything to say about it. Can you print p1 and p2 to console just to see what the values are?
Re: What is the result of vector.direction ()?
Posted: Tue Jun 21, 2016 06:05http://dev.minetest.net/vector doesn't have anything to say about it.
That is my problem
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print("Vector",dump(vector.direction({x=1,y=2,z=3},{x=4,y=5,z=6})))
Vector {
y = 0.11111111111111,
x = 0.11111111111111,
z = 0.11111111111111
}
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print("Vector",dump(vector.direction({x=1,y=1,z=1},{x=1,y=1,z=1})))
Vector {
y = nan,
x = nan,
z = nan
}
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print("Vector",dump(vector.direction({x=1,y=1,z=1},{x=2,y=2,z=2})))
Vector {
y = 1,
x = 1,
z = 1
}
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print("Vector",dump(vector.direction({x=5,y=3,z=4},{x=1,y=5,z=7})))
Vector {
y = 0.5,
x = -1,
z = 0.75
}
Posted: Tue Jun 21, 2016 09:20There's the code:
https://github.com/minetest/minetest/bl ... or.lua#L57
Obviously it firstly subtracts pos1 from pos2,
then it gets the abs values of the numbers
after that it divides every number by the biggest abs one, if there is not one biggest but two or three, it divides two or three times
l assume it's supposed to do the same as vector.normalize(vector.subtract(pos2, pos1))
but it does something completely different, it doesn't return a unit vector,
maybe it's supposed to return a vector with coordinates which are inside [-1;1] and at least one of them equal to -1 or 1
but this only works if each number's abs is different because there "if" is used and not "elseif", so if the numbers are e.g. {x=3,y=3,z=3}, instead of returning {x=1,y=1,z=1} it returns {x=1/3^2,y=1/3^2,z=1/3^2} (1/3^2 = 1/9 = 0.111…; see your test result) because it divides by the biggest abs number three times instead of just one time
l don't know what the result of vector.direction is good for…
https://github.com/minetest/minetest/bl ... or.lua#L57
Obviously it firstly subtracts pos1 from pos2,
then it gets the abs values of the numbers
after that it divides every number by the biggest abs one, if there is not one biggest but two or three, it divides two or three times
l assume it's supposed to do the same as vector.normalize(vector.subtract(pos2, pos1))
but it does something completely different, it doesn't return a unit vector,
maybe it's supposed to return a vector with coordinates which are inside [-1;1] and at least one of them equal to -1 or 1
but this only works if each number's abs is different because there "if" is used and not "elseif", so if the numbers are e.g. {x=3,y=3,z=3}, instead of returning {x=1,y=1,z=1} it returns {x=1/3^2,y=1/3^2,z=1/3^2} (1/3^2 = 1/9 = 0.111…; see your test result) because it divides by the biggest abs number three times instead of just one time
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print("Vector",dump(vector.direction({x=1,y=2,z=3},{x=4,y=5,z=6})))
print("Vector",dump(vector.direction({x=0,y=0,z=0},{x=3,y=3,z=3})))
print("Vector2",dump(vector.normalize{x=3,y=3,z=3}))
print("Vector2",dump{x=3/math.sqrt(3^2+3^2+3^2),y=3/math.sqrt(3^2+3^2+3^2),z=3/math.sqrt(3^2+3^2+3^2)})
print("Vector2",dump{x=1/math.sqrt(3),y=1/math.sqrt(3),z=1/math.sqrt(3)})
l don't know what the result of vector.direction is good for…
Re: What is the result of vector.direction ()?
Posted: Tue Jun 21, 2016 09:35duane uses this function in his valleys helper mod
it is also used in the identify mod
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local function calc_velocity(pos1, pos2, old_vel, power)
local vel = vector.direction(pos1, pos2)
vel = vector.normalize(vel)
vel = vector.multiply(vel, power)
-- Divide by distance
local dist = vector.distance(pos1, pos2)
dist = math.max(dist, 1)
vel = vector.divide(vel, dist)
-- Add old velocity
vel = vector.add(vel, old_vel)
return vel
end
it is also used in the identify mod
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local function node_contents_within_reach(center, direction, position)
local cluster = node_cuboids(center)
local i, j = box_distance_minimum(direction, position, cluster)
local reach = point_interval(node_ray_intersection(vector.direction(center, position), center), position)
local value = false
if not (i == 0) then
if (reach.x < 4.0) and (reach.y < 4.0) and (reach.z < 4.0) then
if (math.abs(vector.distance(box_side_intersection(direction, position, cluster[i], j), position)) < 5.0) then
value = true
end
end
elseif (i == 0) then
value = true
end
return value
end
Posted: Wed Jun 22, 2016 10:32l guess duane doesn't know what it does and isn't experienced with vectors
this should work better
or more streamlined:
lf l understand it correctly, the identify mod uses it for a ray iteration function, so a function which calculates positions which "follow" a line,
the technic mining laser uses a ray iteration function,
as far as l know there are lots of ways to do such a rayIter function and lots of bad and wrong working ways,
l made one myself (https://github.com/HybridDog/vector_ext ... t.lua#L100), it's fairly simple but it tests each (of the 3 or less) position if it fits best, so it's not perfect
this should work better
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local function calc_velocity(pos1, pos2, old_vel, power)
local vel = vector.subtract(pos2, pos1)
vel = vector.normalize(vel)
vel = vector.multiply(vel, power)
[…]
or more streamlined:
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local function calc_velocity(pos1, pos2, old_vel, power)
local vel = vector.subtract(pos2, pos1)
vel = vector.multiply(vel, power / vector.length(vel))
[…]
lf l understand it correctly, the identify mod uses it for a ray iteration function, so a function which calculates positions which "follow" a line,
the technic mining laser uses a ray iteration function,
as far as l know there are lots of ways to do such a rayIter function and lots of bad and wrong working ways,
l made one myself (https://github.com/HybridDog/vector_ext ... t.lua#L100), it's fairly simple but it tests each (of the 3 or less) position if it fits best, so it's not perfect
Re: What is the result of vector.direction ()?
Posted: Wed Jun 22, 2016 16:03Whatever this function does, it doesn't look like it calculates a direction. In linear algebra, a direction is usually:
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normalise(to - from)
where
normalise(A) = A / |A|
Posted: Thu Jun 23, 2016 17:10rubenwardy, so a "direction" is always a unit vector?
And the direction from pos to pos (resulting in the zero vector) is an isotropic vector?
And the direction from pos to pos (resulting in the zero vector) is an isotropic vector?
Re: What is the result of vector.direction ()?
Posted: Fri Jul 15, 2016 17:37I'm not sure, but I think this function calculates a vector between two positions
Re: What is the result of vector.direction ()?
Posted: Fri Jul 15, 2016 19:40burli wrote:I'm not sure, but I think this function calculates a vector between two positions
I don't think so, for that you only need to subtract the initial position from the final position, vector.subtract(b, a) would return the vector from point a to point b.
Just as Hybrid Dog and Ruberwardy said, the unitary vector between two points would simply be:
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function vector.direction(a, b)
return vector.normalize(vector.subtract(b, a))
end
And if instead of 2 points you have 2 vectors that you want to merge into one to get the resulting direction when combined, you would rather just use vector.add and then (if needed) normalize it.
Posted: Sat Jul 16, 2016 07:33