WIP: [core] Add a unidirectional Perlin Ground HeightmapFunction #799

mwulfman · 2024-05-17T16:13:21Z

I am proposing to add a unidirection Perlin ground HeightmapFunction, 2D Perlin ground HeightmapFunction and a quantization methods to quantize any ground to certain z-values.

Unidirectional Perlin Ground:

2D Perlin Ground

Pass the Perlin process by copy to the builder function
Ground quantization method to quantized the ground to only certain level
Unit tests
Fix sample_state in gym-jiminy to account for the ground profile ?

core/src/utilities/random.cc

core/include/jiminy/core/utilities/random.h

duburcqa · 2024-05-17T16:27:04Z

It would be nice to add a quantization options to quantized the ground to only certain level.

What do you mean ?

mwulfman · 2024-05-17T16:32:47Z

It would be nice to add a quantization options to quantized the ground to only certain level.

What do you mean ?

To be able to get this type of terrain:
(ref: https://fse.studenttheses.ub.rug.nl/30171/1/thesis.pdf)

duburcqa · 2024-05-17T18:59:00Z

I see. It looks like a quantisation based on the vertical value only. Something like z = std::floor(z / delta) * delta. The issue is that we still need to add small slopes...

I think tiles or tile2dInterp1d should be extended to support "tile-ization" of any ground profile. The advantage is that it does not require having access to the normal of the original ground profile !

duburcqa · 2024-06-04T09:42:17Z

Are you planning to work on it ? If not, then I suggest closing this issue because I'm not planning to work on it either.

mwulfman · 2024-06-04T09:46:27Z

Yes, I did a bit more work on it but didn’t push anything yet. I’m planning to work on/finish it in a couple of weeks.

duburcqa · 2024-06-04T09:49:35Z

Ok perfect ! Let's keep it open then :)

duburcqa · 2024-06-14T07:49:23Z

Apparently you made good progress ! Nice :)

What is your future plan ? You want to add quantisation ? Can you add a unit test checking if the gradient is right ?

core/src/utilities/random.cc

duburcqa · 2024-06-15T05:55:45Z

leads to floating point exception (core dumped)

The problem is not that it asserts to false because asserts are disabled for release build type. The issue is rather the contrary, we should systematically check this condition and raise an exception if not satisfying this condition causes segfault.

I will issue a fix for this.

mwulfman · 2024-06-15T10:40:19Z

Apparently you made good progress ! Nice :)

What is your future plan ? You want to add quantisation ? Can you add a unit test checking if the gradient is right ?

Yes, I still need to do :

some update of the code (following your comments as well),
add quantisation on any ground,
since I'm already into Perlin noise, I'm thinking of adding 2d perlin noise/ground
Yes, add unit test for the gradient. I was thinking of comparing the gradient with the numerical gradient, were you thinking of any other tests?
Maybe update sample_state in gym-jiminy to account for the HeightMap.

duburcqa · 2024-06-15T10:44:35Z

I was thinking of comparing the gradient with the numerical gradient, were you thinking of any other tests?

Nope it is fine :)

Maybe update sample_state in gym-jiminy to account for the HeightMap.

I'm afraid doing this is not straightforward. It has been a long-lasting issue as you know. Once everything else is working, I could help you on this part to improve the current heuristic that has not sufficient in many cases.

…in process

…tion

duburcqa · 2024-07-08T06:42:16Z

core/src/utilities/random.cc

+        return (yRight - yLeft) * dRatio + lerp(ratio, yLeft / dtLeft, yRight / dtRight);
+    }
+
+    double AbstractPerlinNoiseOctave::operator()(double x, double y) const


I don't understand why do you need all. 2D Perlin process is not the same as the sum of 1D processes along x-axis and y-axis respectively ? If so, just do this.

2D Perlin process is not the same as the sum of 1D processes along x-axis and y-axis. Here's a photo of the sum (to compare with the photo in the description). That's what I did first and then realized quickly it wasn't what I was looking for.

Ok now I see the issue. It is indeed more tricky than expected at first glance. I'm going to think about it to see if there is a way to get the same result without duplicating everything. The big issue is that the contribution of each process independent on each axis.

I'm wondering if passing the 2D position encoding (hash) to two independent random processes should do the trick. I will try that.

After check, it is indeed more tricky than that and you really need a 2D implementation. Position encoding is not enough per se. I forgot about random Perlin processes were evaluated in the first place. Since it is an interpolation, it is always necessary to have a dedicated 2D implementation.

duburcqa · 2024-07-08T06:45:17Z

core/src/utilities/random.cc

+
+    template<typename PerlinProcessType>
+    void computePerlinHeightmap(PerlinProcessType perlinProcess,


Just make this signature more general to support specifying pairs (axis, PerlinProcess), this way:

template<typename PerlinProcessType, int N> void computePerlinHeightmap(std::array<std::pair<Eigen::Vector3, PerlinProcessType>, N> perlinProcesses, ...

Then all you have to do is to project the current pose only each axes and aggregate the result. You can do this automatically using sumHeightmaps, which has been designed for this exact purpose.

Like shown in the photo above, I don't think that's what we want.

duburcqa · 2024-07-08T06:48:19Z

To many code duplication. There should be no need to implement anything specific for the 2D scenario.

duburcqa · 2024-07-08T07:08:58Z

I'm going to help you on this, so that we can close this long-lasting PR.

mwulfman · 2024-07-08T07:20:08Z

I'm going to help you on this, so that we can close this long-lasting PR.

If you have time for it, I'm pretty happy to get your help. I didn't have much time to work on it the last few weeks, but hoping to finish it this week.

duburcqa · 2024-07-08T07:31:47Z

core/src/utilities/random.cc

+
+        // Constant for avoiding discontinuity at (0.0, 0.0)
+        const double offset = 100.0;


What is this ?

It's a non-ideal fix. Since the 1d perlin process is defined only on t >0, I needed a way to have it well defined for t<0 as well. Using the absolute value of t doesn't work since you end up with a discontinuity at t=0. So instead I shifted the perlin process by a offset. But it doesn't change the fact that the perlin process remains undefined for t < offset.

Ok I will check if it can be refactored to work with negative values.

duburcqa · 2024-07-08T07:50:33Z

core/src/utilities/random.cc

+    {
+        // Compute random gradient
+        // Get knot
+        uint64_t knot = (static_cast<uint64_t>(ix) << 32) | static_cast<uint32_t>(iy);


I'm not convinced by this. The periodicity is supposed to have the spatial interpretation in physical world. A repeating pattern is supposed to be clearly visible. I'm wondering what it looks like in this case. In the case of periodic Perlin noise, I have the feeling that sumHeightmaps is the way to go. Anyway, I don't think it really makes sense for ground profile generation.

One option would be to do:

uint32_t deltaPeriod = static_cast<uint32_t>(period_ / wavelength_) ix %= deltaPeriod; iy %= deltaPeriod; uint64_t knot = (static_cast<uint64_t>(ix) << 32) | static_cast<uint32_t>(iy); const double s = perm_[knot] / 256.0;

By the way, I think there was an issue in the 1D case if deltaPeriod > 256

duburcqa · 2024-07-08T13:14:20Z

Ok I skimmed through the code. Now I remember. Since those processes at not used for anything inside core itself, I'm going to refactor them a bit. In particular to replace operator() by evaluate and add evaluate_gradient which will return both the value and its gradient. Some internal methods also need a better name, such as grad that is confusing now. Then, I will rather template them with the dimensionality of the process, with only 1 and 2 being supported at the moment. I hope this will make everything more simple and clear, while avoid redundancy.

mwulfman · 2024-07-09T22:20:28Z

Since you're taking over for the PerlinNoise part, I started creating some unit tests (using the current methods' name) and fixed a typo in the 1D gradient computation. There is also a bug in the 2D gradient computation.

duburcqa reviewed May 17, 2024

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duburcqa reviewed May 17, 2024

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duburcqa force-pushed the dev branch from f49f6b9 to 8ff3ac6 Compare May 24, 2024 14:59

mwulfman force-pushed the perlin-ground branch 2 times, most recently from 5167e9f to 75575c6 Compare June 13, 2024 22:04

duburcqa reviewed Jun 15, 2024

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duburcqa force-pushed the dev branch from 1eef2b4 to 78d0195 Compare June 19, 2024 07:01

mwulfman added 7 commits July 3, 2024 22:47

rebase

4610917

numerical fix stairs

067131e

🔨 adding gradient computation method for perlin noise octave and perl…

d7b6ac5

…in process

🔨 restore constant position offset for now

88b4001

💄 format cc

3783371

add and update boost signature

3fd5dd3

fix line spacing

44acb37

mwulfman force-pushed the perlin-ground branch from cc275e3 to 44acb37 Compare July 3, 2024 20:48

mwulfman added 5 commits July 3, 2024 23:15

🔨 use function and not lambda for the heightmap

f736b25

:lisptick: format random.cc

1b7fd6c

🔨 add 2d support of perlin noise

039250e

⚡ add 2D perlin ground

35df589

fix format

8c2a552

Instanciate the Perlin process once, at creation of the heightMapFunc…

07f4b04

…tion

duburcqa reviewed Jul 8, 2024

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Add tests that are not all passing for now

f9884e5

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WIP: [core] Add a unidirectional Perlin Ground HeightmapFunction #799

WIP: [core] Add a unidirectional Perlin Ground HeightmapFunction #799

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mwulfman commented Jul 9, 2024


		template<typename PerlinProcessType>
		void computePerlinHeightmap(PerlinProcessType perlinProcess,


		// Constant for avoiding discontinuity at (0.0, 0.0)
		const double offset = 100.0;

WIP: [core] Add a unidirectional Perlin Ground HeightmapFunction #799

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WIP: [core] Add a unidirectional Perlin Ground HeightmapFunction #799

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