Surface or mesh over self made sparse point cloud...how?


#1

Hi,
V4 and V5,

I have a compound curve shape brought in from a photogrammetry prog where I have had to make my own sort of point cloud, selecting marks on this surface and creating markers/points for them, so not exactly a cloud of them !!!. see attached.
I hope to get Rhino to place a surface or mesh through these points. Surface ideally as I am familiar with surfaces and solids etc . I did this without even checking that such was possible. Had no other choice anyway. No internal frames to follow, just a shape with some spatter on it I could use to orient photos and used rthe spatter spots as my point cloud points !

What command do I use to place a curvaceous compound curve type surface through my sort of point cloud, and unlike CAD generated point clouds, my points are very sparse, density varying. The file is attached.

How do I limit the extent of the surface ? I have curves I would like it to end at. As you can see they dont all join up, again it was what was possible in the photogrammetry. I have added points to some lines that ran across the surface to give further accuracy.

I need the method ideally for V4 though if its only possible with V5 then it will mean spending time altering V5 interface, have to do it sometime I guess but not when against the clock as I am at the moment !

SteveShroud_Pmodeler.3dm (83.5 KB)


#2

I imagine Patch would be one solution…

–Mitch


#3

Hi,
sounds promising, but trying default then stabbing around altering figures and settings without fully understanding what they do, though its one way to find out, the stretched jellyfish I get is nothing like my hoped for shape with a surface between its points. Light years away.

I closed the gap at toe front but it made no difference. It would seem though a prerequisite to have a closed shape to patch into.

Steve.


(David Cockey) #4

Not a simple ask. My approach would be to:

  1. Create an approximate four sided boundary.
  2. Create one or two approximate internal curves between opposite boundary curves.
  3. Use the approximate curves to create a “starting surface” for Patch
  4. Rebuild the starting surface with the smallest number of points in each direction which might be needed to capture the shape.
  5. Use Patch with the starting surface option and the data points and curves…
  6. Use PointDeviation to see how close the surface is to the data points and curves, and where the largest deviations are.
  7. Experiment and iterate with the shape of approximate curves, the number of control points in each direction in the starting surface, and Patch parameters to improve the surface from Patch. I usually start with a sparse starting surface, and then insert rows/columns of points in areas with high curvature…
  8. Trim the surface from Patch as needed.

I would estimate it would take me several hours to get a good surface using the data you have.


(David Cockey) #5

Several other comments.

Depending on the photos you may be able to get a much denser point cloud with PhotoScan. Standard version is $179 in the US.

If you do this again with PhotoModeler put targets on the surface arranged in a network of curves.


#6

Hi David,
several hours…strewth, thats game over, and very bad news for me…and those steps…eeek !

Not sure I understand some of them, like internal curves.

The site visit disallows targets and markers. Museum aircraft and sticky spots …a no no ! The photos had to be done in under 5 mins ! Permission limit. It was one photo every 10 secs. Really lucky to find minute spots on it in some places.

If I had stuck sticky spots over that shape, would rhino then have handled it, or would then photomodeler have handled it ?
With the steps you mention it seems Rhino simply hasnt a command to handle a point cloud, let alone a sparse user created one.

Is it that a CAD generated point cloud Rhion would understand, but a user created one it cant ?

With RAD markers to assist, Photomodeler might have automated the task though such must not bend else are not recognised, I gather.

The photos were tried in Pmodeler scanner by EOS, they failed, not enough texture, but real world subjects dont meet with their ideal rules.

Looking at the points I had hoped and assumed that Rhino being nurbs and this right up its street, would have a simple command that ran a surface through those points, with options to vary the effect incase it looked like the ocean with points in the troughs, or likewise with points on the peaks of the waves. A nice smooth best fit surface ending at the edge lines. I obviously need to close the shapes, ie that hole at the front.

I have spent days and days matching specks across photos to give a point type surface for Rhino to surface.

Steve


#7

I don’t think your data is good enough for a good fit plus a smooth surface, so I just put a smoothish patchlike thing through the points knowing that it will miss a number by a good distance. I didn’t include the curves, I added a few points along the bottom edge. Attached is my 5 minute try.

I’m sure you can do much better, but that’s all I had time for. You would of course need to tweak and trim it afterward. If you use more spans and/or lower stiffness, you will get a surface that is closer to the points but has more wrinkles and will be harder to edit. I don’t know what your goal is here.

–Mitch

ShroudPatch.3dm (423.1 KB)


#8

Hi,
Thats not at all bad !
This has given me new hope.

Just need to come out a little up at the top for the two ‘winglets’ to give them some name.

I need to know the steps involved.

5 mins would be capture on techsmith Jing by the way, dead easy free screen capture some Rhino users are using.
What a difference seeing something happen capturing the inputs and other moves made, not sure about keyboard input though.

Just what are the steps please ?

Did you first draw the blue rectangle surface sheet ?

what is the purpose of this blue surface rectangle by the way ?

You used the patch command I assume.

How best should I trim it, do I use side view and use trim command ?
I cant select my outline shape of it to do that, yet layer is not locked. Its all on one layer, I am baffled here.

if the port side is different shape from the stbd side, a top view trim would no doubt be better.

Attached jpg my goal, the metal shape I need to create in Rhino as a surface or mesh, to then be able to create othographic views of it, to draw up plans of the subject it is part of. Furthermore to be able to add it to the part completed 3D Rhino model of that bigger subject. I need to understand and capture its compound curves, not just get a side view of it. and maybe send it for milling to create a plug over which sheet will be placed to recreate its shape.

Photomodeler has no tools to surface the user created points as in this, they say a prog such as Rhino will do so.

Steve


#9

First have a look at the help for the Patch command so you get an idea what the parameters do.

Basically it’s balancing the number of spans in each direction with the stiffness control. You need to play with the different values to see what they do. Each situation will be different, so it’s a trial-and-error process.

  1. The more spans there are, the more it can flex locally to fit your input - but at the expense of a heavier and harder to edit surface and one that might have more local bumps.

  2. The higher the stiffness setting, the more “tension” you’re pulling on the surface, it will be smoother, but may miss more points.

The starting surface can be used in a number of ways. In this case, with Pull=0, it is just used to force the alignment of the UV spans of the Patch - they will match the UV of the starting surface. What you’re doing is giving Patch a clue as to how you want the surface constructed. Without this it will often do some random thing with confusing data like yours (try it). I found that a surface oriented at 45° may be better to try to match the point set. In this case the surface is just a simple plane a bit bigger then the point data, but it can be any kind of surface.

In your file I also added some additional points to help guide the outer edges of the patch. I did not use the curves. The result still is not all that smooth, but it’s just a starting point.

To get a better result, one could construct a second-generation surface by perhaps extracting the isocurves of the Patch surface in one direction, rebuild/edit them, then run a new surface through the curves with Loft. That would most likely would give a better quality and more controllable result. Assuming it’s supposed to be symmetric, I might find a suitable mid-line, do only half the curves and then mirror it.

There’s obviously a lot to take in and understand here, but that’s what acquiring experience is all about - this kind of situation cannot be solved with a “cookbook” approach.

Good luck,
–Mitch


#10

Hi Mitch,
MANY THANKS INDEED :slight_smile:
the video is everything…so useful. MANY THANKS FOR THIS AND FOLLOWING MY HOPE FOR SUCH…BEST THING TO HAPPEN TODAY. VIDS SO USEFUL. I watched it several times picking up on minor things that all help.

Attached my stab at this. I tried for planar surface and also similar shape as CommandHelp says.

Q1) IS THERE A WAY OF SELECTING POINTS THAT ITS MISSING IN AN OTHERWISE PERFECT FIT AND GETTING IT TO REVISE ITS SHAPE IN THEIR LOCALITY ? 45deg surface is winning but for a couple of lines .

Q2) Whilst points are selected its difficult to see what is inside and outside. Once OK is clicked then the inside points are easy to see. Is there a way of it showing points inside and points outside the patch when they are selected during preview as its here when we ned to see how its fitting, and in shaded view it seems its in ghosted view !!!

I tried the 45 deg planar surface, its not bad, just a tad fat at lower rear. The leading edge needs to be a little more rounded, its based on an aerofoil .

I then read in the commandHelp that a startsurface similar to the final required shape is good to do,

To get this, in a side view I drag a thin selection box across selecting a number of points, SetPt flatten them to X and InterpCrv draw through them and get a fair idea of the aerofoil. Smooth it out a bit.
Sweep this to the leading edge line and position it inside the points, but it cannot pull the patch outward enough, the bottom edge curves are clear of patch.

I try again with it scaled larger and sitting outside the points. It fails to have the desired effect and doesnt see the lower edge correspond despite altering pull value.

I then take the true aerofoil section and sweep1rail placing it ouside the points, again the lower edge doesnt fit the patch.

Seemed like a darn good idea but it doesnt work so well. U and V values greyed out as well for the aerofoil section StartSrf. denies more control…why is that ?

It seems the planar surface rectangle is better than CommandHelps idea of a similar shape !

I need to understand the effects of its angle and placement more. Your level one also looks good.

i feel we need a few more options, like select points to locally alter shape, as altering the values spoils it elsewhere when trying to bring a few important edges into touch the patch.

This patch command is a good one in theory, wish it had been developed further still since V4.

Steve

Shroud_Pmodeler_PatchCommand_RV5.3dm (426.8 KB)