I have a low-quality mesh, I want to remesh it but keeping the topology(only adjust the vertex position, keep vertex size, face unchanged). Is there an exist method could do this in CGAL?
There is a remesher in CGAL. However, it will recreate a surface with its own vertices and faces number, depending on the criteria you ask for. You can give it a try by compiling the Surface_mesher demo or using the precompiled windows demo (you need this and this).
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I'm a big fan of PaperJS, however, the library doesn't see much activity so we're looking at other tools, like KonvaJS, Fabric, and Pixi. We'd like to replicate the example here:
http://paperjs.org/examples/path-simplification/
in KonvaJS but we're not sure which class is the most appropriate? Should we use the line, which is described as a collection of points with tension, the path tool which is what we use in Paper, or the shape class? Does KonvaJS offer the same type of access to the bezier curve tools and shape border, blue line, found in the above-mentioned paper example?
Konva.Line requires a list of x & y passed into its points property as a simple array, then draws straight lines connecting those points. The tension property can be used to make the straight line joins more curvy.
Konva.Path expects you to provide a data property that is more like a list of SVG drawing instructions, so move, lineto, arc, etc. (See supported instructions list in Konva docs for Konva.Path.data here)
There is no built-in equivalent path-editing features to those in the demo you linked to - so no automatic anchors on the path control points and no Bezier handles. You would have to DIY those. Having said that, it would all be achievable - what I mean is the drawing of the control anchors and lines, the listening for mouse and drag events, and the final passing back of the SVG drawing data to the Konva.Path shape when the path's edit mode ends are all well supported in Konva.
As at May 2022, the Konva lib is well supported, with appropriately frequent (as Goldilocks would want - not too many and not too few), no ill-thought-out breaking changes, issues are responded to, SO posts replied to, and there is a busy Discord channel.
I'm having trouble finding a way to solve this specific problem using MeshLab.
As you can see in the figure, the mesh with which I'm working presents some cracks in certain areas, and I would like to try to close them. The "close holes" option does not seem to work because, being technically cracks and not holes, it seems not to be able to weld them.
I managed to get a good result using the "Screened Poisson Surface Reconstruction" option, but using this operation (rebuilding the whole mesh topology), I would lose all the information about the mesh's UVs (and I can not afford to lose them).
I would need some advice to find the best method to weld these cracks, which does not change the vertices that are not along them, adding only the geometry needed to close the mesh (or, ideally, to make a weld using the existing edges along the edge).
Thanks in advance!
As answered by A.Comer in a comment to the main question, I was able to get the desired result simply by playing a bit with the parameters of the "close holes" tool.
Just for the sake of completeness, here is a copy of the comment:
The close holes option should be able to handle this. Did you try changing the max size for that filter to a much larger number? Do filters >> selection >> select border and put the number of selected faces as the max size into that filter – A.Comer
Is there an easy way to show 3D entity at all times, even when that entity is hidden behind another entity? For example, I want that lines are always shown event when they are behind mesh surface.
I use Qt3D framework.
Assuming that you are talking about the Qt3D framework I want to extend the answer of Rabbid76.
To disable depth-testing in the Qt3D framework, add a QRenderStateSet to the framegraph branch that renders things (the one that as a QViewPort for example) and add a QDepthTest to it. Then, set the depth function of the QDepthTest to always. This way, the depth test is always passed and entities in the back will also be drawn, depending on the drawing order. You can use QSortPolicy to adjust the drawing order to back-to-front.
But this won't work when the camera position changes and your entity that you always want to be drawn is in the front. I'd suggest you add another framegraph branch and use a QLayerFilter to only deactivate depth-testing for this one entity.
If your entity looks weird when deactivating depth-testing (likely for complex objects), you could replace the QDepthTest by a QClearBuffers and simply clear the depth buffer.
Have a look at my answer here, where I showed an example of a custom framegraph with depth test.
If the depth test is disabled, then the geometry (like a line) is always drawn on top of the previously drawn geometry. The depth test can be disabled by:
glDisable(GL_DEPTH_TEST)
See glEnable
As an alternative the depth test function, can be set to let a fragment always pass depth test. In Qt this can be done by the class QDepthTest, using the enumerator constant Qt3DRender::QDepthTest::Always.
In this case, you have to take care about the order in which the geometry is drawn.
You have to find a way, to render the polygons (opaque geometry) first, by using the depth test function Qt3DRender::QDepthTest::Less.
After that you have to render the lines on top, by using the depth test function Qt3DRender::QDepthTest::Always.
Firstly,I use google static map API to get the image to display on html/wml.
And then, I want to get the point's GPS position where user pressed on the image.
Is there some way to get the GPS position if I got the co-ordinates on the image?
The short answer is probably not. You can't be sure exactly what the static map's dimensions are (the server might change the location slightly to fit things better, etc.). If you're just asking for a map by center and zoom then you stand a slightly better chance, but it will still be tricky.
If you're trying to add dynamic behaviour to a static map, have you considered instead the Maps JavaScript API? Finding the coordinates of where a user clicks is trivial there. (Also, you can disable the zooming, panning, controls, etc. if you want so that it still feels like it's static).
I have a map that I converted from a raster graphic into an SVG file by converting the differently coloured areas into paths.
I know how to do a basic point-in-polygon check given an array of edges, but the svg:path elements represent multiple polygons as well as masks (to account for seas etc) and extracting that information by parsing the d attribute seems rather heavy-handed.
Is there a JS library that allows me to simplify that check? I basically want to create random points and then check whether they are on land (i.e. inside the polygons) or water (i.e. outside).
As SVG elements seem to allow for mouse event handling, I would think that this shouldn't be much of a problem (i.e. if you can tell whether the mouse pointer is on top of an element, you are already solving the point-in-polygon problem).
EDIT: Complicating the matter a bit, I should mention that the svg:path elements seem to be based on curves rather than lines, so just parsing the d attribute to create an array of edges doesn't seem to be an option.
As the elements can take a fill attribute, a ghetto approach of rendering the SVG on a canvas and then finding the colour value of the pixel at the given point could work, but that seems like a really, really awful way to do it.
The answers on Hit-testing SVG shapes? may help you in this quest. There are issues with missing browser support, but you could perhaps use svgroot.checkIntersection to hit test a small (perhaps even 0 width/height would work?) rectangle within your polygon shape.
The approach I suggested as a last resort seems to be the easiest solution for this problem.
I found a nice JS library that makes it easy to render SVG on a canvas. With the SVG rendered, all it takes is a call to the 2D context's getImageData method for a 1x1 region at the point you want to check. I guess it helps to create a copy of the SVG with colour coding to make the check easier if your SVG is more complex than the one I'm using (you'll have to check the RGBA value byte-by-byte).
This feels terribly hackish as you're actually inspecting the pixels of a raster image, but the performance seems to be decent enough and the colour checks can be written in a way that allows for impurities (e.g. near the edges).
I guess if you want relative coordinates you could try creating a 1-to-1 sized canvas and then divide the pixel coordinates by the canvas dimensions.
If somebody comes up with a better answer, I'll accept it instead. Until then, this one serves as a placeholder in case someone comes here with the same problem looking for an easy solution.