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Subject: UV mapping an arch? Help!


maclean ( ) posted Wed, 26 November 2003 at 6:34 PM · edited Thu, 28 November 2024 at 2:22 PM

file_85750.jpg

Well, I have to admit, I'm stumped. I thought I could handle pretty much anything in uv mapper, but this one's got me. The pics - This is the last body part of a figure I'm mapping. An arch above a doorway. The part that's giving me trouble is the arched top piece of the wood. The rest's OK. On the template, nothing's positioned or scaled yet. Just thrown around until I get the arch done. I mapped the horizontal bottom bar with cyl cap/X-axis. Then I mapped the center vertical bar with cyl cap/Y-axis, exported the uvs, then re-imported them for each of the other 4 vertical bars, which gives me top to bottom grain on each one. So far, so good. Later on, I'll scale them up to fill the template. But I'm damned if I can figure out how to map the arch itself. As you can see, it's a compressed and sliced tube and I can't think of a single thing to do with it. Someone surprise me with a wonderful idea, please! mac


maclean ( ) posted Wed, 26 November 2003 at 6:37 PM

PS I always map grain to run along the length of the wood, like it does in real life. How would an arch be made? I figured it would be a long piece of wood, bent into a curve. So the grain should run along the length of it, right? mac


MeInOhio ( ) posted Wed, 26 November 2003 at 8:42 PM

Guess I don't have any ideas on your problem, but something caught my eye in your post? You mapped one of the vertical bars and then exports and imported for each of the angled uprights. Does that mean if I have three windows and the one in the middle faces front and the other two are at 45 degree angles to the middle one, that I can map the front window and export it and then import it for the other two windows and that the map will apply correctly for the angled windows? And about you dilemma...could you map the top of the arch from the top and keep the sides of the arch the way you have them. Then you could apply a texture that runs around in a circle (like a disc the same size as your arch) to the side of the arch. Wouldn't that put the grain the way you need it?


Ajax ( ) posted Wed, 26 November 2003 at 9:48 PM

Make a separate material or group for each of the four sides of the arch, just so you can work on them separately. Make a cylindrical map of the arch. The axis of the cylinder should be at the centre of the full circle of which your arch is an arc. You will now have your inner side coinciding on the map with your outer side and the two window face sides will be mapped as zero thickness lines either side of the polygons of the inner and outer surfaces. Next, select the inner surface material/group and translate it to one side. If all of your vertices are welded This will strech out the two window face sides as well as moving the inner surface off the outer surface. Then you can select the face sides one at a time and move them off to where you can work on them. The rest should be obvious from there. OTOH, if your corner vertices are not welded, the face sides won't be stretched out when you move the inner side and that's going to make life difficult. There are three ways to handle it that I know. You can weld them and then split them again later on. You can just planar map the sides and then slowly and tediously move the vertices to match where they are on the inner and outer sides or you can morph the whole thing in poser so that the inner side is wider than the outer side and the cylindrical map will give the face sides more than zero thickness, then morph it back after you've mapped. I've use all three methods on occasion. I'd recommend the first one as being the easiest in this case. As to how they're built in real life, there are two common methods. One involves steaming the boards and bending them into shape, which is hard and only works for thin boards. The more common method is to build the arc out of a number of smaller arcs, each of which is cut from a wide flat board. You often see that method on wooden cart wheels and on spinning wheels. You might be able to find some photos of spinning wheels where you can see the grain pattern and the shape of the joints.


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Lawndart ( ) posted Thu, 27 November 2003 at 12:33 AM

. Great info!


nerd ( ) posted Thu, 27 November 2003 at 3:18 AM
Forum Moderator

OR... Make a morph for your arch that pulls the curved piece straight. Map the straightened piece, then use the original OBJ as a MT to pull it back to it's original shape. Nerd


maclean ( ) posted Thu, 27 November 2003 at 3:28 PM

MeInOhio, 'Does that mean if I have three windows and the one in the middle faces front and the other two are at 45 degree angles to the middle one, that I can map the front window and export it and then import it for the other two windows and that the map will apply correctly for the angled windows?' That's exactly what it means. I've just finished a bay window where the left/right windows are set at a 45-degree angle. Plus each side had roller-blinds, crossbars, venetian-blinds, etc. I just mapped each of the pieces in the center, exported the uvs and re-imported them for the angled ones. It's one of iv mapper's best tricks. Otherwise, mapping angled abjects is a nightmare. Plus, any figure where you have to map multiple pieces, each one the same, just do the same trick. It's a big time-saver. Ajax, Your way sounds wonderful.... if I could understand it. LOL. What do you mean by 'The axis of the cylinder should be at the centre of the full circle of which your arch is an arc' Do you mean using the offset values? And which axis? The Z-axis, I'd assume. To complicate matters, my arch is squashed, so it's not even a true circle. Nerd, Your idea would have been great, and I tried it. I straightened the arch in Anim8or, did a cyl cap/X-axis and exported the uvs, then re-imported them, but the vertices were all skewed, and the result was horrible. I then tried lining up the vertices (an experience I wouldn't care to repeat often), but I can't get them right. I think I need to rebuild the arch at this point. I'm going to try a non-squashed tube, make a straightened version and get the uvs from it, then squash the arch by scaling it in poser. Then re-attach it to the rest of the arch, then stick it back in the figure. Or maybe I'll just forget the arch.... Thanks all mac


MeInOhio ( ) posted Thu, 27 November 2003 at 5:10 PM

Thanks for the tip, Maclean. That will be very useful.


Ajax ( ) posted Thu, 27 November 2003 at 5:17 PM

Sorry Mac. I sometimes forget that not every body speaks Euclidean geometry. For cylindrical mapping UV mapper allows you to position your mapping cylinder anywhere you like and orient it along any of the three coordinate axes (x, y and z). The cylinder has an axis of rotation. If you think of the cylinder as a wheel, it's axis sits where the axle of the wheel would be. If you think of your arch as part of a wheel rim, that wheel also has an axle position. You want the two axles (mapping cylinder axle and arch axle) to cooincide with each other when you map. However, you've just pointed out that doing that won't work perfectly because your arch isn't a true circular arc. Here's another, probably easier, way to do it. Box map the arch, then move the two curved portions to a place where you have some room to move. Scale them in the V direction until you can easily select all of the verices along the bottom edge without picking up any from the top edge, then use the assign UVs menu item to give all of them the same V coordinate. Do the same with the verices along the top edge. Once you've done that with each of the two curved portions you should have four rectangular maps corresponding to the four sides of the arch and you can just joint them up. This will produce some minor distortion towards the ends of the arch. If you want, you can correct this by selecting columns of vertices toward the ends of the arch and moving them toward the centre until each column of polygons is the same width. All of this would be a lot easier to explain with a few screenshots, but I don't have the right software handy at the moment :-(


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maclean ( ) posted Thu, 27 November 2003 at 6:01 PM

file_85751.jpg

Hi ajax, Thanks for the explanation. I'm with you now (more or less). The second method seems reasonable,but I'm not sure about a couple of things. Here's a screenshot of the arch (planar/Z-axis/unsplit, and scaled up/down - V direction, right?) to show you what I think the problem may be. See the way the vertices are skewed like that? It makes them difficult to deal with because each section is a skewed slice. Also, I'm not sure what you mean by 'select all of the verices along the bottom edge without picking up any from the top edge' It doesn't look possible to me with this geometry. I could always make a tube in uvm and delete the parts I don't want to slice it. mac


Ajax ( ) posted Thu, 27 November 2003 at 9:40 PM

Just use the laso selection tool to select the vertices along the bottom edge of the arch in that picture you've posed. You could also select them a few at a time using the rectangular selection tool if you want, but the lasso is easier. Once you have the whole bottom edge selected, assign a V coord to it to get the whole lot on one horrizontal line. Then do the same for the top edge so that at the end you wind up with an upside down trapezoid shap (ie, a four sided shape with the bottom edge shorter than the top edge) About the skewed polygons - this is what using a cylindrical mapping is meant to avoid, but even without the cylindrical mapping it isn't that big of a problem. If you use a box mapping, rather than a planar mapping, you'll get all four sides layed out. You may have to rotate some of them to get them all lined up right but basically you'll have two areas like the pic you've posted above, a rectange for the top side and a slightly shorter rectange for the bottom side. If you've used the scale option in your mapping dialogue (often overlooked but very useful feature - just remember to set your scale appropraitely under preferences), then after fixing the arched sides you'll find that the bottom side of the trapezoid is exactly the same length as the short rectangle and the top side is the same length as the long rectangle and all of the vertex positions match up. Once you've stiched the four sides together, you can x scale the vertices of the bottom side of the arch until the whole map is a neat rectangle if that's what you want. Rather than using the box mapping I've suggested, you might get better results by making four separate planar mappings - one of each side. Box mappings have six faces and sometimes you'll get some badly placed polygons on an object like this. The key thing is to have the four sides separate so you can work on them individually and to have them all the same scale, which you'll get by using the scale option.


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maclean ( ) posted Fri, 28 November 2003 at 2:25 PM

Thanks ajax, I'll give it a try tomorrow. I use 'Scale' for everything I map, then decide later how I'm going to size pieces. But what do you mean by 'set your scale appropraitely under preferences'. Do you mean the Aspect Ratio (I use 'fixed'), or am I missing something here? mac


Ajax ( ) posted Fri, 28 November 2003 at 3:23 PM

Each mapping tool has a little box saying "Scale Result" in the dialogue somewhere (I've been calling it scale option because earlier I was on a different machine and didn't have UVM to refer to for the exact name). In the general tab of the preferences dialogue there's a box called "Pixels Per Unit". If you double the number in pixels per unit, then scale result will make your maps twice as high and twice as wide. If you have the pixels per unit set to something too small or too big, you'll either get tiny little maps with scale result or ridiculously large ones. I find I have to adjust pixels per unit for every model. That's what I meant about setting it appropriately under preferences.


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maclean ( ) posted Fri, 28 November 2003 at 3:40 PM

Yes, I'm talking about the same scale option. The one in the dialog boxes. I always use that. But in prefs, mine is set to the default (50). I only use it to get a scaled map in the vertical horizontal sense, ie. one that's proportional. Of course, it's always tiny, but I just size it bigger using shift-+. I have to admit, I've never understood uvm's bizarre template sizes and the way it makes maps. A curtain figure I just mapped (more or less square in shape) has a template of 1024 x 83. Weird... I just ignore it's sizes and do it my own way. It always comes out pretty good. mac


maclean ( ) posted Fri, 28 November 2003 at 4:31 PM

file_85753.jpg

OK ajax, I'm back. This is the latest situation. I separated the 4 sides and used the front one to start with. That's it in the center. I selected all the bottom verts, assigned them all to one coordinate, then did the top. In the 3d view you can see the distortion in the tex. Any hope of getting rid of that? I tried unskewing by moving the bottom verts to one side, but it didn't seem to help much. mac


maclean ( ) posted Fri, 28 November 2003 at 5:33 PM

file_85754.jpg

LOL ajax, Me again. OK, I just rebuilt the arch. You can see the results here. A lot better now. I used a bent box for the arch and a straight version of it for the uvs. The large map (top right) is with the imported uvs. I haven't fixed the maps up yet. Just made sure it was all working. You can see the tex runs along the length of the arch and looks pretty good. I think I was making work for myself with the first version, but it was worth it. I learnt a few tricks from you. LOL Thanks for all the help mac


Ajax ( ) posted Fri, 28 November 2003 at 5:33 PM

Ideally you want the vertices along both edges to be evenly spaced all the way along. To save yourself work, you shouldn't do it until you've stitched all four sides together. Then it's a matter of selecting vertices and moving them with the arrow keys. Tedious but effective. You know, you could always just leave the sides as arcs and make the textures suit them that way. It would probably be less hassle as well as being lower in distortion.


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Ajax ( ) posted Fri, 28 November 2003 at 5:52 PM

Crossposted. Cool. That looks good. You're welcome. Glad you got something out of it :-)


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maclean ( ) posted Fri, 28 November 2003 at 6:09 PM

file_85755.jpg

Here's a last render. Mapped and in poser. cheers mac


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