Houdini - Procedural Modeling Tips! - Finding Bridges

hi guys andy pixel here and in this video we are going to take a look specifically at how we produce bridges all right so we've kind of covered roads a little bit uh most notably the uh guard rails with the curvature video this time what we're going to do is we're going to look at how to produce the proper curves to produce bridges here all procedurally so if i were to go and move this curve around you can see that my entire environment here is actually updating so all the card rails are updating but the bridge is also updating as i move the curve around to accommodate the terrain at that level so what we're going to do is learn how to produce the proper data to produce a bridge from curves all right so let's get started okay so let's get started by building our terrain and bridges here so we're going to start with the grain but i'm just going to put this all inside of one geo container here so i'm going to drop down a height field and i'm going to change the size here to 200 by 200 just make it small we don't need a large train for this and then i'm going to go and drop down a height field noise node like so and i'm going to pick a noise that i like so i went with something around 600 for the amplitude and about 129 for the element size and i can play around with the roughness a little bit really depends on what you're looking for that's going to be good and then let's go and create a height field clip node and for this one i want to kind of set where the bottom of the terrain is and so i'm just going to use a min clip for this so this allows me to actually clip the terrain off so this is basically going to be where all the water is for this particular landscape and then i want to do another clip and we need to make sure that we get the height field clip node there we go and i want to clip off the tops here so you can also hit the compute range and then just kind of move your way down from there i really just want to create these kind of plateaus like so and then what i like to do is go back to the noise here and actually pick a location for this guy i used negative 77 and negative 89 for the location of the noise which gives me a nice place to put a bridge it's really what i was looking for there and we could bring this down even more i really want kind of a flat top something like that it looks pretty good uh you can also play around with these clip strengths here and the soft clip strength maybe get a deeper channel going there looks pretty good all right and then i'm going to do a mask clear i don't need that mask anymore and then i want to go and do a height field distort so let's get a distort node distort by noise there we go and i just want to go and just kind of rough it up a little bit make it look more interesting more terrain like looks pretty good all right and then i'm going to do a visualize and i'm not going to get all fancy with the visualization in this particular video here just want to get something so i'm just going to do a compute range and i'm going to get rid of all these color knots here just by clicking and dragging them and i'm going to make this more of like a darker mud type color and then we're just going to come over here and do kind of a nice terrine green and i'm going to go and clamp these guys here so get a harsher transition looks pretty good all right so i'm going to select all these guys hold down a on the keyboard and then left click and drag upwards to organize those guys i'm going to drop down a new grid and this grid now needs to match the size of this particular guy so i'm just going to copy this parameter go down to the grid here paste that into the size option here so now we have a grid that's the same size and this is going to act as my water plane so i'm just going to drop down a color node and we're going to go and give it a nice water type color and then let's just merge the two guys together here by selecting both hold down alt left click and drag off of the knot there for the output see that one more time there we go and now i've got a pretty nice setup there for a terrain that we can use and the color here doesn't seem to be coming through all that great it's picking up a little bit of the terrain colors there uh let's just go and drop down a attribute create node and what i'm gonna do is uh call this alpha i'm gonna give the water a little bit of uh transparency i'm gonna put it at uh 0.5 there we go that will work for our terrain so i'm gonna go and drop down a null node we'll call this out terrain all right so with that done let's put a net box around this stuff here so i'm just gonna select all the nodes do a shift o and we're gonna call this step one call this create terrain and give a color by hitting c on the keyboard and selecting the black swatch there or whatever color you want now we are ready to go and create our bridges one thing we can do is make this a little higher res so let's go up to our height field node up here and in the grid spacing let's do something like 0.75 there we go so now we've got much higher res terrain there all right so let's take a look at calculating the bridges from a single user curve so let's drop down a curve node here and this guy is going to be our user curve so if you're building an hda this will be exposed to the actual hda so it can be edited in like the houdini engine or outside of this particular geo node and then i'm going to go down and hold down my alt control and left click and that will template this and then i can draw on top of my terrain so if i hit spacebar 2 and hit enter on the keyboard in the scene view here and we'll just draw some sort of like road like thing yeah something like that looks pretty cool all right i want my curve here to actually sit on top of the terrain so i can cast right down and snap this to the train and so to do that i like to go and drop down a transform node just in case the user curve comes in with values that are in y and i just put the scale to zero in y and that flattens it out and then we can use a match size node so let's drop down a much size node and let's feed in an object for the second input here so i'm going to drop down an object merge node and this is going to be called get turing and i'm just gonna feed in my terrain here so let's just drop this guy down here like so and um yeah let's uh pipe this guy into here very cool you can see the batch size node will actually take into account the second input's geometry bounding box size so we can then use the justify and set this to max so that the curve is sitting right on top of the terrain there all right so at this point i'm going to resample the curve and i'm going to start out with a high value so i'm going to do something like a 4 for this and then i want to make sure i turn on my subdivision curves you can see here if i turn on my point display we have a good resampling for this particular road here i'm going to start with larger values just because we're going to work our way down to smaller values as we get more detail going here all right so then we want to go and snap this to the terrain so i'm going to call this guy snap to terrain and for the second input here i'm going to feed it the terrain there and for this i'm going to utilize the volume sampling trick that i showed you guys in a video a little bit ago and so this is the code right here so you can copy that i just saved it as a preset so that way i don't have to type it over and over and over again all right so now we're snapped to the terrain perfectly you can see that it missed the water because this particular technique here is only looking for volumes and our height fields are volumes what we need to do now is we need to go and figure out how we get the curve to be above the terrain here right and so to do that we're going to be doing some blurring and so i need to go and drop down a group by range node here and just group the ends you can also do it with backs as well but i'm going to do it with a group by range node this time let's uh go to points and we'll set our start end to one and one and we'll invert it and that will go and group just the end points there which is perfect for us all right so at this point i need to go and drop down a polyframe node and this time i'm going to type in n a capital n for the tangent you can also save a preset for that so you can see i have a couple here all right and that will create for us our flow normal and then finally we want to go and get our slope here so i'm going to call this get slope because what i want to do is i want to find the areas that have really high slopes in here and what that will allow us to do is it'll allow us then to blur those areas which will actually lift this portion of the curve up these areas over here don't have a high slope and so they won't generate any sort of bridges or anything like that so let's do this in order to do this if you haven't seen the path slow production video i highly recommend watching it i'm going to call this a new vector flat norm it's going to be equal to the current normal which is our flow normal and then for that flat norm i'm going to set its y component to zero and then we're going to normalize it just so we have a unit length of one so we're going to say normalize and we're going to say flat norm and then to get the actual slope in degrees i'm going to create a new attribute called slope by typing an f at attribute stands for a float type of attribute and we're going to say degrees and we're going to get the arc cosine of the dot product of the current normal and our flat norm that will give us our slope in degrees there and i need to type in dot for this guy i missed one there we go beautiful all right so now we have our slope now one way you can actually visualize this is you can utilize the visualizers here you've probably seen that i've used the visualize node over here by just creating a node or you can also select node and hit x on the keyboard alright or you can come over here and you can right click on this little guy and you can say i want to create a new visualizer by hitting this plus button right here and i want to create a new marker and for this i want to go and look at that slope value so i set the class to points because it's on the point class and i just want to set it as a marker so now we have really quick access to our visualizer so you can see that we have all of our slope values here and you can see the area where there should be a bridge we have some pretty high slopes so it's a pretty good way to find all this stuff now if you want to turn off the visualizer just right click this and just turn off the little check mark so a little bit faster than using the visualize node all right so now we've got the slope going there um i want to go and find the maximum slope that we have so let's go and do an attribute promote so i'm just going to go and type this in here we're going to do max slope and we want to go from point because currently our slope attribute is on the point class let's go from point to detail we want to take the slope and we want to get the maximum value let's change that new name let's call this max slope and let's make sure not to delete the original there all right so with that done let's go and drop down an attribute remap node and this remap node is going to remap our slope into a value of zero and one all right so let's go and select the remap node there and our original is going to be slope our destination our new name is going to be slope as well so we're just going to overwrite it and then what i want to do is i want to get the maximum value from this attribute promote so to do that we're going to type in detail 0 for the first input and the remap node only has one input so that'll work and we want to get the max slope and we want to get the first index of that because it's just a single flow value so now we've got that maximum value and if i were to go and look at the slope now so let's turn on our marker that we made you can see that we have a value that goes from 0 to 1 depending on our max slope values all right so we can use that now let's go and blur this and let's actually let me show you really quickly let's untemplate our terrain here let's go back to our marker by right clicking on it and then we can go and edit the marker now by hitting the little pencil icon right here let's actually change it to a color and let's close this guy out and turn off our point displays so now you can see where our slope is the most intense which is right around where the bridge should be which is great so we're going to then blur that value so i'm going to say blur slope and we are then going to type in slope for the attribute to blur we're going to turn off pin border points and you can see now as i move this guy that the visualizer will update so you can see it's kind of hard to see but there you go so i'm going to set this up to something like oh i don't know 200. actually let's do 50. 200 is probably going to be a bit much so i'm going to set the step size to 1. so that just gives us a really nice gradient all right very cool what we can do with that value is we can drop down another attribute blur node and we can then blur the position so i'm going to use that slope value as a weight attribute so let's type that into the weight attribute so what's going to happen in the blur node is it's going to use that 0 to 1 value our slope value and it's going to blur it more intensely where our slope is more intense all right so let's go and do that so i'm going to set this one up to about 200 and we are going to turn off our pin border points and we also want to make sure you can see that when i move this slider it's actually moving our endpoint so i want to say not ends up here or exclamation mark ends and that will pin our endpoints to where they were originally located so now i'm just going to set this to something like 200. all right so if you can see now if i were to template my original curve you can see that the greatest changes in the curve appear right around where the bridge should be and these other guys would be tunnels basically based off of some sort of height threshold all right so cool now we've got our curve that we want to use so i'm going to drop down our wrangle node and this one is going to be to set the y pause i really am just interested in the y position of this curve and i want the x and z positions of this curve all right so that's what we're going to do here so to do that we're just going to create a new vector called other pause and we're going to make that equal to a point expression or point function that is looking at the second input it's going to get its p attribute and we're going to look it up by its point number and because both these curves are the exact same point numbers that'll work all right so at this point let's resample this now let's go down to a lower sampling rate this time i'm going to do something like 1 this will just give us more detail to work with and let's also make sure we turn on our subdivision curves uh the other thing i forgot to do let's actually set the p dot y up here to our other pause dot y there we go so now you can see we retain the x and z position but use the y position from this curve that was that has been blurred out so now we need to go and find out the height from the terrain that a certain part of the curve is at all right so to do that i'm going to go and grab my terrain i'm going to drop down a another object merge node you could always come up here and just copy this guy and drag it down here so do an alt left click drag so now i have my terrain over here let's uh template it by holding down control and left clicking the template flag we'll take a look at our curve here all right so i need to go and sample the terrain and figure out the heights from each point to our particular curve there all right so to do this i always turn to my trusty effects all right so we're going to say find height and for this just like what we did up here for the snapping to the terrain we're going to do a volume sample because you can see that we're returning the height so we basically want to just copy this same set of code here for the vex and we want to paste it into there but this time i don't want to actually set the height to the curve i want to keep this particular portion of the curve this time what i want to do is i want to say f at disk to create a new distance attribute that lives on each point and i want to then go and subtract the current points position from our height that we just sampled and i need to make sure this is a period there we're going to negate that and then finally i'm going to colorize this just so we can visualize this particular distance value so i'm going to say at dist so if at this is less than negative 1 let's just start there so 3 feet then we want to basically give it a color of red so let's do one zero zero for red else we want to just color it green that'll just be a road area so i'm just going to go and pump that in there we go and voila we now know if i were to template my terrain again turn off my point display you can see everywhere where a bridge will be considered right so you might have a little tiny bridge there you might have a little tiny bridge there you can always get rid of those guys and only take the really long ones all right so now we know where all that stuff is all right so we know a bridge is going to go right here and this has a potential for being a bridge at this point then what we need to do now is break off these sections of the curves from the green area so we want to get just the curve that are all red and just the curves that are all green all the green curves will be the roads and all the red curves will be the bridges so to do that i'm going to use a convert line and we're going to convert all of these into individual segments or primitives here perfect so i don't need to keep the wrestling so i just turn that off and i'm going to then go and promote my color value so i'm going to do attribute promote we're going to promote this from points to our primitive because we now have individual primitives per segment you can see it creates a nice clean value but it it is actually producing like a yellow value so i do want to go and get just the first match so now we have a very clear cut between those two guys so at this point i'm just going to drop down a split node and we're going to use a little expression we're going to say at cd dot r is greater than zero and that'll leave us with just the bridge curves just for good measure let's set this to primitives and now what we can do is drop down a null node and we can say out bridge curves and then left click and drag with alt held down and say out road curves like so i'm just going to drag these guys down because we're not done yet remember all these particular curves here are still broken up in individual segments so i don't want that and so all we need to do is just drop down a fuse node and a polypath node and that will turn them back into single primitives per curve there and then finally we're going to need a value for these so we can loop through each one of these guys and currently we have this prim number that identifies each bridge segment by itself but i need to actually create a id value for this so primitive all i'm going to do is just go and write a little tiny backs here i'm going to say i at id is equal to at premnum this will help us when we drop down a couple for each loop nodes and start working on the individual segments so different bridges here because you could end up having different types of bridges for the overall distance that it's actually traveling like this one would be a really big bridge and this one would be a really small bridge because remember it's based off of its distance value all right and let's just do the same thing for the roads and there we go so now we've got our bridge curves and we've got our road curves last step here is just uh select all the nodes do a shift o and we will then go and call this step two find bridge curves and then give it a little color i tend to go for the black very nice all right so now we've got all that data you're pretty much good to go all we need to do is drop down a couple sweep nodes and then build our bridges and we'll have some roads and bridges and so after a couple of hours uh this is what i came up with so i literally just started with these bits of data and the terrain so i did just a couple of things you know for the terrain for the water um in order to get this nice cut out i just used a boolean so i just took the original drain and an extruded version of the water and then just bullied it out and then just remeshed it to get a nice mesh out of that and then moving on um this was the final terrain right here so nothing awesome to look at there it's just really basic and then for the road so in this case i took both curves the road curve and the bridge curve i also made sure to put an attribute blur onto the actual bridge so that way it's nice and flat um i also went up here and removed all the small bridges so to do that you would just drop down a measure node and find the perimeter and then go and delete all the small bridges and then you could do something else with them after that maybe they're just like a retaining wall type of structure so yeah then i ended up with the roads and then we got my final bridges which i didn't really spend a ton of time on this it's just really basic uh version of the bridge added some foliage just like so all just using a scatter node nothing nothing really complex or anything like that um i can walk through the nodes here so i brought in the train just added some point normals created a really basic mask used a mask from geometry node to mask out where the path was and then scattered it on using that mask value as my density for the scatter points and then just copied some stuff to it some really basic little poly models and then i created the foam so for the foam i use the ab seam so if you come over to the boolean node over here um i output the a b seams and then that allows me then to go and um extract those particular curves with the edge group to curve node so you get those guys and then i just peeked it out and then uh created two more lines there and then just did a sweep with a random p scale on it and gave me something nice and stylized there which i was going for then finally the guard rails which we saw a couple videos ago in the procedure modeling tips video series and then that is that i ended up with this guy it turned out pretty cool i like it and then i also went and set up a basic uh karma render here for this nothing crazy either all the materials are all just principle shaders there we go so this file is available to all the patrons on the any pixel patreon page if you're interested definitely go check it out and uh so yeah that is how we do bridges there's at least one way to do bridges um you know what they're doing there's a hundred different ways thousands of different ways to do things so hopefully you guys like that technique and thanks much