Posts Tagged ‘TIN’
Creating vertical profile graphs
Problem: You have some contour lines and want to chart elevation changes along a path
We got a 3D view of a neighborhood in my previous entry about displaying data in ArcScene. As I was panning around I got to thinking about what it would be like to sled down some of those hills. This one cul-de-sac looked particularly nice.
Hikers sometimes use topo maps to make vertical profile graphs along prospective trails so they know what they are getting into. Engineers use them when they are working on the grade of the new road. Today, we’re sledding enthusiasts wanting to see how much fun we’re going to have come winter.
In order to create a profile graph down the hill I spotted, I will need to move all my layers back into ArcMap. I’ll need the TIN surface to provide the height information and the roads so I know where to draw my line.
Once you’ve brought the layers up, go to Tools –> Extensions… and make sure you have the 3D Analyst extension checked on. Then go to View –> Toolbars to turn on the 3D Analyst toolbar. 3D Analyst needs a raster elevation surface to work with. If you are starting with vector topo lines, you’ll need to create a TIN (Triangulated Irregular Network).
As I explained in my ArcScene entry:
To do that, go to the 3D Analyst drop down menu, and select Create/Modify TIN –> Create TIN from Features. You just need to tell it which feature layer to use to create the TIN, which attribute has the height information, and which triangulation method to use. Soft Line is best for topos.
Make your TIN the target layer. Your screen will look something like this.
Now, press the Interpolate Line button that I moused-over above. Then, draw a line along the middle of the road from the point where the imaginary sled will start to the point it will stop. The line will show up as a graphic element. Make sure it is selected (it should be by default) and then click the Create Profile Graph button. Here’s what mine looks like:
Hmm, not really the even downward plunge I was hoping for. Good thing I checked! If you right click on the graph and select Properties… you can change the titles to make them more descriptive.
I edited my main title and bottom + left axis labels to get this.
Note: You can change the appearance of the profile line on the Series tab, and you can change the appearance of the entire chart under Advanced Properties.
I have found it a good idea to create a vector line over the top of the graphic element profile line. That way I’ll have it saved in a format that I can bring into other maps or, for instance, bring back into my ArcScene view.
Tags: 3D, chart, TIN, topography, vertical profile
Displaying in 3D with ArcScene
Problem: You have some elevation or multipatch data that you would like to visualize in three dimensions.
For several of my entries I have been using layers from the robust catalog over at DC GIS. They offer pretty much everything needed to make a map of the District. In addition, some of the data layers contain elevation information, such as the 1 meter topo lines and the mulipatch buildings.
Note: Multipatch is a unique geometry type that can contain 3D models with vertical and overhanging faces.
These layers lend themselves to being rendered in 3D, and ArcScene has been formulated for that purpose.
ArcScene will show up in your Start Menu along with ArcMap and ArcCatalog. There is also a button that launches it from the 3D Analyst toolbar.
You can add data to ArcScene using the Add Data button just like you would to ArcMap, but it will look very different. Any of the height information embedded in the layers will automatically be applied to form a 3D world.
Here’s how the multipatch buildings, topo lines, road areas, lot boundaries, tree points and swimming pools from DC GIS look when I first add them.
It’s pretty neat, but needs some work. Some of layers, like the lots and roads, appear to be floating beneath the ground. This is because those layers don’t have height information, so ArcScene doesn’t know where to put them. In order to proceed, we need to make a surface from those topo lines. To do that, go to the 3D Analyst drop down menu, and select Create/Modify TIN –> Create TIN from Features. This will create a Triangulated Irregular Network to act as an opaque ground surface that the other layers can be draped over.
You just need to tell it which feature layer to use to create the TIN, which attribute has the height information, and which triangulation method to use. Soft Line is best for topos.
Now I have a solid ground surface with realistic shadows to enhance the 3D effect.
In order to raise up the other layers so they sit on top of the ground, right click on them to open their Properties. Then go to the Base Heights tab and tell ArcScene to obtain their heights from the surface you just created.
I did this for all my layers and also changed the symbols to some more pleasing colors. Now it’s looking like a real neighborhood!
Those multipatch buildings are by far the coolest part. They’re likely pretty rare in the typical GIS catalog, however. If you’re like most people and just have normal (boring) building footprint polygons, at this point your scene would look thusly:
You can add more realism by “extruding” the buildings up from the ground by a uniform height. Go back to the Layer Properties and click on the Extrusion tab.
Play around with different values until it looks right. I found that 8 was about the height of most of the multipatches. It just looks like they’ve all got flat roofs now.
If I wanted to, I could extrude the roads and swimming pools just a bit too. I tried it, and decided they looked better flat. I also changed the tree symbol to Big Leaf Maple (available through More Symbols –> 3D Trees), checked off the Edge Types symbol on the TIN, and turned on the lot boundaries as hollow polys. Just some ideas to show you different things you can do.
Whatever you do, you are going to want to try a fly-through. You won’t be able to resist. I sure couldn’t.
Press the button that looks like a little bird, then click in the scene where you want the bird to go, and use the mouse to soar through the streets at eye level. If you are giving a presentation, this is a guaranteed crowd pleaser. Here’s some “photos” I took while flying through my scene.
Tags: 3D, ArcScene, multipatch, TIN, topography