A while ago I wrote about a project I am working on to estimate the amount of fill dirt we need to order to re-landscape the driving range of a golf course.

I used our existing 2-foot topo line files to create a GIS surface of what it looks like now.

how it currently looks


The next step was to create a surface of how we want it to look after the fill dirt is dumped and graded. To calculate the volume of earth we need all I have to do is subtract the current layer from the new layer.

I finally got around to working on this again yesterday. I thought I would just draw a bunch of topo lines by hand and attach an elevation to each line. Easier said than done. Our minds don't work like that, or at least mine doesn't.

After sitting and staring at my screen for a while I decided on a new approach. One of the things the software can do is take a bunch of GPS points that have been collected and create a 3D surface from those. I will just make my own "GPS" points and add the elevation for each one. My desired end result is a surface, not topo lines, so this will be fine.

Here is what I constructed:


click for full sized image

I started with the highest existing point which will not change. It is the cluster of pure red dots just a little bit up from the bottom. This is the tee. From there they want a 1% downward grade to the north. I plunked points from the tee going north and then calculated the elevation for each point given the distance it was from the tee. For every 100 feet from the tee the elevation will decrease by 1 foot.

The next thing I did was create points around the perimeter of the project and gave them the same elevation as the topo lines they intersected. This is how the new surface will have a nice seamless transition with the existing surface.

At regular intervals around the perimeter I would make a series of points going inward. They want the perimeter of the range to have 33%, or 3:1, grade. For every 33 feet from the perimeter the elevation will increase by 1 foot. I just did the same kind of calculations for each point, but once the elevation reached the elevation of the initial series of points from the 1% grade I just set the elevation the same as the portion of the 1% grade it was intersecting with.

In the dot picture the red dots are the highest, the green dots are the lowest, and the yellows and ambers are in between.

If everything goes alright tomorrow I will model these dots into a 3D surface and calculate how many yards of dirt we need. I will of course post an image of the surface.