Subsurface plume volume and 3D model.

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09-27-2011 11:55 AM
JaysenGaines
New Contributor II
Hi. I have a project where a client wants a 3D model of a soil contamination plume, and they want a volume measurement of the amount of contaminated soil. No one at my company has used 3D analyst before, and I have been a GIS analyst for all of 3 months so I am hoping someone out there can point me in the right direction.

We have an ArcView license with a 3D extension. The field technicians are taking a GPS reading at each sample location as well as elevation (above a known benchmark), contamination concentration readings at several depths (2', 4', 9'), and a final depth at which the contamination is no longer detectable.

I can create maps of the various contamination levels in ArcMap, but the 3D model of the plume is trickier.

My idea is to use the spatial analyst kriging tool in ArcMap to create a raster from the final depths. Then I turn that raster into a TIN in ArcScene. Then have the depth_TIN float below a TIN I created from the elevation data. At this point I assume I can use a volume tool to obtain the volume inside (or above the Depth_TIN and below the elevation_TIN) of the "plume" I created.

If anyone knows of a more accurate or efficient method, or sees a missing step please let me know.

Any and all help greatly appreciated,
Thanks
J
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5 Replies
JakubSisak
Occasional Contributor III
Is determining the volume of the contaminated soil the ultimate goal or do you need to visualize this? You need to build something like an isosurface or a 3D voxel grid from your input data then determine its volume which is something 3D analyst cannot do. 
If you just need a rough model then you can create sort of a layer cake multipatch model in 3D by extruding between surfaces to obtain a multipatch geometry for each level.  In geology software for example a lot of interpretation goes into creating subsurface models so using a similar approach you could separate your data into groups of points by elevation then using the sample points as a visual guide draw approximate polygons defining the outer most extent of the contamination for each elevation group (every x metres).  Each time you complete a polygon for one level you asign it a height field. What you end up with will be a series of flat polygons stacked on top of each other when you view the results in ArcScene.  You can load in your points at the same time and QAQC your results.  The stacked polygons should already resemble the shape of the plume.  Next step is to use the extrude between tool to create a 3D multipatch for each level. when you do this for all the levels and add it to ArcScene you should basically have a rough 3D model of the plume.   You can use the Union 3D tool to merge the layer cake together into a single model. Your multipatch should be closed so you can use the add Z information tool to obtain volume. This is essentially a similar process to how subsurface solid object are created in geological software except there you can digitize in real 3D space (snapping to drillhole assays,  points in space or whatever else is loaded) and create your polygon slices inclined and in whichever direction. You can then connect the slices with directional polylines in 3D space to "tell" the software in which direction to build the mesh.
In truth, 3D analyst is not the tool for subsurface modelling. There is no actual way to digitize multipatches from scratch in 3D space. You can import multipatches from 3D DXF created in datamine studio, Gemcom, Leapfrog, Geosoft, etc. but then what? You can't label anyting in 3D, you can't produce a decent vertical section, you can't import drillhole data or borehole logs which is how most subsurface data is obtained. I didn't even find an easy way to set a specific plunge and azimuth in arcscene.

There are other ways you could build the multipatch such as using Google Sketchup - Collada. The problem is that in version 10 you can only export collada to Sketchup from ArcGIS. First you have to create a multipatch then convert to Collada then export to Sketchup. This is only an OK process for buildings and such - you export boxes and make them look like buildings in Sketchup then bring them back to ArcScene. Up to version 9.3.1 you were able to use the Google Sketchup plugin for ArcGIS which allowed you to export points, polygons, polylines and TINs as well so you could have technically exported your point cloud then make a 3D object of the plume in sketchup and then bring it back. Georeferencing was an issue though so you needed to export control points with then georeference the model back to these control points. Still i used to do it a lot. Gone are the days were i was able to easily export a complex surface model from TIN to sketchup without any issues. The Collada way is too buggy. It only handles simple polygons and you are lucky if something does not die during the process. So it really only works for buildings.

You might find a lot better answers on GIS StackExchange forum. Most of the GIS wizzards that used to frequent the ESRI forums have moved there and there are some serious experts there. In my experience questions that have to do with interpolation or 3D modelling receive a lot of attention.
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JaysenGaines
New Contributor II
Thanks Jakub,

I need to both visually represent the data and provide a volume of the contaminated soil.

I thought of the "layer cake" method at first when I was told there would be samples derived from many different depths for each boring. But as the project progressed I learned that these results (from each depth) can be represented with a 2D map, and once the final depth at which contamination can be detected is determined for each boring I will then use that measurement to create the the 3D model.
From your response it seems I may have to have a meeting with the project manager and tell him that this is not as cut and dried as I had hoped. I am still optimistic that I can create a 3D surface using final depth as the Z field and determine the volume of plume that way, but I may need much more data than the client has provided for me.
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JakubSisak
Occasional Contributor III
The reason I am suggesting to create the plume using the layer cake interval method is because I personally don't know of any way of creating a closed multipatch with a volume using a point cloud.  What you need to do is very easy in very expensive software. In Leapfrog you can use 3D interpolation such as bihormonic spline for example to quickly generate a closed 3D mesh surface with volume. 3D Analyst provides a way to import such model but not to create it.
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JaysenGaines
New Contributor II
Leapfrog3D looks amazing. I'm sure it would do the trick. However getting anyone around here to purchase new software is a nightmare. You said it was expensive? They do not list a price on their website so I'll get in contact with a sales representative and see what we can work out. Since this is our only current project where 3D modeling is required I fear I may not be able to justify the purchase. I may have to find a work around.

Thanks for your help and suggestions so far.
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JakubSisak
Occasional Contributor III
Leapfrog is amazing. Truly. I had no idea until I started using it. Personally, I use Leapfrog Mining but Leapfrog Hydro might be more suitable for your application.  I've heard great things about it. I've used a number of 3D applications and do some developing myself but I have to say that I have never used anything like this software. It is polished.

My company purchased the licenses and I believe it's about $10,000 per year. You cannot actually outright purchase this software.

Training is really hard to come by (at least here in Canada) so it consist mainly of 2 - 3 day customized workshops where you have to book the instructor and fly him to your location.  However, after you install a licensed version of Leapfrog you can print the help manual which consist of detailed step by step tutorial and an in-depth reference manual.

If you are in the States you could attend the November 2011 NWMA in Reno. Aranz Leapfrog is running a course there.

Here is some info and visuals
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