From: Deepsea Dawn Date: July 31, 2007 4:08:18 PM PDT To: Deepsea Dawn Subject: Calculating_Volumes ASHLEY: From: "Ashley Booth" Date: July 31, 2007 10:33:49 AM PDT To: dawn@dusk.geo.orst.edu Subject: Calculating Volume I am a Research Technician in Dr. William Gilly's Lab at the Hopkins Marine Station. I have been using the Calcofi dataset to look at how oxygen levels have changed over time in the Gulf of California. The goal is to be able to quantify the volume of water within a certain oxygen range. We are investigating how the oxygen habitat of the Humboldt squid has grown or shrunk in the past couple of decades. I have been familiarizing myself with the 3D Interpolator tool and get the feeling that I might be able to calculate volume from one of its products. Do you have any suggestions on how to do this? Or know anyone that may be able to help? TIFFANY: From: Tiffany.C.Vance@noaa.gov Date: July 31, 2007 11:24:31 AM PDT To: Deepsea Dawn Cc: Ashley Booth , Joe Breman Subject: Re: Calculating Volume How interesting. I am trying to do exactly the same thing for the volume of water within a certain temperature range in the Gulf of Alaska. So far I have had no luck making that calculation with the 3D interpolator. Joe Breman may be able to give us a better idea of whether this is possible - but my understanding is that it primarily calculates 3D TIN's - not true volumes. JOE: You may want to look into the Groundwater data model and the Qhull work that Gil Strassberg produced. (Groundwater Data Model Application Tools)This tool creates a volume 'lense' from points, using a 3rd party software app, which also derives a numeric value. TIFFANY: Okay - the link Joe sent you is to an older version of the hydro tooklit. Newest link is at http://support.esri.com/index.cfm?fa=downloads.dataModels.filteredGateway&dmid=37. Neither seems to be fully functional upon first installation - I ended up installing both. You will need to read the documentation for help on setting Qhull. If anything goes wrong while you are setting this up, it seems to make the menus unusable. I found reloading from the original file or doing a RESET in the install menu solved the problem. When I then ran the demo of the convex hull from 3D points tool, it kept looking for code. The CODE directory is not in the older version of the program, but is in the newer version. I finally just created a C:\Gil\Code\GWToolbarNew\ directory and copied the contents of the code directory in the newer version of the toolkit there. At this point I can corrrectly run the tool and get a volume. To get what you want, I would load your oxygen data, use "choose by attribute" to select the points with the o2 values you want and build a convex hull of them. Then use the "convex hull from 3D points tool" to calculate a volume. One gotcha is that the X/y and z dimensions will need to be in the same units. I tend to store x/y in degrees and z in meters, which casues odd results for this kind of thing. I like the Antarctic project you sent. Very cool. And I had forgotten that we had actually calculated volumes in the second reference you sent - how quickly one forgets old projects. Thanks for the reminder. We do still have C-Tech - just not enough time to really use it.