+ Reply to Thread
Results 1 to 4 of 4

Thread: 3D Analyst/Surface Analyst/Area and Volume Statistics inconsistent why!?

  1. #1
    Scott Atherton
    Join Date
    Apr 2012
    Posts
    2
    Points
    0
    Answers Provided
    0


    0

    Default 3D Analyst/Surface Analyst/Area and Volume Statistics inconsistent why!?

    I am using ArcMap 9.3.1, 3D Analyst/Surface Analyst/Area and Volume Statistics to calculate some statistics on a TIN we have for a lake. The two options for calculating statistics are “Calculate Statistics above plane” and “Calculate Statistics below plane”. It says my Z max is 14.19 and my Z factor is 1. When I enter my Height of plane as 0 and calculate the statistics above the plane it gives me these results:
    Click image for larger version

Name:	1.jpg
Views:	121
Size:	80.2 KB
ID:	13472
    And when I enter my Height of plane as 14.19 and hit calculate statistics below plane I get these results:
    Click image for larger version

Name:	2.jpg
Views:	90
Size:	75.5 KB
ID:	13473
    These numbers should be the same should they not be? am I missing something here? Any explanation would be greatly appreciated,
    Thanks in advance!

  2. #2
    Jeff Swain

    Join Date
    Nov 2009
    Posts
    749
    Points
    184
    Answers Provided
    21


    0

    Default Re: 3D Analyst/Surface Analyst/Area and Volume Statistics inconsistent why!?

    Please take a look at this help documentation on Surface Volume. When you are changing the plane, then you have to consider what is being asked. The reason your values are different is that there are vastly different areas being surveyed depending on your data.

    Click image for larger version

Name:	SVolRPabovePlanebelow.png
Views:	79
Size:	89.7 KB
ID:	13485Click image for larger version

Name:	SVolRPbelowPlaneabove.png
Views:	85
Size:	95.0 KB
ID:	13486
    Esri Education Specialist
    Esri Certified ArcGIS Desktop Professional
    Training Services
    Esri Training | ArcGIS Ideas

  3. #3
    Scott Atherton
    Join Date
    Apr 2012
    Posts
    2
    Points
    0
    Answers Provided
    0


    0

    Default Re: 3D Analyst/Surface Analyst/Area and Volume Statistics inconsistent why!?

    Thank you for your response, Ok that explains why the area and volume are different, what I was really struggling with was why is the 2d surface area not the same. When I calculate these statistics for the lake (depth expressed in positive numbers) the plane would be set to 0 and I would be “calculating above the line”, however, that 2d surface area does not match up with the area calculated with the field calculator, it is the “calculate below the line” 2d surface area that matches up with the field calculator. In the image you posted above the blue line would represent your 2d surface area and it remains consistent regardless of the above/below calculation, or am I mistaken on this point?

  4. #4
    Jeff Swain

    Join Date
    Nov 2009
    Posts
    749
    Points
    184
    Answers Provided
    21


    0

    Default Re: 3D Analyst/Surface Analyst/Area and Volume Statistics inconsistent why!?

    Ok so that I am following along, you are comparing the 2d Surface Area did not match the calculated geometry of the shape, the raster was built on? But only for the 'below' calculation, not the 'above.' Is that correct?

    In the screenshots, the plane height is changing so it will definitely not match. I would believe if you have selected 0 for the height in each case the 2d area should match, but will not if you change the plane height, since the cross section you are comparison will change.
    Esri Education Specialist
    Esri Certified ArcGIS Desktop Professional
    Training Services
    Esri Training | ArcGIS Ideas

+ Reply to Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts