Surface Area and Volume Calculation-unit details

[SeathSelvan]

In the 3D Analysts Tool-'TIN Polygon volume' function is there. In that, i have given all the required files. The output gives Surface Area and Volume informations.

I have two questions
1. What is the unit of the output(Surface Area, Volume), Any details available regarding that

2. I have calculated the Area of the Polygon(Input Feature Class) using calculate geometry.
    When comparing 'Area' with the 'surface area', surface area is less than the area. Why it is like that

Can anyone help me to clarify this
Thank You

[MichaelStead]

I think that is physically impossible, so I would expect some error in the TIN or that the reference plane is below (or above depending on the analysis) than the top elevation of the tin in the polygon areas that are giving this result (so only part of the area is being summarized in the surface area field).

I would add a new field in my polygon layer and calculate it to equal some value higher than the highest value in the TIN. Repeat the calculation using this value for the reference plane field and see what you get for surface areas. This will give you garbage for volumes, but depending on what you are doing the volumes may be useless anyway. These are volumes from your surface to a height plane, this is ok for a lake or maybe a soup bowl, but you may need to do a cut/fill or something depending on what your surfaces look like.

[JamieDrisdelle]

The unit of the output is in whatever the unit of the spatial reference of the TIN is.  So if it is in a UTM zone it is in m^2 and m^3.