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This might be a very simple question - but it is quite vital and I want to make sure I am thinking this through right.

I have used the cut/fill tool to calculate the difference in volume of a volcano cone. I have an attribute table, is it just a case of adding up all the -ve values to find the overall volume? (negative because the volcano has inflated i.e. I should be gaining volume).


So, This is an example of my attribute table. However, I think that I actually need both the negative and the positive values. So, are you saying that I would have to do (2*-110676.30...)+(1*17935.13...)+(1*-55080.16...)+etc?

Volume attribute table

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Provided your Z units are the same as your X and Y units:

You have it almost right. Adding the negative values would give you the total volume of the increase. HOWEVER, this would only be your answer if there were no POSITIVE values in the resulting attribute table. (If your resulting rendered shows any red and no blue areas) What this means is that although the volume of the surface has increased in some areas, it has also decreased in other areas. You must consider both numbers to calculate total gain.

Positive values for the volume difference indicate regions of the before raster surface that have been cut (material removed). Negative values indicate areas that have been filled (material added) See more here.

The tool finds differences between 2 surfaces. Add up all positive records to get a total volume decrease between the 2 surfaces (or cut - volume removed). (The results renderer will display cut areas as blue)

Add up all the negative records to get a volume increase between the 2 surfaces (or fill - volume added). (The results renderer will display unchanged areas as red) The number is negative = merely an indicator that this number represents fill

in areas where material has been cut, the volume will be positive (larger value - smaller value > 0). When material was added, the volume will be negative (smaller value - larger value < 0).

If your surfaces are similar and most of the area has not changed you will have a volume of 0 and a large cell count for those areas. (The results renderer will display unchanged areas as grey)

Provided you are using metric system and your units are metres the volume is in m3.

the negative value of fill is merely an indicator of the volume being a fill so the the renderer can display it correctly:

Turn the negative FILL total to positive and subtract:

Subtract FILL - CUT = CHANGE in Volume

positive result will mean there was an overall volume increase between the 2 surfaces and the final number will show by how much it increased (total fill - in m3 if you are using metric and metres as units)

negative result will mean there was an overall volumen decrease between the 2 surfaces and the final number will show by how much it decreased (total cut -in m3 if you are using metric and metres as units)

enter image description here

EDITED:

There seems to be a confusion as to what the ESRI example shows. To clarify, lets look at it in 3D and give it actual values:

enter image description here

Each cell is 10m x 10m

Each cell in the entire Before_Ras has an elevation 30m):

enter image description here

2 of the cells in the After_Ras have an elevation of 28m and 1 cell has an elevaion of 30m: enter image description here

2 of the cells whose a combined area of 200m2 are 2m lower then the Before_Ras and their combined volume is therefore 200m2 x 2 = 400m3)

1 of the cells whose area is 100m2 (10mx10m) is 5m higher then the Before_Ras and it's volume is therefore 500m2x5 = 500m3

The resulting difference WRT volume increase or decrease between the 2 surfaces is therefore: FILL - CUT = 100m3 (an increase off 100m3): enter image description here

enter image description here

The 13 other cells whose combined area is 1300m2 remain unchanged as you can see in the resulting attribute table in this example:

enter image description here

Credits: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z000000tz000000.htm

http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/How_Cut_Fill_works/009z000000vt000000/

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On the ESRI example page for the cut/fill tool for ArcGIS 10.0 it appears that you need to multiply each volume column by its count and then add that to the other records after performing the same operation on them to get the actual amount of change. Each record contains all of the results cells that had the same volume change. Looking at their attribute table you would get a volumetric change of -300.

The 1 * 500 for the 500 record of cells with + 500 change and 2 * -400 for the record of cells with -400 change. Adding this together (500 + (-800)) would result in a volumetric change of -300; whichever units their example is in.

To accomplish this you will:

  • Create a new field. Say it is called TotalVol
  • In the field calculator, multiply Count by Volume with the following equation/syntax:

    [Count]* [Volume]

  • Get the sum of your newly calculated TotalVol field (there are a number of ways to do this the easiest is probably to just right click the field and choose Statistics. In the resulting Statistics window is a Sum attribute which will be the net volumetric change.

If looking at volumetric change is something that you do a lot of, I would encourage you to look into the Geomorphic Change Detection (GCD) Software. Depending on what version of Arc you use it has a plug-in version and an Add-In version. The issue of estimating volumetric change is made much more complicated by the making sure rasters are orthogonal and concurrent as well as accounting for uncertainty in the raster values. GCD puts all of these tools in one place for you, is very well documented, and provides different methods to report your results.

  • I believe you are not correct. The net loss (400) is already a sum of the 2 cells. NO need to perform any further calculation. The resulting change (in this case increase) is 100. – Jakub Sisak GeoGraphics May 23 '14 at 14:53
  • Do you know if your right Jakub, and that the volume has already been 8 by the count? This would make my answers seem fair more feasible, as when I do as described as above (i.e. count * vol) I end up with huge volumes. – Katie C May 28 '14 at 15:46
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If you want to calculate the sum of cut and the sum of fill do the following:

  1. Go to the attribute table of the layer
  2. Sort the rows by volume
  3. Select the rows with minus (i.e. fill) (highlight them)
  4. at the bottom of the window you can click on 'show selected records'
  5. Click on the VOLUME column id and click 'statistics'
  6. Here you will have the sum for all the FILL rows.

Do the same for CUT values if needed.

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