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Contour Maps (Calculate Volumes)

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I need help with calculating volumes for a gravel deposit. I have an original contour surface drawn from 2006 and a new contoured surface for 2008. I need to be able to show the differences between the two on the drawing (e.g. -12m etc..) and then be able to calculate what volume of material has been moved out of the pit since 2006. :blink:

Anthony

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Hi Anthony,

Do you have the original grids or just the contours? Its much easier to calculate volume changes from a grid, you only need to create the new one with the same node spacing and size and then use the Grid Math functions in the Utilities.

If you only have contours you'll need to digitize them either using a digitizing tablet (Didger) or on screen (RockPlot2D) to get the volume changes. Creating a correct surface grid from contours is surprisingly hard to do.

Mitch

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I am really new at using Surfer and I am not sure how to make a grid. Is it just a grid map as I do have all the original survey data including elevations from 2006 and the most up to date survey.

I would appreciate it if you could help me learn to make grids or point me in the direction to find out how to do it.

Anthony

Hi Anthony,

Do you have the original grids or just the contours? Its much easier to calculate volume changes from a grid, you only need to create the new one with the same node spacing and size and then use the Grid Math functions in the Utilities.

If you only have contours you'll need to digitize them either using a digitizing tablet (Didger) or on screen (RockPlot2D) to get the volume changes. Creating a correct surface grid from contours is surprisingly hard to do.

Mitch

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Hi Anthony,

Mitch is talking about gridding the data. In Surfer this is done with the Grid | Data menu command. This command requires the data in an ASCII or Excel XYZ file format.

An example ASCII XYZ data file follows:

"X" "Y" "Elevation"

0.1 0 90

3.5 0 45

4.9 0 65

6.2 0 40

...

Grid the 2006 data file and the 2008 data file with the same XY min and max and the same number of grid lines. Then choose Grid | Volume to calculate the volume between the two surfaces.

If you have further questions, please contact me.

Thanks,

Tom B

[email protected]

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I finally figured out how to grid the data and how to use the two different grids (the upper and lower surface) to get a volume. My next question is: If the elevation is in metres then is the volume in cubic metres??

Anthony :blink:

Hi Anthony,

Mitch is talking about gridding the data. In Surfer this is done with the Grid | Data menu command. This command requires the data in an ASCII or Excel XYZ file format.

An example ASCII XYZ data file follows:

"X" "Y" "Elevation"

0.1 0 90

3.5 0 45

4.9 0 65

6.2 0 40

...

Grid the 2006 data file and the 2008 data file with the same XY min and max and the same number of grid lines. Then choose Grid | Volume to calculate the volume between the two surfaces.

If you have further questions, please contact me.

Thanks,

Tom B

[email protected]

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Hi Anthony,

Volumes are reported in the same units as the X, Y, and Z units. If all three are in meters, then the volume is cubic meters.

However, if the XY units are "non-Cartesian" like latitude and longitude, then the volume units are degrees * degrees * meters, and these can not be converted to meaningful units. Start off with the XYZ units all the same to get meaningful volume units.

Thanks,

Tom B

[email protected]

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