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Jeremy Haynes

refining solid model - null values or 0?

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Hi,

this is a revisit of an age old problem, but I'm modelling contaminant concentrations, and they are extending to the bottom of the model where there is not a data point to constrain the model. I generally use the detection limit as a lower limit, but is using a null value better?

Thanks,

Jeremy

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Hi. I face a similar problem when I map down hole clay samples. I have found that entering 0s works when what I want is a 2D log but if it is 3D then simply omitting values where there is no detection best. It really depends on how you want to display the data. However I would like to know what the optimum method is from an experienced Rockworks user.

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Hi Jeremy and Edward,

Using low values or zeros can help to constrain a model if you add them in all areas of no data. If there is no data, the algorithm is free to extrapolate the model based on the other values in the model.

Null values are used in the model to indicate areas of no data, but null values in the data act like real data values.

You may want to clip the solid model with a gridded surface or with the total depths of the boreholes.

Every data set is different, and different methods work for different data.

Regards,

Tom B

RockWare Inc

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Thanks Tom,

Just to clarify, if I put null values (i.e. typing "null" as a replacement for "ND") into my data sheet, then that acts as a real value that constrains the extrapolation (or interpolation as the case may be)? Can I use the word null or do I need to enter the "null" number?

Thanks again

Jeremy

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Hi Jeremy,

In a datasheet, the letters "NULL" or "ND" are ignored and treated the same as a blank cell. The RockWorks null value -1e27 acts as a real numeric value causes RockWorks to hang, due to it being used as the null value in grids and solid models.

In the Borehole Manager, only numeric values are allowed in the I-Data and P-Data tables.

Regards,
Tom B

RockWare Inc

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Hi Tom,

I'm revisiting your explanation of the null value. If I understand you correctly, you're saying that use of the "null value (-1e27)" in the data sheet causes rockworks to "hang". Does this mean that one should not use the null value in the data sheet to represent a number? As an alternative, possibly "0" is better as a represents a "real number"?

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Hi Jeremy,

Yes, you are correct when you state that you should not use the NULL value in the worksheet.

The value that you use will depend on your needs. If you wish to constrain the data you can enter zero values.

Regards,

Tom B

RockWare Inc

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