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If I have an existing Surfer grid file (not one gridded with a log transform), can I still display it with logarithmic contour levels?

Yes, you can display any grid created linearly (e.g. a grid file created in a version of Surfer prior to version 12 or one created with a Z Transform set to Linear) with the contour level method set to Logarithmic.  Simply select the Contours layer in the Contents window, and in the Properties window, click the Levels tab and set the Level method to Logarithmic.

 

Depending on the Z range of the grid, that could give you a similar result to a map created from gridding the data with the Z Transform set to Log, save as linear with logarithmic contour levels, but not quite the same.

 

By gridding the data linearly, some of the extreme low and high values may have already been smoothed over. In addition, any negative or 0 values in the linear grid cannot be displayed with logarithmic contour levels and so extra steps should be taken to convert the negative or 0 data to a number >0.0.

 

Displaying a grid created with a linear scale as a contour map with logarithmic contours may be sufficient if you do not want to regrid the data or do not have the original data to regrid; but if you have logarithmically distributed data, it is most accurate to grid the log of the data.

 

See also:
Displaying Logarithmically Distributed Data in Surfer

 

Updated October 20, 2017

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