kriging results to raster

[AstridHarendza]

Hello,

I have a question regarding the export of kriging results into a raster. I've seen a few threads related to this question, but unfortunately could not find the right answer.

The problems:
1. The raster's min and max values differ from the min and max values of the input data.
Max and min values (which are actually real measured max and min) change by nearly 10% when the kriging result is exported to a raster, which is not acceptable for my data and study purpose. I've seen that this problem is linked to the cell size. Is there anyway around it - recalculating the raster values in some way and trying to correct them manually? I really need the min and max values to not be changed in my dataset.

2. The isolines of classes as shown in kriging do not match with the ones in the raster.
As far as I understand is the problem the conversion of the on-the-fly, hence fairly coarse, interpolated GA layer into a much finer raster. So I played around with the cell size and did notice that the result improved when increasing the cell size, but I didn't manage to match the output of the GA layer. I also read in a few threads that the coordinate system could be a problem, so I converted it from degrees to metre, but didn't notice any improvements. My sampling area is only 6m^2, so I guess this makes the degree problem neglectable. Any suggestions on how to improve the raster output if a fairly fine grid is required?

I need a raster output (ideally a fine grid) as I would like to perform further analysis on these data.

Any suggestions and tips on how to deal with this and hopefully improve the end result are highly appreciated!

Best regards,
Astrid

[VivianeFaria]

Hello all,
I'm trying to understand how the conversion from GA layer to raster works, but there is one thing that is not clear to me when I read this:
"This happens when the input point containing the max value does not fall in the exact center of an output grid cell. In such cases, the max value is weighted according to the distance from the cell center as well as nearby points".

I would like to know if the min and max values are calculated in different way for GA layer and raster. If I knew the cell size from GA layer and used it when I converted GA to raster, would it be possible to have a similar visual result?
I mean, how do I choose the best cell size when I generate the raster?

Thank you for you attention,
Viviane

[AstridHarendza]

Hi Viviane,

please have a look at Eric's post below - he gives a brilliant explanation to this problem. A GA layer is basically more a continuous surface of a function that takes an (x,y) location and returns a value. It does not have a set grid resolution as a raster has and the contours you see for the GA layer are just drawn from a very course grid, with the symbology based on min/max of the input points.

The visual difference between GA layer and output raster is simply down to the different contouring and symbology, but the values will be the same!! I at the end decided on a raster grid size, exported and classified the raster in a similar way as the GA layer (i.e. max min and class ranges) - it looks the same and the values are the same.

Hope this somehow helps.

Cheers,
Astrid