Importing Esri ASCII Grids with NoData values

[aorr]

I've been trying to extract a surface from another surface in order to "erase" part of an aquifer surface that was modeled above a ground surface I created. After being unable to get this to work using the RockWorks Utilities I decided to do it in ArcGIS which I'm more familiar with.

This has lead me to a new problem though. When I export my new grid from ArcGIS I have "NoData" values set to -9999 as per the format the original surface was exported with (there were a few holes in that surface which used this as a NoData value so I did the same with my exported grid).

When I import my new ESRIGrid into Rockware it doesn't seem to recognize the NoData attribute and instead draws the surface for those cells at -9999 feet in elevation.

How can I specify that it ignore those and make those values invisible for the surface?

(I've attached a screenshot showing the files I'm refering to above. The top text file is an original export that has some NoData values from RockWorks in it. The file below is a file I've imported and it is rendered in the graphic incorrectly. RockWorks does draw the NoData values)

Thanks for the help,

-Andy

[aorr]

Another option that I could do in order to fix this issue I mention above, would be to run an operation that re-assigns all of the values of -9999 to a null/nodata value.

I've experimented with the Grid Range Filter but it doesn't seem to offer setting a value to "nodata" or "null" in order for it to not appear in the grid.

-Andy

[Molly]

Hi Andy,

First, I think we should be able to get the Utilities to constrain one grid with another, eliminating the need to use ArcGIS. This Utilities | Grid | Filters | Limit filter does require that both grid models have the same extents and node spacing. You can use the Grid | Math | Resample option to resample either grid (or both grids) to the current output dimensions.

If you want to stick with your imported ESRI ASCII grid, you should be able to use your second suggestion - the Utilities | Grid | Range filter will allow you to activate a Low-Stop filter for all values less than -9998 and replace them with NULL. See my attached screenshot.

Let us know if you have additional questions.

Molly Mayfield

RockWare Inc.

[Molly]

forgot the attachment !

[aorr]

Molly,

Thank you for your feedback. I will try again to use the Utilities in order to constrain the grids. Hopefully I can get that to work. I'm 100% confident it's just my lack of understanding the RockWorks workflows yet and I'm missing a key procedure.

Since writing my 2nd post, I was able to use the Range filter and assign values to Null. I just wasn't familiar with how to enter "null" into the field. Turns out it's very simple after all.

Thanks for your help,

-Andy