How to use Local Raster Function Set Null?

Hornbydd

All,

Normally I use the geo-processing tools to complete the following task but I thought I would give the raster functions ago as they appear to be a quicker and smarter way of doing thinks, but I failed at the first hurdle!

I have a DEM and I want to set all  negative elevation values to NODATA, typically I would use the Set Null tool to achieve this.

So I started to create a raster function (see screen shot below) but I cannot work out how to complete this apparently simple task.

How do you complete the dialog to say "value < 0". I'm not understanding what the greyed out operation box is telling me? For example if one was to write this in python it would be:

outSetNull = SetNull("elevation", "elevation", "VALUE < 0")

Would someone post a screen shot of how to run the local function Set Null as a Raster Function?

Hornbydd

All,

Thanks for your help and especially Neil Ayres as his solution is basically a whole lot easier (see below)! With a second set of eyes looking over my shoulder we cracked this frustrating problem. Probably like Dan Patterson I'm used to using the geo-processing tools or scripting it and I was looking for a way to include the criteria part of the set null tool in the raster function, in my case the "Value < 0".

The short answer is you can't, it's not geared up to accept expressions. I had actually explored the approach I'm about to reveal but dismissed it as me making some mistake but it turns out there is a bug in 10.4.1 which I will explain.

So you need to create a boolean grid, in my case where elevation is less than 0, this is essentially the result of the criteria, then you chain that into the set null tool.

So the first raster function is Less Than Equal as shown below:

The output of LessThanEqual function feeds into the Set Null function along with the DEM for what will be the values used under a FALSE condition.

So the final function chain is this:

Now the bug is that ArcMap does not display this "on the fly raster" correctly. The symbology defaults to stretch using standard deviation. This should work but it does not as it is saying the value range is 0 to 1 when in my case it should 1m to 360m. So changing stretch type to min-max the values still stay at 0 to 1 even though it is showing the correct values in the mini statistics panel in the stretch panel. I had to tick on edit high/low values and manually set the min and max values then the raster displayed correct with everything below zero set to NODATA.

DEM showing cells in the sea (Value < 0) as NODATA