SLAMM Forum

General Category => Model Formulation & Parameters => Topic started by: Hartney on October 20, 2017, 03:29:43 PM

Title: DEM to ASCII conversion issue
Post by: Hartney on October 20, 2017, 03:29:43 PM
Hello,

I am having an issue when I convert my study area dem to ascii.  The elevation range/values are different following the conversion (see image You cannot see attachments on this board.).  dem_censustract is my original dem while dem_asc is the new file after conversion. I found one person mention a similar issue on another gis forum but the question was unanswered (https://gis.stackexchange.com/questions/240552/raster-to-ascii-changing-values?rq=1). Has anyone else encountered this issue? Is there a work around?

Thank you!
Title: Re: DEM to ASCII conversion issue
Post by: Jonathan S. Clough on October 23, 2017, 08:43:41 AM
I think the problem is that the ASCII DEM is treating 1.17e-38 as its NODATA value.  The GIS software is then not recognizing this NODATA value.  Try specifying a NODATA value of -9999 prior to conversion and this may solve the problem. 

Also, look at the header in the first lines of the ASCII DEM to see if that helps understand the problem (the NODATA value is defined there.)  The best way to do this is convert the file type to a TXT file and look at it in the Windows Explorer Preview pane (not Internet Explorer, just the Windows Explorer file manager).

Hope this is useful.