topic Resample NED DEM in Data Management Questions

Resample NED DEM

MargaretGarner — Sat, 06 May 2017 16:28:10 GMT

Ok, I'm new. I have downloaded NED 1/9 arc-second DEM tiles and mosaic'ed a DEM The cell size is 3.0864198e-005, 3.0864198e-005. I am having trouble resampling to a cell size to match other rasters I am using. Also, I need to match the number of rows and columns in each raster. Any ideas?

Re: Resample NED DEM

DanPatterson_Retired — Sat, 06 May 2017 16:30:25 GMT

Your cell sizes are in fractions of a decimal degree. Are you intending to work in a projected coordinate system? If so, then you should project the data to match your other projected data before you proceed.

Re: Resample NED DEM

MargaretGarner — Sat, 06 May 2017 16:45:35 GMT

Thanks, Dan. All rasters have already been projected in state plane (NC, meter).

Re: Resample NED DEM

XanderBakker — Sat, 06 May 2017 18:29:13 GMT

Hi Margaret, do you mean you resampled / projected the rasters? What coordinate system and resolution do they have now. Do they align?

Re: Resample NED DEM

MargaretGarner — Sat, 06 May 2017 20:47:24 GMT

Hi Xander. I used Project Raster to change the DEM coordinate system to NAD 1983 (2011) StatePlane North Carolina FIPS 3200 (Meters). The cell size, before and after projection, is 3.0864198e-005, 3.0864198e-005. I have a NWI shapefile in this coordinate system that I have to convert to raster, then to ASCII for input into SLAMM model. For the model, the number of rows and columns have to be the same for each files (that's where I'm ultimately going with this). When converting from polygon to raster, it doesn't work to to set the cell size for the output to 3.0864198e-005, 3.0864198e-005. I end up with 300 x 300 (default), which I have resampled down to 10 x 10, but that doesn't get me where i need to be. I apologize for my inexperience, and appreciate any help I can get with this!

Re: Resample NED DEM

DanPatterson_Retired — Sat, 06 May 2017 21:16:51 GMT

3.0864198e-005 is 0.0000308 m ... Unless you are working on a hugely microscopic scale, I venture this is still in decimal degrees.

Can you confirm what the exact coordinate system was prior to projecting?

You did use the Project raster tool and not the Define projection?

Something is still amiss

Re: Resample NED DEM

MargaretGarner — Sat, 06 May 2017 23:01:12 GMT

The original coordinate system was GCS_North American_1983. I used Project Raster, not Define Projection. I have attached a page with screenshots from the layer properties on the initial mosaic before projecting (and clipping). Thanks!.

Re: Resample NED DEM

DanPatterson_Retired — Sat, 06 May 2017 23:17:23 GMT

Yes that is the unprojected version. What does the projected cell size and extent look like? What cell size did you use?

Re: Resample NED DEM

MargaretGarner — Sat, 06 May 2017 23:55:54 GMT

Projected info attached. (The raster was also clipped) In the Project Raster tool, selecting cell size is optional so I ran it without selecting.

Re: Resample NED DEM

DanPatterson_Retired — Sun, 07 May 2017 00:14:51 GMT

Well something went wrong since the raster extent and cell size are still in decimal degrees .

When using the Project raster tool, click on the Environments tab on the bottom right of the dialog and go to the raster section and set the desired cell size and other parameters appropriate to your situation, particularly if you are trying to align the rasters to other projected rasters (ie snap raster etc etc). When you have projected the raster, Insert Data Frame and add the newly projected raster to ensure that it hasn't been contaminated by the presence of other data and check the extents and everything again.

Re: Resample NED DEM

MargaretGarner — Sun, 07 May 2017 00:18:52 GMT

I'll try it! Thanks for taking the time to help me with this

Re: Resample NED DEM

DanPatterson_Retired — Sun, 07 May 2017 00:30:11 GMT

no problem... good luck