topic Re: Converting DEM cell size from degrees to meters in Data Management Questions

Converting DEM cell size from degrees to meters

DavidWampler — Mon, 16 Dec 2013 17:45:31 GMT

I have a large DEM dataset of the world's landmasses. The cell size is currently 1 arc-second. I need to resample the cell size to 250 meters. I can't for the life of me find out how to do this, but I need to in order to match it up with the cell size of other rasters I am using (which will make it easier to run some custom tools on them after converting to ASCII).

Is this possible to do? I understand there will be some error involved converting from degrees to meters, especially at higher latitudes, but since I'm converting from ~30 meters to 250 meters I assume that won't be much of an issue.

Re: Converting DEM cell size from degrees to meters

NeilAyres — Tue, 17 Dec 2013 05:05:14 GMT

You need to project your data from GCS to a flat projected coordinate system.

http://resources.arcgis.com/en/help/main/10.2/index.html#//003r0000000q000000

Your biggest problem here will be to select a suitable PCS for your analysis.
This will depend on what you are doing with the data.

You may have to consider splitting up the data into continental sized bits and projecting each one separately.

Cheers,
Neil

Re: Converting DEM cell size from degrees to meters

larryzhang1 — Tue, 17 Dec 2013 05:41:21 GMT

I have a large DEM dataset of the world's landmasses. The cell size is currently 1 arc-second. I need to resample the cell size to 250 meters. I can't for the life of me find out how to do this, but I need to in order to match it up with the cell size of other rasters I am using (which will make it easier to run some custom tools on them after converting to ASCII).

Is this possible to do? I understand there will be some error involved converting from degrees to meters, especially at higher latitudes, but since I'm converting from ~30 meters to 250 meters I assume that won't be much of an issue.

David,

Straightforward to use GP tool called �??Project Raster�?? at http://resources.arcgis.com/en/help/main/10.2/#/Project_Raster/00170000007q000000/ . However, we users don�??t see the tool in 10.x (see the attachment).

Nevertheless, considering your DEM data using geodetic/WGS 84 (Z CS is �??WGS_1984_Geoid�??), advisable to use the following effective workflow in ArcGIS:[INDENT]

�?� Create MD with local projection (saying, UTM 15 with the datum NAD83 /WGS 84); here, the better practice is: to ensure your data source with �??Elevation�?? under �??General�?? and Z CS in Spatial Reference Properties referred to �??WGS_1984_Geoid�??;

�?� Load your 30-m DEM into MD;

�?� Export the desired AOI directly from MD as raster (TIFF, or IMG). Here, ensure �??cell_size�?? equal to 250-m (rather than 30-m);

�?� Convert into any other formats like ASCII, etc�?�[/INDENT]

Re: Converting DEM cell size from degrees to meters

SteveLynch — Tue, 17 Dec 2013 13:38:17 GMT

However, very sadly, we users don�??t see the tool in 10.x so far (see the attachment)[/INDENT]

Larry
In your graphic, what happens if you expand the tools in Raster. I.e

DataManagement->ProjectionsandTransformations->Raster->ProjectRaster

Steve

Re: Converting DEM cell size from degrees to meters

larryzhang1 — Tue, 17 Dec 2013 15:35:47 GMT

Larry
In your graphic, what happens if you expand the tools in Raster. I.e

DataManagement->ProjectionsandTransformations->Raster->ProjectRaster

Steve

Thanks�?Steve�?

Visible now after expending.

David,

You can try this GP (or the GP 'Resample') and then compare with the above MD workflow ...

Re: Converting DEM cell size from degrees to meters

DavidWampler — Thu, 19 Dec 2013 19:38:52 GMT

Thanks for the help - that got me on the right track. A second difficulty is that the projection I am using is not in the default list (MODIS Sinusoidal) - I should have mentioned that to start with. But, adding a custom geographic transformation for that did the trick. In the end, I got the cell sizes to match up perfectly!

For reference of anyone else needing to project into the MODIS sinusoidal, this page gave the required extra information:
https://code.env.duke.edu/projects/mget/wiki/SinusoidalMODIS

Although I only needed to follow a few of the steps there along with what was mentioned in this thread to get it to work.