topic Re: Mosaic to New Raster in ArcGIS Spatial Analyst Questions

Mosaic to New Raster

SarahNiemczura — Thu, 24 Jul 2014 15:24:39 GMT

Morning Everyone,

I'm currently working on creating datasets with a uniform extent. This means some of the datasets I have need to be clipped down, and some need to grow and incorporate no-data fill values.

How does one go about this? I cannot seem to get a raster with an extent of -19,38,52,-36 to change to a raster with an extent 90,-180,180,-60.

Any thoughts on how to go about doing this?

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 15:30:25 GMT

Set the desired extent in the Environments tab of the Copy Raster tool and create a new raster of the desired extent. You cannot change the extent of an existing raster, you can only create new ones that meet your criteria

Re: Mosaic to New Raster

SarahNiemczura — Thu, 24 Jul 2014 15:48:30 GMT

Hi Sol,

Good idea.

I have to essentially have the rasters have the same starting point for someone who wants to use these in MatLab. So the Chirps and Hain ET need to have the same extent and UL as the MODISET. Does that help?

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 15:55:13 GMT

what coordinate system/projection are your tiff files in?

Re: Mosaic to New Raster

SarahNiemczura — Thu, 24 Jul 2014 16:03:18 GMT

GCS_WGS_1984

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 16:09:45 GMT

Possible issues...One of them isn't or it has been defined incorrectly, or they differ in extent. If it is the latter, then there is nothing you can do since the coverage is what it is. Reporting on the 3 file extents would be useful as well projection information.

Re: Mosaic to New Raster

SarahNiemczura — Thu, 24 Jul 2014 16:14:56 GMT

MODIS ET extent is 90,-180,180,-60

CHIRPS extent is 50, -180, 180, -50

HAIN extent is 37, -18, 553, -40

I'm guessing it's the, there's nothing I can do option.

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 16:17:46 GMT

Even if you confirm the extents are what they are, your options are
1 to live with it
2 clip two of the files down to the smallest of the files

Re: Mosaic to New Raster

SarahNiemczura — Thu, 24 Jul 2014 16:21:09 GMT

Just realized my MODISET was undefined. Going to have it match the other coordinate systems GCS_WGS_1984 and see if that helps. UGH! It's always been something stupid lately...

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 16:26:56 GMT

I said the smallest...I suspect that the files are of different extent which means the larger ones need to be clipped down to smaller ones. Sarah you still need to check the extents to be certain, it is quite possible that defining the projection will still not result in what you want. As a check, you should really add each layer into its own data frame and have a visual look, then add the other ones in one at a time. The coordinate system of the data frame is established by the first file added to it...which can have unforeseen consequences. Good luck

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 16:34:24 GMT

Only if the file is saved to a new one

Re: Mosaic to New Raster

SarahNiemczura — Thu, 24 Jul 2014 16:44:47 GMT

I have tried that, copy raster and raster to new mosaic using the environmental settings extent to the 90,-180,180,-60 and it doesn't create the no data values to fill the extent. Yes I do save them to a new file.

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 16:48:01 GMT

did you determine the actual extents of the files? Did you try some of the other suggestions?

Re: Mosaic to New Raster

DanPatterson_Retired — Thu, 24 Jul 2014 16:49:42 GMT

Sol...the environment settings should be set in the Environments tab for each tool used in Arctoolbox...there are many cases where the general raster settings were not honored by the tools

Re: Mosaic to New Raster

MikeBallard — Fri, 25 Jul 2014 17:08:56 GMT

Have you tried running ypur rasters through the raster calculator? You can set the desired output extent, and coordinate system. Ypu might also try the raster snap option too, which I believe will ensure each raster starts at the same coordinate position. You can have one input and one output raster. Failing that I would create a new "allones" raster of the desired dimensions and values all = 1, and in raster calculator try input raster * allones = desiredoutput.

Re: Mosaic to New Raster

SarahNiemczura — Fri, 25 Jul 2014 17:18:15 GMT

How would one put the coordinate system and extent into raster calculator? I'm not familiar with that.

I did however come up with a work around in case I can't find any programming; I've made a model that will copy out the raster in the proper extent, copy will then be * 0 to make it blank, I will then mosaic the smaller rasters to the copy. Tedious but it's a fix for now.

Re: Mosaic to New Raster

MikeBallard — Fri, 25 Jul 2014 17:44:46 GMT

These Environment settings all effect the output of raster calculator. You can set environments before running raster calculator:

Cell Size, Current Workspace, Mask, Output Coordinate System, Extent, Scratch Workspace, Snap Raster

http://resources.arcgis.com/en/help/main/10.2/index.html#//001w00000034000000

Your workaround sounds like a normal approach. The basic concept for geoprocessing is input> tool> output. Moat often they way to 'change' data is to process it into a new form.

Mike Ballard, Professor

Geographic Information Systems

Algonquin College

http://lyceum.algonquincollege.com/roomfinder/index.html?poi=t336b

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