Image problem when mosaic to raster

[bernardfoong]

Hi,

I have mosaic several DEMs to a raster but I have encountered a problem whereby the output raster produces an image where one portion has additional black layer on it. I have attached the image in this post.

Please help. I have spend a lot of time trying to solve this. As I am very new to this software, I would really appreciate if anyone could give me a step-by-step guidance with this.

Many thanks in advance.

[ShaunLam]

What process are you doing to mosaic ?

Maybe try creating a gdb and a raster catalog, load the catalog with your DEMs then use the raster catalog to raster dataset tool.

In ArcCatalog, right click > new > file/personal gdb.
right click the file/personal gdb you just created, > new > Raster catalog.
right click the raster catalog you just created > load > Load raster datasets... load your datasets.
once completed in the toolbox, Data management tools > Raster > Raster dataset > raster catalog to Raster dataset

Hope this helps.

[bernardfoong]

Thanks for your reply.

I want to merge the DEMs that I downloaded and merge them into raseter in Arcgis. I intend to model the hydrological flow of the region.

I tried using the catelog and the gdb but i get the same result. Is there out solutions to smoothen the raster?

Thanks again.

[ShaunLam]

Are the DEMs overlapping ? is that what that black shade is ? the picture you uploaded is ridiculously small.

You can always try clipping the DEMs so that there is no overlap. Then running the process over.

If you have spatial analyst you can use the extract by mask tool to clip the DEM to a footprint.

[bernardfoong]

Hi shaun,

Many thanks for replying.

I am not sure why is there a dark shade. It happens when i mosaic all the DEMS together in Arcgis "moasic to to new raster" function.

How do I check if the DEMs overlap with it each other? I cant find the mask tool in spartial analyst. I am using version 9.3.

Can you give me a step-by-step approach as this is my first time using this software.

Thank you.

[ShaunLam]

It shouldn't matter if they are overlapping using mosaic to new raster or the raster catalog option.

What output extension are you trying to use ? Try use the default Esri Grid.

[bernardfoong]

The output I am trying to get a .aux file for the merged raster which i think is the default esri grid.

[ShaunLam]

So under raster dataset name with extension you aren't putting any extensions ?
How big are 2 of the tiles that show the black shade, are you able to send to me ?
shlam@golder.com.au

You can always try with smaller dataset to speed up the process.
Extract by mask is under spatial analyst tools, extraction, extract by mask, or just use the index or search tab under the toolbox and type it in.

[ShaunLam]

The output I am trying to get a .aux file for the merged raster which i think is the default esri grid.

I just re-read that, when you use the Mosaic to new Raster tool, Under "raster dataset name with Extension"
are you putting in there "filename.aux" ?

[bernardfoong]

under raster dataset name with extension I did not put any extensions. Is this the source of error?