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.

[EricRice]

If the workspace is a folder, then you are writing an Esri GRID raster. If the workspace is a geodatabase, then you are writing a geodatabase raster. Neither would require you to specify an extension with the name.

Are you sure you aren't mixing different units of data when creating the mosaic? Often I see a line like yours when people mosaic data that is in feet with other data that is in meters. If you identify a pixel on either side of the black line is one ~3x bigger than the other?

Best,
Eric

[bernardfoong]

Hi Eric,

Thanks for your reply.

How do I check if the mosaic data is in feet or meter? Do I go to the Layer Properties of the raster and get the raster information under spatial reference? If so, the linear unit is given as meter (1.000000). If this is not the way to find it, how do i verify?

No, the black portion is 3 times smaller.

Thanks,
Bernard

[EricRice]

Bernard,

The linear unit has to do with coordinate system (X,Y) units, not the pixel (or Z) unit. You have to know this (local knowledge of terrain), if it is not in any metadata. There is nothing in the layer properties for the unit of the pixel - many rasters, like a landuse raster don't have a concept of units. Unless there is a giant cliff, two pixels on either side of the black seam shouldn't be 3x smaller/larger. It basically confirms that your are mosaicking data with different units. You have to pick a unit, convert any rasters that are not in that unit by multiplying by the correct unit conversion factor, then mosaic.

Best,
Eric

[bernardfoong]

Hi Eric,

Thank you for your explanation. It was clear and I understood it.

If that is the case, can you guide me on how to multiply the raster on a guide-by-step basis? I still new to the software.

Thanks,
Bernard

[EricRice]

You need 3d analyst or spatial analyst.  There is a tool called Times in both of them.  Input your raster and multiply it by the unit conversion factor.  It's a really straight forward tool, but let me know if you have any questions.

Best,
Eric