Why the raster dataset doesn???t appear at smaller scale?

Question

Original User: Jamal432@gmail.com

Why the raster dataset doesn�??t appear at smaller scale?

Please, see the attached screenshots that show my question

I�??m wondering why the dataset shown in the screenshot doesn�??t appear at scale 200,000 while it appears at scale 150,000 knowing that the scale range isn�??t set

What might be the reason?

Thank you in advance,

Regards

Jamal

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Anonymous User · Answer

Original User: erictrice

Hi Jamal,

1.  Raster Catalogs and Mosaic Datasets can be used for managing very large collections of imagery, on the order of 1000's of TB's.  With this in mind they were created with some built in visibility rules, so as to avoid the display hit (performance issue) one might take while trying to render so much data at one time.  Because a single raster datasets size is highly unlikely to exceed that of a medium/large raster catalog or mosaic datasat, it doesn't need to have built in restrictions for displaying it.

2.  I'm not sure I understand the issue you describe.

3.  Raster datasets within raster catalogs can be managed in two ways by the file and personal geodatabases: either managed by the geodatabase or not.   The default behavior is that the datasets are managed by the geodatabase.  This means that when you load the catalog, the input rasters are converted and stored inside the geodatabase.  If you chooose to not have the geodatabase managed the data, you select "Unmanaged" for the Raster Management Type parameter in the Create Raster Catalog tool.  What this means, is the source rasters will be referenced from their original location and no data conversion or loading will ocurr.  Mosaic datasets do not give you a choice; they are always unmanaged in the sense that they just point to the real data.  If you change your catalogs in the future to be unmanged, they will load a lot faster and be more on par with what you see when loading a mosaic dataset.

4.  I believe Melanie answered this question in another forum thread you posted it in.  Nonethelss, nothing about the resolution is changing.  It appears to be related to statistics and stretching.  Did you try what she suggested?  i.e. Settting the stretch type to None.  If you zoom all the way in do they look the same?

JamalNUMAN · Answer

Jamal,

You are working with a mosaic dataset, not a raster catalog.  Please review the documentation on mosaic datasets, specifically the section on mosaic dataset overviews.

These should also help guide you.
The workflow and tools to create mosaic datasets

Imagery: Data management patterns and recommendations

Your data appears to be somewhat high resolution.  At 1:200,000 what will you get by looking at the image at that scale?  If you'll never actually look at the data at 1:200,000 then don't bother building overviews.  Only take the time to build them if it's appropriate to do so, or if you just want to see something at all scales.

Regards,
Eric

This is very helpful. Many thanks Eric

1)why disappearing of the rasters at certian scale occur for the Raster Catalog and Mosaic Rasters but not for the Raster Datasets themslves? (see the attached screenshots please)

for example, the Mosaic Dataset disappears at the scale of 250, 000 while the Raster Datasets don't

2) I couldn't distinguish accurately between loading the existing rasters to: Raster Catalog, Mosaic Dataset and Raster Datasets.

Based on what we choose to load our Rasters to: Raster Catalog, Mosaic Dataset or Raster Datasets?

3) why does it take so much time to load the rasters to Raster Catalog while it takes little time to load it in Mosaic Dataset?

4) why loading the rasters to Raster Catalog produces "Coarse" raster while loading them in a Mosiac dataset produces "Clear" raster similar to the source raster?

appreciated

regards

Jamal

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Anonymous User · Answer