Mosaic datasets: Pyramids AND Overviews?

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06-08-2011 10:01 AM
LisaShertz
New Contributor III
I am planning my storage needs for a new aerial photography set. I am planning to use mosaic datasets. One of the things that I am confused about (and there are several others) is about pyramids and overviews.

From the documentation it appears that I need to make both pyramids and overviews; aren't they doing the same job? Does this mean that I am building 2 resampling datasets (3 if you include caching for internet maps)? Do I need to do both?

Any explainations, comments adn experiences are appreciated.

LIsa Shertz
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5 Replies
ThomasDilts
Occasional Contributor III
There are some slight differences.  Overviews appear to be calculated at coarser extents.  They basically take over where pyramids leave off.  Also, overviews are stored differently than pyramids.  I realize now that using a mapped drive is a big mistake with the mosaic dataset, because my data isn't visible on my other computer (I didn't use UNC).  However, the overviews are visible and the GIS service created from the mosaic dataset is visible.
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GordonSumerling
Esri Regular Contributor
Hi Lisa,

Pyramids are internal to each image and relate specifically to the image. An overview is the smaller resolution images that cover the entire dataset. These are external to the source images and in effect "join" adjacent images together. These are stored next to the file geodatabase sepeate from the original imagery. This is where the mosaic datset gets it speed from.

You do need both to get the optimal speed from the mosaic dataset.

HTH

Gordon
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EricRice
Esri Regular Contributor
Lisa,

Overviews are generally faster than pyramids so you don't need both of them for optimal speed.  If your data comes to you with pyramids, great, we will use them (and write fewer overviews).  If you don't have them, we will simply build more overview levels.  There are specific use cases for building pyramids on the source rasters though.  I recommend reading Mosaic dataset overviews in our product documentation for more insight.

Best Regards,
Eric
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JoeBryant2
Occasional Contributor II

In an effort to help others who find their way to this post and are wondering if they need to use both Overviews and Pyramids in their mosaic dataset, I can share what the deciding factor was for us:

When building more complex mosaic datasets, especially where you will be taking advantage of the mosaic methods and on-the-fly processing, then it can be advantageous to build pyramids on the source rasters and to build overviews only where they are needed, such as when

  • The mosaic methods will be used due to overlapping imagery

Our orthophotography tiffs DO overlap, and therefore need to take advantage of mosaic methods. Because of this help document, I decided to use BOTH pyramids and Overviews.

I hope this helps someone else, too!

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LisaShertz
New Contributor III
Thanks everyone for your answers, they have been helpful.

Lisa Shertz
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