Advantages Publishing a set of imagery

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03-07-2019 06:47 AM
Robert_CraigAshby1
New Contributor III

What are the advantages of publishing a set of imagery as a mosaic data set versus. a cached imagery service in terms of availability, resource consumption? 

  

    If you transfer some imagery to a mosaic data is it sensible to expect a performance upgrade  (less crashes,    availability issues from remote sites)?

   Is that to broad of a question to get specific answer on?

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3 Replies
JayJohnsonWashoeCounty
Occasional Contributor III

One obvious advantage of publishing an image service directly from a #mosaic datset (assuming you have Image extension) is that you can add data to the mosaic and see the results immediately reflected in your service.  The alternative, creating an image cache, is time intensive and can consume really significant disk space, depending on your caching levels.

Jay
Washoe County GIS
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GuenterDoerffel
Esri Contributor

Hey Robert,

publishing a cache vs. a dynamic image service from a MosaicDataset is a very good and valid question. Here a few thoughts/facts:

CACHE:

Pre-generated, tiled dataset, limited to 8bit depth of data. Usually for visualization purposes only. Pre-defined scales. 

  • Advantages
    • Low (to nearly No) CPU load when using
    • (Potentially high) Pre-processing Load done just once when cached
    • Fast delivery/display optimized
  • Disadvantages
    • No suitable for data delivery other than 3band / 8 bit
      (Elevation, Multiband-Sat, 4-band Aerial)
    • Access to single org. images and their metadata is not available (since tiled)
    • Pre-Resampled to Cache scales
      (Any request inbetween cache scales will again resample)
    • Cache management needed for every data update (see Jays argument)
    • Not able to apply dynamic raster functions
      (Example: You have 4-band Aerials and want to provide Infrared, RGB, NDVI as views:
      Thats 3 caches ... but only ONE dynamic ImageService with 3 Functions for different views)


MOSAIC DATASET as IMAGE SERVICE: 
Dynamic (see additional comment (*) below!) access to imagery collection applying on-the-fly processing template(s). Any sale, selection, rule can be defined.

  • Advantages
    • For any type of raster data (bands, bit depth, ...)
    • Each request will have best possible quality as resampled only once for the scale asked for
    • Dynamic query of images creating the 'view' asked for (time, bands, attrib. query, mosaic method, order, ...) in the "format" (compression, bit depth, ...) asked for
    • Apply dynamic function chains (with parameters) on item, group, Mosaic level
      (so for example publish elevation data (i,e, from LIDAR) with templates for slope, elevation, hillshade, contours, ...)
    • Be very reactive on data compilation (added, removed, updated data in Mosaic, changed functions)
    • Full access to Imagery metadata for display/query
  • Disadvantages
    • Processing applied for every query CAN be computationally expensive
      (thats excatly why the discussion 'live-or-cache" exists)
    • Every server contact will go back to source data (*) and generate new image, whih will put load on the server (might be rather low, but nevertheless)

So it is all about what you need/want to offer and the trade-off between flexibility and 'un-burdening' the server to do CPU work.
(*) Please note: There is a combination of both: Mosaic Datasets can cache process chains results so that any query after the first one asking for a result is 'cheaper' ... and you can define a cache on the ImageService that will be used similar to a cache, whenever the ImageServer is called with default properties ... and only when settings for a query change (different output compression, attribute query, mosaic method, ...) a new Image will be generated.

Hope this helps. Feel free to ask for clarifications if this is not answering it.

Guenter

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Robert_CraigAshby1
New Contributor III

Thanks for the replies back on this. It sounds like mosaic data set have a great deal of advantages over other options.  I'll share those thoughts with colleague here. Another thing I am running into is the need to clip or remove a set of three banded rasters 255, 255, 255 values from the underlying raster. so they can be Mosaic together  That will be done thru either con statement to remove them or converting the SIDs to a file format that can iterated thru in List Rasters to clip them to a shapefile grid from existing script.  Probably I'll have to explore the options of the mosaic tab as well.

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