[Geoserver-users] image mosaic pyramid with time dimension

GeoServer GeoServer User
1

In the near(ish) future I’m going to need to serve a set of aerial images that are periodically updated a tile at a time. In general users will want to see the latest images across the view (but will need to switch to the view that would have been seen on a particular day).

I’m thinking that I will need a database to store the index (and may be the images) but it’s not clear from the examples I can find if the ability to add tiles on an ad hoc basis is supported.

I’m also not clear on if I need to (or can) build a pyramid/mosaic or if I just mosaic the high res imagery and rely on the overviews to provide pyramid like qualities at lower zoom levels.

Has anyone done something similar and would you be prepared to share your experiences?

cheers

Ian

–
Ian Turton

2

Ciao Ian,
please, find my answer inline below...

Regards,
Simone Giannecchini

Our support, Your Success! Visit http://opensdi.geo-solutions.it for
more information.

Ing. Simone Giannecchini
@simogeo
Founder/Director

GeoSolutions S.A.S.
Via Poggio alle Viti 1187
55054 Massarosa (LU)
Italy
phone: +39 0584 962313
fax: +39 0584 1660272
mob: +39 333 8128928

http://www.geo-solutions.it
http://twitter.com/geosolutions_it

-------------------------------------------------------

On Tue, Aug 20, 2013 at 11:07 AM, Ian Turton <ijturton@anonymised.com> wrote:

In the near(ish) future I'm going to need to serve a set of aerial images
that are periodically updated a tile at a time. In general users will want
to see the latest images across the view (but will need to switch to the
view that would have been seen on a particular day).

I'm thinking that I will need a database to store the index (and may be the
images) but it's not clear from the examples I can find if the ability to
add tiles on an ad hoc basis is supported.

There has been a decent amount of work to add this functionality for
GeoServer 2.4.x which gives the possibility to
manipulate at runtime the index adding/removing tiles from the mosaic.

For previous versions of GeoServer you'd have to resort to add/remove
tiles directly from the underlying storage (e.g. DBMS).

I'm also not clear on if I need to (or can) build a pyramid/mosaic or if I
just mosaic the high res imagery and rely on the overviews to provide
pyramid like qualities at lower zoom levels.

It depends on the # of images you'll have in your mosaic and on the
scale you'll make them available.
If you are limiting yourself to work at small scales which means you
never load more than a few tiles then the ImageMosaic with embedded
overviews would do the job.

If you want to show the images at all scales and at large scales the #
of images to load in the view gets big (>> 50/60) then you are in
trouble, ImageMosaic would have to load too much stuff to work at
decent speed and in some cases you might simply kill your server with
the dreaded "too many files open" error.

Now, there are a number of things you can before resorting to use
ImagePyramid, but this mainly involves fiddling with merging tiles
into larger files to reduce their #.

If in the end the only way to go is the ImagPyramid, you need to
remember that it is just a bunch of ImageMosaic at different
resolutions, hence with the latest GeoServer you can resort to manage
the indipendently (yeah, things are more difficult with updates).
Right now the ImagePyramid does not exposes all the params of the
ImageMosaic for reading, but that would be a trivial change.

Has anyone done something similar and would you be prepared to share your
experiences?

I have been too coincise I know, but I am swamped and just hoping to
get the discussion going :slight_smile:

cheers

Ian

--
Ian Turton

------------------------------------------------------------------------------
Introducing Performance Central, a new site from SourceForge and
AppDynamics. Performance Central is your source for news, insights,
analysis and resources for efficient Application Performance Management.
Visit us today!
http://pubads.g.doubleclick.net/gampad/clk?id=48897511&iu=/4140/ostg.clktrk
_______________________________________________
Geoserver-users mailing list
Geoserver-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/geoserver-users

3

Hi Simone,

I would like to pick up the topic again as I am working on the very same
issue at the moment.

As a reminder:
We have a bulk of aerial imagery with the requirement to access historical
data (i.e. updates are added to the index in regular intervals, but the
imagery from a certain point in time should still be accessible after having
applied an update). We are intending to serve this with a time-enabled image
mosaic, holding the index in a database table.

As you already mentioned the ImageMosaic only provides a reasonable
performance if you have no more than 50-60 tiles in a view at the same time.
Therefore I would create pyramids to achieve a similar performance on every
zoomlevel, which I achieve by downsampling the original tiles and mosaicing
them to new tiles on currently three levels (we cannot use gdal directly,
therefore I am doing this in FME).

I have a few open questions with regard to this:
- What is the recommended tile size in pixels to achieve a reasonable
balance between number of tiles and disk access?
- For integration into Geoserver I currently see the option to create an
image mosaic for each pyramid level, add scale dependent styles to each of
them and then add all of the layers to a layer group (original tile
imagemosaic and the three lower resolution overviews). Do you think this
would be a good approach?
- You're talking about creating a layer based on an ImagePyramid as well,
but I guess this would not read the time and add it to the index of the
underlying mosaics, will it?

Thank you very much in advance!
Cheers,
Max

--
View this message in context: http://osgeo-org.1560.x6.nabble.com/image-mosaic-pyramid-with-time-dimension-tp5073298p5140777.html
Sent from the GeoServer - User mailing list archive at Nabble.com.