[Geomoose-users] caching aerial photos in MapServer

[TC Haddad]

Hi Tim,

I get the idea you are looking for the big picture of how caching can fit
into what you want to do. I agree with Dan that you should look into
MapCache.

Basically if you have MapCache set up in front of your MapServer, all
requests past first through MapCache, which first checks if the request
already exists in the cache, and if so, it shortcuts the process and never
needs to talk to MapServer, as it can serve the tile directly from the
cache. If an area has never been requested before, the request is
transferred to MapServer, which does it's thing, and passes it's result
back to MapCache for storage for future requests.  This model is a "cache
on demand" situation, which is different than "cache in advance", where you
might generate all the tiles possible in advance. Caching in advance is
also possible, but usually requires a larger amount of disk space to be
available than aching on demand does.

>From your MapServer map file perspective, Your map files are set up as you
normally would. MapCache is an Apache module that must be enabled in Apache
in order for you to use it. You configure it using a Configuration XML file
where you point it at the MapServer services that you would like to cache.

>From your front end user perspective, all that is different is the base URL
that you send them to for the cached services (MapCache base URL vs raw
MapServer URL). So usage for the user is totally the same as non-cache
usage. In my experience caching does improve performance, especially if
your user interface is making tiled requests, rather than single image WMS
requests.

A few other advantages of using MapCache:

- MapCache will allow requests of multiple tiling schemes from the same
cache - e.g. TMS, Google Maps, WMTS
- you can choose to cache an irregular subset of your imagery - for example
a watershed basin - and save on the disk space of all the pixels outside of
your basin

I'm sure there are more, but these are the ones that I have found most
handy.

Tanya



On Thu, Nov 3, 2016 at 8:58 AM, Eli Adam <eadam at co.lincoln.or.us> wrote:

> I've found that with well optimized tiffs (single YCBCR JPEG
> compressed tiff in the correct projection with overviews), there is
> essentially no time or processing spent accessing and producing aerial
> views.  What time is spent delivering imagery to the client is usually
> network transfer time which will be the same in cached and non-cached
> cases.
>
> The command line tool, shp2img, can be used to give timing information
> from your mapfile.
>
> Have you concluded that caching (i.e. file access and processing
> times) would indeed speed up your application?
>
> MapServer or GDAL lists might be better for aerial imagery
> optimization, serving, and caching discussions.  Searching the
> archives on nabble might turn up past discussions too.
>
> Best regards, Eli
>
> On Thu, Nov 3, 2016 at 8:18 AM, Dan Little <theduckylittle at gmail.com>
> wrote:
> > Have you looked at mapcache? http://mapserver.org/mapcache/
> >
> > Brought to you by the good folks at MapServer.
> >
> > On Thu, Nov 3, 2016 at 9:50 AM, Tim Hennig <timhbellevue at gmail.com>
> wrote:
> >> HI Everyone,
> >>
> >> I was wondering if someone can direct me to good information regarding
> >> caching aerial photos in MapServer.  I know this is not a GeoMoose
> question
> >> pertaining to the application, but I would like to start researching
> this
> >> and possibly implement this sometime in the next month.
> >>
> >> I’ve looked at the MapServer website, but I’m trying to figure out the
> >> process.  Can use ArcGIS cache tiles and tie it into MapServer?  Is
> there an
> >> add-on QGIS to cache? Etc.?
> >>
> >> I also thought about using REST services from the county that I reside
> in,
> >> but the caching is not as detailed at a municipal level.
> >>
> >> Right now the GeoMoose is using TIF images.
> >>
> >> Tim Hennig
> >> Village of Bellevue
> >>
> >>
> >>
> >>
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