[mapserver-dev] fastpath 4326->3857 reprojections

[thomas bonfort]

I've just added this fastpath code (disabled by default, activated
with --enable-proj-fastpath) to a "proj" branch, along with some code
to use the thread-unlocked pj_tansform calls for proj 4.8. Unless
there's an objection, I'll merge it into master before we release 6.2.

best regards,
thomas

On Mon, Feb 13, 2012 at 14:51, Jeff McKenna
<jmckenna at gatewaygeomatics.com> wrote:
> I think the fast patch should work both ways (4326 to 3857, and 3857 to
> 4326).
>
> I'm a strong +1 on using the approved 3857 EPSG code only, and forcing those
> to upgrade their legacy use of 900913 (yes, as painful as that can be).
>
> -jeff
>
>
>
>>>>
>>>> On 2/11/2012 4:37 AM, thomas bonfort wrote:
>>>>>
>>>>>
>>>>> Hi all,
>>>>>
>>>>> During the codesprint I talked to Daniel about a possible speedup
>>>>> patch we could use to bypass going through proj when performing the
>>>>> common 4326 to 3857 (google mercator) reprojections. During my trip
>>>>> back from the codesprint I implemented a quick patch that does this,
>>>>> and I think that the benefits are sufficiently important under this
>>>>> (rather common) test case to merit being pushed to trunk.
>>>>>
>>>>> test-case:
>>>>> - using the mapserver-utils osm mapfile, we seed the first 6 zoom
>>>>> levels of the google-mercator grid. Depending on the zoom level, this
>>>>> mapfile has two (land and borders) or one (borders) layers that need
>>>>> to go through reprojection. There are between 1 and 4 other layers
>>>>> that are already in 3857 and therefore do not need reprojecting.
>>>>> - the seeding is done with the mapcache seeding tool, which can be
>>>>> configured to use multiple threads to do parallel rendering. The
>>>>> seeding is done by directly using the libmapserver api (i.e. direct
>>>>> calls to msDrawMap, not going through curl http getmap requests).
>>>>> - bug 4041 (http://trac.osgeo.org/mapserver/ticket/4041) contains a
>>>>> patch to avoid locking inside mapserver around proj calls, for trunk
>>>>> versions of proj. In the following result spreadsheet "with/without
>>>>> 480" refers to the fact that this patch is applied or not (480 stands
>>>>> for version 4.8.0 of proj)
>>>>>
>>>>> without further ado, here's the resulting spreadsheet, which gives the
>>>>> time in seconds needed to entirely seed the first 6 zoom levels:
>>>>>
>>>>>
>>>>>
>>>>> https://docs.google.com/spreadsheet/pub?key=0AnCiCdIXpTHidHJ0YzVmSW54WncwZ2lGSS1wQ2xNZHc&output=html
>>>>>
>>>>>
>>>>> tl;dr
>>>>>
>>>>> - if we factor out thread locking (which concerns the cgi/fastcgi
>>>>> performance), the speedup is x 2.5
>>>>> - in the multithreaded seeding case, the speedup is x 37
>>>>>
>>>>> --
>>>>> thomas
>
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