View Full Version : One more time about Mercator
04-01-2010, 04:12 PM
I have a big tiled cache into mercator projection.
I want to try to display my cache using WWJ into intranet.
Can I do it without data reprojection? The cashe is too big and I does not have the time to reproject it.
Can WW WMS reproject data on the fly? As I can see it uses the GDAL library, which can reproject data from any projection.
Excuse me for my dilettantish questions, I am beginner at WWJ usage. :)
04-01-2010, 09:38 PM
Do a search in the SDK and this forum for "Mercator"
There are some examples in experimental\ ...... \Mercator
You will probably find that with your cache the CPU usage will be very high.
04-02-2010, 04:19 AM
Thanks a lot for response!
As I understand, all plugins which can reproject data are the client side applications.
Is it possible to reproject data on the fly on the server side? Could WMS (WW WMS or another, such as GeoServer) do it?
04-02-2010, 05:13 AM
Some of the terminology may be confusing. "plugins" were used in the .net version of WW. In the WWJ version many of the functions that are in the SDK can be used with a WWJ app but they are not what many think of as a "plugin" but a class that can be used.
A WMS has the ability to take a large image and make tiles on request. You have the data in a cache so the "make tiles on request" from a large image may not be applicable.
To reproject the data you have to the WWJ format like 512x512 on the fly may be taxing the CPU until your app may become unresponsive.
If your "cashe is too big ... to reproject" you may be better using that data with GoogleEarth, MS VE or wherever with those apps. To use that data in WWJ it has to be in a format that is compatible.
If there is another way I would like to know what that is also.
What was the origin of your cache, that may help?
If you have a separate server with it's own CPU/s that may be able to do the reprojection and leave your computers CPU to do it's thing without being overtaxed.
Also consider the java heap space for wherever the reprojection will be done.
edit: You question is OK but you might consider reprojecting "dilettantish" to something that is commonly used so a Google search is not required to find out what it means.
04-02-2010, 03:10 PM
Thank you for detailed answer.
Now I see that the full cache reprojection is not so bad idea.
I works in data receiving center, which has own receiving station.
Station works more than 5 years and we have the big data cache from some satellites, such as SPOT, IRS, LANDSAT and others. The cache size is 3 Tb approximately.
We have the own 2D visualization service into our intranet such as Google Maps and all cache was tiled into mercator projection for this service.
Now I must make 3D visualisation intranet service for our data at short time.
I don't see how Google Earth or MS VE can helps me in this task.
I think that WWJ is the best solution, but it uses the lat/lon projection.
As I can see I have two ways.
The first is reproject all cache into lat/lon, but I think that we will need one month for all data reprojection. In this case I will need support two caches in mercator proj. for 2D and lat/lon for 3D. It's no good.
The second way is reproject data on the fly. But as I understand from your reply it may works very slow.
Please give me the hint in this trouble as it possible.
WMS servers like Mapserver or Geoserver can reproject raster data on the fly. (I haven't used WW WMS so I don't know if it's possible there.) That's the whole idea - you got some data in one specific projection, but your WMS can serve images in many different systems. But WMS requires many resources and is quite slow. If you want fast access then you need tiles - this means you have to create a second lat/lon cache.
You said you have tiled data for Google Maps - do you still have the original files? Maybe it would be better to use them in WMS than those Mercator tiles.
04-03-2010, 02:41 PM
Yes, we keep the original data files into our archive. But the archiving level is not GeoTIFF. Our archive contains RAW data flow from satellites only. If I want to obtain lat/lon tiles from original data files I will must process all RAW data (level 0) to level 1B (radiometric and geometric corrected geolocated TIFF). The time for this procedure is no one month. :)
As I see from your comments data reprojection on the fly on the server side is very bad idea. But that you think about client side reprojection? Will it work fast?
As I understand the main problem of server side solution is many users which want to get reprojected tiles simultaneously. This problem does not exist in client side solution. But may be I don't see some "underwater stones"?
I wouldn't say that server-side reprojection is a bad idea - as long as you have a powerful machine and a relatively small number of users.
With client-side everything depends on users' computers - some may have new and fast PCs, some may have old laptops etc. (and remember that apart from reprojection they'd need to display 3d graphic which itself is resource hungry)
There is no easy answer, both ways have some pros and cons. Both require additional CPU power - the question is who's got more power to spare: server or users?
04-03-2010, 05:12 PM
Thank you very much!
You consultation was very helpful for me.
May be you can say something about this question (http://forum.worldwindcentral.com/showthread.php?t=24703)?
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