[gdal-dev] RE: progressive rendering

Norman Barker nbarker at ittvis.com
Mon Aug 18 20:06:32 EDT 2008


Thanks for the input, much appreciated since I would like to get this
interface defined.

A streaming driver so JPIPKAK for example would need to register as its
own driver to handle urls of the type jpip://, similarly ecwp would need
its own driver if it were to use the same callback for streaming data.
As such the management of GDALDataset::RasterIO and Band.RasterIO would
be the implementors responsibility, most likely this could be defined
with references back to the parent dataset as the controller thread.

The comment about raster x and y size is interesting, in the case of
jpip raster x and y size is known as a result of the image metadata
being transferred to the client in the initial request and can be
handled as overviews, for other formats like MrSID, ECW then I defer to
the better informed.

JPIP does have a client cache, and this data is needed between requests,
but I believe we can keep this data internal to the format driver.

Would it be possible to add this callback function as a stub method?



-----Original Message-----
From: Tamas Szekeres [mailto:szekerest at gmail.com] 
Sent: Monday, August 18, 2008 4:03 PM
To: Norman Barker
Cc: gdal-dev at lists.osgeo.org
Subject: Re: [gdal-dev] RE: progressive rendering


It seems like adding a GDALProgressFunc like parameter to RasterIO
would be a solution but I'm not totally sure about the negaive effects
of this change since these functions are frequently used.

Most of the drivers are doing band based rasterIO so you should also
deal with Band.RasterIO in addition. The default implementation of
GDALDataset::IRasterIO is calling the band based rasterIO functions of
the drivers. In such cases how the progress func. of the band based
raserIO would be bound to the progress func of the outer dataset?

I would also be curious to know how the underlying intermediary data
should be stored and would vary between the subsequent progress
reports. For example would the raster X and Y size be different or
would it be handed as a temporary buffers and datasets or bands (like
overviews) for example?

Best regards,


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