[Gvsig_english] Raster pyramids and INTEROPERABILITY

[virginia morales segura]

Hi Frank, Ernesto,

we appreciate so much all your suggestions, we  will transfer them to 
our  developpers.

Best regards.

Frank Warmerdam escribió:
> ernesto sferlazza wrote:
>   
>> Hello developers,
>> in the county government organization where I work we currently work
>> both with commercial (ESRI ArcGIS Desktop) and Open Source (gvSIG,
>> adbToolbox, the latter being a customization of OpenJump) GIS
>> software.
>> All raster layers in the geographic archive are stored together with
>> the pyramids, built by arcGIS, to optimize display rendering and
>> zooming with this software.
>> The problem is that when the a raster layer is loaded into a gvSIG
>> view,  the existence of pyramids causes problems in visualization
>> (e.g. for a B/W - 1 bit - image, zooming to the whole raster extent it
>> appears displayed all black, while zooming in, at a certain extent,
>> the image is displayed correctly).
>> The trick is to brutally delete the pyramid file  (*.rrd) associated
>> to the raster, but when we load tagain the raster on a ArcGIS View
>> Frame the image is displayed with a coarse resolution (compared with
>> the high quality resolution and zoom speed obtained with pyramids).
>> I suggest two alternative solution:
>> a) force gvSIG to ignore pyramids;
>> b) syncronize the behaviour of gvSIG with that of ArcGis regarding the
>> pyramids rendering.
>>     
>
> Ernesto,
>
> I'm willing to assist a bit on this problem.
>
> ArcGIS rrd's for 1 bit images use 8bit overviews so that greyscale
> values can be used to provide a smoother view to decimated line work.
>
> In GDAL I set the special RESAMPLING: AVERAGE_BIT2GRAYSCALE metadata
> on such overviews.  In GDALBandGetBestOverviewLevel(), used by the
> default GDAL RasterIO machinery, I avoid using such overviews for
> default decimation.
>
> So GDAL by default tries to avoid using these overviews automatically.
> But applications that fetch the list of overviews for bands, and use
> them directly may still end up utilizing these overviews.
>
> I must confess to not knowing gvSig's raster architecture well, but if it
> is reading .rrd's I'm guessing GDAL is being used.  In that case I suspect
> gvSig is directly reading the overviews.  It may be sufficient for gvSig
> to avoid overviews with the above metadata set, or alternatively to use
> a different display strategy for them, but to still utilize them (the
> optimal case).
>
> If gvSig is not using GDAL for this at all, then it still might want to
> implement a similar strategy.
>
> Best regards,
>