[Qgis-developer] raster visualization

Agustin Lobo alobolistas at gmail.com
Mon Apr 23 04:05:00 EDT 2012


Andrea,

Depending on the number of cells, dealing with > 20 raster files
requires a totally different approach.
Even for visualization, this is clearly a different problem than the
common RGB or multi-spectral imagery.
We cannot deal with 13000 raster layers in the same way as we do with a dozen.

Have you tried rasterlite?

Agus

El día 22 de abril de 2012 21:37, aperi2007 <aperi2007 at gmail.com> escribió:
> Hi Agus ,
> thx for your informations.
>
>
>> Opening the raster layers very fast but getting a bad visualization
>> would not be a major
>> waste of time? This is what currently happens to me: the initial
>> display is always useless.
>>
>
> I understand your point of view, but i guess is not a need for every users.
> Same users can't wait the 4+ minutes need for the elaboration of a raster.
> Again because an user could open usually more than 20 rasters for every
> session, I guess this elaboration should be absolutely optional to avoid a
> really big lost of time.
>
>
>> If your raster layers have similar statistics and or you want to
>> display them with the same stretching so
>> that grey levels or colors are comparable (which is often my case
>> also, with time series of ndvi for example), a common style file would
>> be the best solution.
>
> Your solution seem good to me.
>
> We have more set of rasters of ortophoto type colors and grey.
> Eachset of colors photo is surely with comparable levels, instead I don't
> know for the gray photo sets.
> They are too older (1954 and so on).
>
> Instead for raster cell (grid data) from Lidar:
> Just now we begin to merge all our sets to have a full land-cover.
> So we are merging 1x1, 2x2 and 3x3 meters cells.
> I don't know if this could have some trouble with having a comparable set of
> values, but guess of no.
>
> Surely is not possible to find a unique style good for all the sets, but is
> possible to establish a good style for each set.
>
>>...Perhaps, in
>
>> case a raster style is present, the by default procedure and
>> calculations could be bypassed. Would this be a good solution
>> in your case?
>>
>
> You mean a file raster-style in the same folder of the raster set or of the
> catalog file ?
> I guess this could be a good compromise to help the use in situation like
> ours.
>
> Andrea.
>
> Il 22/04/2012 19:43, Agustin Lobo ha scritto:
>
>> Andrea,
>>
>> Opening the raster layers very fast but getting a bad visualization
>> would not be a major
>> waste of time? This is what currently happens to me: the initial
>> display is always useless.
>>
>> If your raster layers have similar statistics and or you want to
>> display them with the same stretching so
>> that grey levels or colors are comparable (which is often my case
>> also, with time series of ndvi for example), a common style file would
>> be the best solution. Perhaps, in
>> case a raster style is present, the by default procedure and
>> calculations could be bypassed. Would this be a good solution
>> in your case?
>>
>> Agus
>>
>> El día 20 de abril de 2012 15:10, Andrea Peri<aperi2007 at gmail.com>
>>  escribió:
>>>>
>>>> - on initial load of a raster, generate a quicklook that is the larger
>>>> of 1/4 screen resolution or 500x500 pixels by sampling every nth pixel
>>>> - generate a histogram from the quicklook
>>>> - calculate clipped 2% - 96% range min max for each band
>>>> - apply a histogram stretch based on the above
>>>> - the histogram could be used for generating the graph in raster
>>>> props, and the quicklook could be used to create thumbs and previews
>>>> etc
>>>> - ideally we should cache these quicklooks and only regenerate them if
>>>> the underlying dataset has changed
>>>>
>>>> I believe if we do this we will have fast initial load and the images
>>>> (grayscale and rgb) will 'look right' when first loaded (i.e with good
>>>> contrast) and it would not be necessary to assign any color value to
>>>> grayscales by default.
>>>>
>>>> Regards
>>>
>>>
>>> Hi,
>>> just my 2 ct.
>>>
>>> I guess the more important capability with raster is to open they faster
>>> possible.
>>>
>>> I fear calculate all these values on first opened take more time than
>>> what
>>> is waitable for the open of a raster.
>>>
>>> Perhaps this action should be choosable by settings ?
>>>
>>> Of course I see our situation.
>>>
>>> Our situation is of more sets of raster (7-800 each set) where every
>>> raster
>>> is grey level or true color of 3-400 Mbyte each.
>>> And all these raster are accessible by a remote shared server to our
>>> users.
>>> For a total, actually, of about 13.000 rasters.
>>>
>>> I don't understand if this new feature could be really usable in a
>>> situation
>>> like our.
>>>
>>> --
>>> -----------------
>>> Andrea Peri
>>> . . . . . . . . .
>>> qwerty àèìòù
>>> -----------------
>>>
>>>
>>> _______________________________________________
>>> Qgis-developer mailing list
>>> Qgis-developer at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>>>
>>
>


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