[gdal-dev] OSGeo.OGR.Geometry: Union the mutiple geometries at a time

[MRRAJESH]

Developers,

We came to know that OSGeo.OGR.Geometry is having the *Union *method which
allows to the union of the two geometries (code snippet below). But this
allows us one by one. How to union the multiple geometries (say 1000
geometries) at a time? Any methods or libraries in GDAL?

OSGeo.OGR.Geometry g1 = OSGeo.OGR.Geometry.CreateFromWkt("POLYGON(..
OSGeo.OGR.Geometry g2 = OSGeo.OGR.Geometry.CreateFromWkt("POLYGON(..
OSGeo.OGR.Geometry g3 = OSGeo.OGR.Geometry.CreateFromWkt("POLYGON(..

OSGeo.OGR.Geometry unionGeometry = (g1.Union(g2)).Union(g3);

Regards,
Rajesh



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Re: [gdal-dev] What is lost when converting 12 bit imagery to 8 bit?

[Frank Warmerdam]

Patrick,

FWIW, Rob's post is on the process he uses in Photoshop to prepare images
for various venues.  For imagery published through the platform we (Planet)
do not use per-image white-point and black-point (or we would not have day
to day, and scene to scene consistency).  We do apply color curves Rob
prepared in our automated process but with "fixed" black/white point which
results in an automated 8bit RGB product that tends to be very suboptimal
in dark or bright areas. The imagery Planet shows in our web-explorer
interface is served from highly compressed JPEG-in-TIFF adding an
additional layer of image damage. :-)  While that pains me, we are keeping
around nearly 3 billion scenes online at nearly full resolution for fast
visualization so some compromises have to be made.

Beyond nit-picking, I think my point is:
 - given 12bit "rawer" data you have the opportunity to do careful scene
dependent conversion to 8bit in a way that best brings out the details
available in the source data if you have the time and patience.
 - having this process done for you in advance by a skilled supplier
(perhaps in such a way as to maintain reasonable consistency for large area
coverages) may actually save you a lot of work if you mostly just want to
fairly generic visualization - and it might even be a better visualization
than you would do yourself if you aren't going to do a lot of work.

Best regards,
Frank

On Wed, Mar 17, 2021 at 11:13 PM Patrick Young <
patrick.mckendree.yo...@gmail.com> wrote:

> I would guess you usually see 8bit RGB images because that is what your
> monitor can display.   What is lost is a deeper question, per channel you
> have to squeeze the original [0 - 4095] pixel value range per channel down
> to [0 -255], and there are lots of ways to do it.  The problem is sometimes
> called tone mapping
> .
> Planet had a nice blog post describing how they manually convert their
> imagery to 8bit RGB here .
> If you were using the imagery for analytic things (e.g. converting pixel
> values to reflectance) you'd probably not want the 8bit product.
>
> To get GDAL in the mix, note that gdal_translate can do simple tone
> mapping for you:
> https://gdal.org/programs/gdal_translate.html#cmdoption-gdal_translate-scale
>
> Patrick
>
>
>
>
>
> On Wed, Mar 17, 2021 at 3:23 PM  wrote:
>
>> SPOT 6/7 satellite imagery is captured with a dynamic range of 12 bits
>> per pixel per channel (ref ). However
>> almost all of the SPOT imagery I have seen in use has been 8 bits per
>> channel, and split into RGB natural colour (Bands-321) and Near-infrared-RG
>> false colour (Bands-432). What information is lost in this 12 to 8 bits
>> conversion?
>>
>> I'm wondering if we should be altering our request for purchase
>> specifications to deliver the full bit depth.
>>
>> *Although I'm referencing SPOT imagery specifically the question is
>> general and really applies to any satellite or sensor system.*
>>
>> Cross-post:
>> https://gis.stackexchange.com/questions/390315/what-is-lost-when-converting-12-bit-imagery-to-8-bit
>>
>>
>>
>>
>>
>> *Matt Wilkie*
>>
>> Geomatics Analyst
>>
>> Environment | Technology, Innovation and Mapping
>>
>> T 867-667-8133 | *Yukon.ca *
>>
>> *Hours: 08:30-16:30, Tue-Wed: Office, Thu-Fri: Remote.*
>>
>>
>> ___
>> gdal-dev mailing list
>> gdal-dev@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/gdal-dev
>>
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> gdal-dev mailing list
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Re: [gdal-dev] What is lost when converting 12 bit imagery to 8 bit?

[Patrick Young]

I would guess you usually see 8bit RGB images because that is what your
monitor can display.   What is lost is a deeper question, per channel you
have to squeeze the original [0 - 4095] pixel value range per channel down
to [0 -255], and there are lots of ways to do it.  The problem is sometimes
called tone mapping
.
Planet had a nice blog post describing how they manually convert their
imagery to 8bit RGB here .
If you were using the imagery for analytic things (e.g. converting pixel
values to reflectance) you'd probably not want the 8bit product.

To get GDAL in the mix, note that gdal_translate can do simple tone mapping
for you:
https://gdal.org/programs/gdal_translate.html#cmdoption-gdal_translate-scale

Patrick





On Wed, Mar 17, 2021 at 3:23 PM  wrote:

> SPOT 6/7 satellite imagery is captured with a dynamic range of 12 bits per
> pixel per channel (ref ). However almost
> all of the SPOT imagery I have seen in use has been 8 bits per channel, and
> split into RGB natural colour (Bands-321) and Near-infrared-RG false colour
> (Bands-432). What information is lost in this 12 to 8 bits conversion?
>
> I'm wondering if we should be altering our request for purchase
> specifications to deliver the full bit depth.
>
> *Although I'm referencing SPOT imagery specifically the question is
> general and really applies to any satellite or sensor system.*
>
> Cross-post:
> https://gis.stackexchange.com/questions/390315/what-is-lost-when-converting-12-bit-imagery-to-8-bit
>
>
>
>
>
> *Matt Wilkie*
>
> Geomatics Analyst
>
> Environment | Technology, Innovation and Mapping
>
> T 867-667-8133 | *Yukon.ca *
>
> *Hours: 08:30-16:30, Tue-Wed: Office, Thu-Fri: Remote.*
>
>
> ___
> gdal-dev mailing list
> gdal-dev@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev
>
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[gdal-dev] What is lost when converting 12 bit imagery to 8 bit?

[Matt.Wilkie]

SPOT 6/7 satellite imagery is captured with a dynamic range of 12 bits per 
pixel per channel (ref). However almost all of 
the SPOT imagery I have seen in use has been 8 bits per channel, and split into 
RGB natural colour (Bands-321) and Near-infrared-RG false colour (Bands-432). 
What information is lost in this 12 to 8 bits conversion?

I'm wondering if we should be altering our request for purchase specifications 
to deliver the full bit depth.

Although I'm referencing SPOT imagery specifically the question is general and 
really applies to any satellite or sensor system.
Cross-post: 
https://gis.stackexchange.com/questions/390315/what-is-lost-when-converting-12-bit-imagery-to-8-bit


Matt Wilkie
Geomatics Analyst
Environment | Technology, Innovation and Mapping
T 867-667-8133 | Yukon.ca
Hours: 08:30-16:30, Tue-Wed: Office, Thu-Fri: Remote.

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