Re: [gdal-dev] Histograms without null pixels

[Caleb Hanger]

On Tue, Mar 05, 2013 at 11:19:27AM +0530, Chaitanya kumar CH wrote:

> Caleb,
> 
> gdalinfo uses the GetDefaultHistogram() method which can do this faster by
> fetching a precomputed histogram.

What do you mean?  The histogram is only precomputed if gdalinfo has been run 
previously and stored a cache of data (the XML file) for later reference; 
please correct me if I'm wrong.  Otherwise, it seems to me that the data *must* 
be analyzed and the data computed; there is no way around that.  Additionally, 
I don't think it makes sense to say that it is faster to assemble a histogram 
that includes out-of-range values than to assemble a histogram that does not, 
because the latter is a subset contained within the former.

> gdalinfo is a command line program. Even a default histogram of 256 buckets
> is hard to visualize in text mode. A much better way is to use a desktop
> GIS like qgis to view the histogram.

A desktop GIS is not practical for providing a shell script meant to automate a 
repetitive (and much larger) task, with a small chunk of data that it needs for 
a single step in the process.  That is, I don't need to "visualize" the data -- 
I just need to get the information.  The more primitive the format, the better, 
as I like things that are lean and mean, and I know how to instruct the script 
to do the required mathematics upon the text-only histogram.

> Can you justify adding this extra functionality in gdalinfo?

Yes: quite simply, a histogram that does not include illegitimate values makes 
more sense than a histogram that does include them.  At least, this is the case 
in my experience; perhaps there are situations I'm unfamiliar with in which the 
histogram is desired to include values outside of the histogram's range, for 
some reason.  I'd even go so far as to say that gdalinfo currently *lies* about 
the histogram, telling the user that the histogram shows "256 buckets from X to 
Y" even though the histogram includes values which are *outside of that range*.

Arguably an even better justification is that the machinery to exclude the 
illegitimate values is already present in GetHistogram, so *very* few lines of 
code would need to be added to gdalinfo, simply to provide a flag for the user 
and if that flag is specified, pass "false" for the right parameter to 
GetHistogram (bIncludeOutOfRange), instead of just calling GetDefaultHistogram.

> On Tue, Mar 5, 2013 at 10:56 AM, Caleb Hanger  wrote:
> 
> > All,
> >
> > I am writing a script which is calling gdalinfo to get a histogram of
> > pixel values in an image file.  Apparently the mechanism for obtaining a
> > "default" histogram enables the "bIncludeOutOfRange" flag to dump
> > not-in-range pixels (including null pixels, in formats that support it)
> > into whichever bin of the histogram is closest.  I see that in the
> > GetHistogram() function, the functionality is already coded to respond
> > appropriately to either a true *or* false value in this flag.  However, I
> > can't seem to find any way to turn that flag off through any of the
> > user-level programs (in particular, gdalinfo), rendering the parameter to
> > the function useless, unless I'm just not looking hard enough.  Hence, my
> > questions:
> >
> > 1) Is there any standard user-level operation (preferably in gdalinfo)
> > which disables, or at least *allows* for disabling of, the
> > bIncludeOutOfRange flag?  If so, I can't find it.
> > 2) If not, how come?  Has there been no apparent need for histograms that
> > omit null values or other "out of range" situations?
> >
> > Thanks in advance for any insight,
> > Caleb Hanger
> > ___
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> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> >
> 
> 
> 
> -- 
> Best regards,
> Chaitanya kumar CH.
> 
> +91-9494447584
> 17.2416N 80.1426E
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Re: [gdal-dev] Histograms without null pixels

[Chaitanya kumar CH]

Caleb,

gdalinfo uses the GetDefaultHistogram() method which can do this faster by
fetching a precomputed histogram.
gdalinfo is a command line program. Even a default histogram of 256 buckets
is hard to visualize in text mode. A much better way is to use a desktop
GIS like qgis to view the histogram.

Can you justify adding this extra functionality in gdalinfo?



On Tue, Mar 5, 2013 at 10:56 AM, Caleb Hanger  wrote:

> All,
>
> I am writing a script which is calling gdalinfo to get a histogram of
> pixel values in an image file.  Apparently the mechanism for obtaining a
> "default" histogram enables the "bIncludeOutOfRange" flag to dump
> not-in-range pixels (including null pixels, in formats that support it)
> into whichever bin of the histogram is closest.  I see that in the
> GetHistogram() function, the functionality is already coded to respond
> appropriately to either a true *or* false value in this flag.  However, I
> can't seem to find any way to turn that flag off through any of the
> user-level programs (in particular, gdalinfo), rendering the parameter to
> the function useless, unless I'm just not looking hard enough.  Hence, my
> questions:
>
> 1) Is there any standard user-level operation (preferably in gdalinfo)
> which disables, or at least *allows* for disabling of, the
> bIncludeOutOfRange flag?  If so, I can't find it.
> 2) If not, how come?  Has there been no apparent need for histograms that
> omit null values or other "out of range" situations?
>
> Thanks in advance for any insight,
> Caleb Hanger
> ___
> gdal-dev mailing list
> gdal-dev@lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>



-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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[gdal-dev] Histograms without null pixels

[Caleb Hanger]

All,

I am writing a script which is calling gdalinfo to get a histogram of pixel 
values in an image file.  Apparently the mechanism for obtaining a "default" 
histogram enables the "bIncludeOutOfRange" flag to dump not-in-range pixels 
(including null pixels, in formats that support it) into whichever bin of the 
histogram is closest.  I see that in the GetHistogram() function, the 
functionality is already coded to respond appropriately to either a true *or* 
false value in this flag.  However, I can't seem to find any way to turn that 
flag off through any of the user-level programs (in particular, gdalinfo), 
rendering the parameter to the function useless, unless I'm just not looking 
hard enough.  Hence, my questions:

1) Is there any standard user-level operation (preferably in gdalinfo) which 
disables, or at least *allows* for disabling of, the bIncludeOutOfRange flag?  
If so, I can't find it.
2) If not, how come?  Has there been no apparent need for histograms that omit 
null values or other "out of range" situations?

Thanks in advance for any insight,
Caleb Hanger
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Re: [gdal-dev] Creation/read format question

[Chaitanya kumar CH]

Hi Tyler,

'ro' and 'rw' mean what they imply.

The '+' symbol tells that the format supports the Create() method. So, we
can use them to create a dataset from scratch and add metadata explicitly.
Without it, we need a 'template' dataset.

The 'v' means that the format driver supports the virtual system interface.
Note that there may be drivers that support it but don't report that they
do.


On Tue, Mar 5, 2013 at 9:01 AM, Tyler Mitchell wrote:

> Not sure how to describe it, but when gdal lists available formats, I see
> a few different ways that formats are marked as read, write, etc.
> The "rw" and "ro" items are easy enough for me to understand, but what
> about:
> "rov"
> "rw+v"
> "rwv"
> "rw+"
> ?
>
> Does the "v" refer to support in VRTs perhaps?
> Do  rw+v, rwv, rw+ all mean same thing?
>
> Any tips appreciated :)
>
> Tyler
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>



-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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[gdal-dev] Creation/read format question

[Tyler Mitchell]

Not sure how to describe it, but when gdal lists available formats, I see a few 
different ways that formats are marked as read, write, etc.
The "rw" and "ro" items are easy enough for me to understand, but what about:
"rov" 
"rw+v"
"rwv"
"rw+"
?

Does the "v" refer to support in VRTs perhaps?
Do  rw+v, rwv, rw+ all mean same thing?

Any tips appreciated :) 

Tyler
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[gdal-dev] How to identify custom lines in .Dgn file using DgnLib ?

[taibc]

Hi everyone,

I am getting a problem, I can't identify custom lines in .Dgn file.

As you know, in Microstation 7, we can assign the style value of lines from
0 to 7.

But if  lines are customed lines, they always have the style value is 0. How
can we identify them ?

Please find the attached image and dgn files for demo.

Thank you very much for your help !

 
SD.dgn   



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