Re: [gdal-dev] RFC 32 - gdallocationinfo utility

[Eli Adam]

Frank,

 This is a helpful new utility.  

I read the documentation and tried it out.  Using gdallocationinfo to find the 
elevation at a given lat/long location seems like a reasonable use.  It may be 
desirable to input and output an ogr layer rather than a single point.  For 
instance, what are the elevations at these points in this shapefile?  

I tried to approach that problem by putting the coordinates into a file with 
ogrinfo and then use that file as an --optfile for the x y.  That didn't work 
the way that I tried it.  Can an --optfile be used for the x y input?  

ogrinfo town.shp town | grep 'POINT' | sed 's/  POINT (//' | sed 's/)//'  
xyinput2.txt

head xyinput2.txt 
7350538.701077490113676 371057.403368594241329
7388905.153187953867018 357147.769300847954582
7346377.449287764728069 409114.138115067325998

gdallocationinfo -s_srs EPSG:2913 townraster.tif --optfile xyinput2.txt 
Usage: gdallocationinfo [--help-general] [-xml] [-lifonly] [-valonly]
[-b band]* [-s_srs srs_def] [-geoloc] [-wgs84]
srcfile x y

What would be the proper approach to the above hypothetical problem?  Is there 
an effective way to have an ogr input for gdallocaitoninfo?  Perhaps 
-input_file_list my_liste.txt for the x y similar to gdalbuildvrt?

It looks like -s_srs applies to the x y input.  -s_srs sometimes, i.e. 
gdalwarp, applies to the srcfile.  

Is -wgs84 equivalent to -s_srs EPSG:4326?

These were my initial thoughts I hope that some of them may be helpful.

Thanks for the new utility, Eli


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Re: [gdal-dev] RFC 32 - gdallocationinfo utility

[Frank Warmerdam]

Eli Adam wrote:

Frank,

 This is a helpful new utility.  

I read the documentation and tried it out.  Using gdallocationinfo to find the elevation at a given lat/long location seems like a reasonable use.  It may be desirable to input and output an ogr layer rather than a single point.  For instance, what are the elevations at these points in this shapefile?  

I tried to approach that problem by putting the coordinates into a file with ogrinfo and then use that file as an --optfile for the x y.  That didn't work the way that I tried it.  Can an --optfile be used for the x y input?  


ogrinfo town.shp town | grep 'POINT' | sed 's/  POINT (//' | sed 's/)//'  
xyinput2.txt

head xyinput2.txt 
7350538.701077490113676 371057.403368594241329

7388905.153187953867018 357147.769300847954582
7346377.449287764728069 409114.138115067325998

gdallocationinfo -s_srs EPSG:2913 townraster.tif --optfile xyinput2.txt 
Usage: gdallocationinfo [--help-general] [-xml] [-lifonly] [-valonly]

[-b band]* [-s_srs srs_def] [-geoloc] [-wgs84]
srcfile x y

What would be the proper approach to the above hypothetical problem?  Is there 
an effective way to have an ogr input for gdallocaitoninfo?  Perhaps 
-input_file_list my_liste.txt for the x y similar to gdalbuildvrt?


Eli,

As currently implemented gdallocationinfo only accepts one location on
the commandline.  The --optfile expansion is presumably working but
you can't give more than one xy pair on the commandline.


It looks like -s_srs applies to the x y input.  -s_srs sometimes, i.e. gdalwarp, applies to the srcfile.  


I gather you are suggesting the parameter name is confusing?   It might
make sense for me to call it -l_srs (location srs).  I'll make that
change.


Is -wgs84 equivalent to -s_srs EPSG:4326?


Yes - it's just a shortcut for a common case.

Best regards,
--
---+--
I set the clouds in motion - turn up   | Frank Warmerdam, warmer...@pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush| Geospatial Programmer for Rent

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