Re: [gdal-dev] Tag for units in GeoTIFF

2023-10-26 Thread Even Rouault via gdal-dev 


Le 26/10/2023 à 18:50, David Shean a écrit :

Hi Even and Javier,
For the special case of a DEM, would it make more sense to specify the 
units with a vertical CRS?  This approach would define the LENGTHUNIT 
and the associated vertical datum.


Example for EPSG:4979:

        AXIS["ellipsoidal height (h)",up,
            ORDER[3],
            LENGTHUNIT["metre",1]],

Example for EPSG:5703:

VERTCRS["NAVD88 height",
    VDATUM["North American Vertical Datum 1988"],
    CS[vertical,1],
        AXIS["gravity-related height (H)",up,
            LENGTHUNIT["metre",1]],
...

More complicated than specifying the generic UNITTYPE in raster 
metadata, but seems like best practice.


This is actually already implemented (deducing the value of 
GetUnitType() from the vertical component):


$ gdal_translate byte.tif out.tif -a_srs EPSG:4269+5703
$ gdalinfo out.tif | grep Unit
  Unit Type: foot

$ gdal_translate byte.tif out.tif -a_srs EPSG:4269+8228
$ gdalinfo out.tif | grep Unit
   Unit Type: foot



-David


On Oct 26, 2023, at 4:45 AM, Javier Jimenez Shaw via gdal-dev 
 wrote:


Thanks!

On Thu, 26 Oct 2023 at 12:27, Even Rouault via gdal-dev 
 wrote:


Javier,

Le 26/10/2023 à 11:59, Javier Jimenez Shaw via gdal-dev a écrit :

Hi

Using a GeoTIFF with a single band and float values can be very
useful to show any distribution over the terrain. One typical
example is DSM (digital surface model), where the value is the
elevation on every point.

Is there any standard (or accepted) metadata to say the units of
those values?


API wise in GDAL, you should use the
GDALRasterBand::SetUnitType() to set the unit

For TIFF, this will be encoded in the GDAL_METADATA TIFF tag like
the following:


  foo


Regarding the value itself, it is mostly unspecified by GDAL. It
could be a good practice to suggest to use strings recognized by
the "udunits" package (when possible), like done in the netCDF CF
conventions

(http://cfconventions.org/Data/cf-conventions/cf-conventions-1.10/cf-conventions.html#units)

Even



In the typical case of DSM it is usually "meter" or "foot". But
it can be something else, like "people/km2" for population, or
"mm" for rain precipitation, or "kg/ha" for agricultural yield.

Thanks
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Re: [gdal-dev] Tag for units in GeoTIFF

2023-10-26 Thread David Shean via gdal-dev 
Hi Even and Javier,
For the special case of a DEM, would it make more sense to specify the units 
with a vertical CRS?  This approach would define the LENGTHUNIT and the 
associated vertical datum.

Example for EPSG:4979:

AXIS["ellipsoidal height (h)",up,
ORDER[3],
LENGTHUNIT["metre",1]],

Example for EPSG:5703:

VERTCRS["NAVD88 height",
VDATUM["North American Vertical Datum 1988"],
CS[vertical,1],
AXIS["gravity-related height (H)",up,
LENGTHUNIT["metre",1]],
...

More complicated than specifying the generic UNITTYPE in raster metadata, but 
seems like best practice.
-David


> On Oct 26, 2023, at 4:45 AM, Javier Jimenez Shaw via gdal-dev 
>  wrote:
> 
> Thanks!
> 
> On Thu, 26 Oct 2023 at 12:27, Even Rouault via gdal-dev 
> mailto:gdal-dev@lists.osgeo.org>> wrote:
> Javier,
> 
> Le 26/10/2023 à 11:59, Javier Jimenez Shaw via gdal-dev a écrit :
>> Hi
>> 
>> Using a GeoTIFF with a single band and float values can be very useful to 
>> show any distribution over the terrain. One typical example is DSM (digital 
>> surface model), where the value is the elevation on every point.
>> 
>> Is there any standard (or accepted) metadata to say the units of those 
>> values?
> API wise in GDAL, you should use the GDALRasterBand::SetUnitType() to set the 
> unit
> 
> For TIFF, this will be encoded in the GDAL_METADATA TIFF tag like the 
> following:
> 
> 
>   foo
> 
> 
> Regarding the value itself, it is mostly unspecified by GDAL. It could be a 
> good practice to suggest to use strings recognized by the "udunits" package 
> (when possible), like done in the netCDF CF conventions 
> (http://cfconventions.org/Data/cf-conventions/cf-conventions-1.10/cf-conventions.html#units
>  
> )
> 
> Even
> 
>> 
>> In the typical case of DSM it is usually "meter" or "foot". But it can be 
>> something else, like "people/km2" for population, or "mm" for rain 
>> precipitation, or "kg/ha" for agricultural yield.
>> 
>> Thanks
>> .___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ...  ._ .__
>> 
>> 
>> ___
>> gdal-dev mailing list
>> gdal-dev@lists.osgeo.org 
>> https://lists.osgeo.org/mailman/listinfo/gdal-dev 
>> 
> -- 
> http://www.spatialys.com 
> My software is free, but my time generally not.
> ___
> gdal-dev mailing list
> gdal-dev@lists.osgeo.org 
> https://lists.osgeo.org/mailman/listinfo/gdal-dev 
> 
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Re: [gdal-dev] Tag for units in GeoTIFF

2023-10-26 Thread Javier Jimenez Shaw via gdal-dev 
Thanks!

On Thu, 26 Oct 2023 at 12:27, Even Rouault via gdal-dev <
gdal-dev@lists.osgeo.org> wrote:

> Javier,
> Le 26/10/2023 à 11:59, Javier Jimenez Shaw via gdal-dev a écrit :
>
> Hi
>
> Using a GeoTIFF with a single band and float values can be very useful to
> show any distribution over the terrain. One typical example is DSM (digital
> surface model), where the value is the elevation on every point.
>
> Is there any standard (or accepted) metadata to say the units of those
> values?
>
> API wise in GDAL, you should use the GDALRasterBand::SetUnitType() to set
> the unit
>
> For TIFF, this will be encoded in the GDAL_METADATA TIFF tag like the
> following:
>
> 
>   foo
> 
>
> Regarding the value itself, it is mostly unspecified by GDAL. It could be
> a good practice to suggest to use strings recognized by the "udunits"
> package (when possible), like done in the netCDF CF conventions (
> http://cfconventions.org/Data/cf-conventions/cf-conventions-1.10/cf-conventions.html#units
> )
>
> Even
>
>
> In the typical case of DSM it is usually "meter" or "foot". But it can be
> something else, like "people/km2" for population, or "mm" for rain
> precipitation, or "kg/ha" for agricultural yield.
>
> Thanks
> .___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ...  ._ .__
>
> ___
> gdal-dev mailing 
> listgdal-dev@lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/gdal-dev
>
> -- http://www.spatialys.com
> My software is free, but my time generally not.
>
> ___
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> gdal-dev@lists.osgeo.org
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>
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Re: [gdal-dev] Tag for units in GeoTIFF

2023-10-26 Thread Even Rouault via gdal-dev 

Javier,

Le 26/10/2023 à 11:59, Javier Jimenez Shaw via gdal-dev a écrit :

Hi

Using a GeoTIFF with a single band and float values can be very useful 
to show any distribution over the terrain. One typical example is DSM 
(digital surface model), where the value is the elevation on every point.


Is there any standard (or accepted) metadata to say the units of those 
values?


API wise in GDAL, you should use the GDALRasterBand::SetUnitType() to 
set the unit


For TIFF, this will be encoded in the GDAL_METADATA TIFF tag like the 
following:



  foo


Regarding the value itself, it is mostly unspecified by GDAL. It could 
be a good practice to suggest to use strings recognized by the "udunits" 
package (when possible), like done in the netCDF CF conventions 
(http://cfconventions.org/Data/cf-conventions/cf-conventions-1.10/cf-conventions.html#units)


Even



In the typical case of DSM it is usually "meter" or "foot". But it can 
be something else, like "people/km2" for population, or "mm" for rain 
precipitation, or "kg/ha" for agricultural yield.


Thanks
.___ ._ ..._ .. . ._.  .___ .. __ . _. . __..  ...  ._ .__

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My software is free, but my time generally not.
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