[gdal-dev] Geotiff AREA_OR_POINT

[Joaquim Luis]

On 28-06-2010 23:21, Michael Sumner wrote:
>> Am I correct in interpreting this post to mean that the pixel-is-area and pixel-is-point tiffs>are read the exact same way by GDAL, with the only difference being in the value of the>AREA_OR_POINT metadata key? Should viewers then be looking for>the "AREA_OR_POINT" key in addition to the georeferencing information, and shift the>display to center the top-left pixel on (0,0) if it's set to Point?
>>      
> That's my understanding, it's just a metadata tag there for use if you
> need it. I would say that viewers should only modify their behaviour
> from Area if they have the distinction for centre point vs. cell based
> views.
>
> I've seen it used to set  centre-based TIN-like renderings, vs.
> cell-based image renderings - but there's nothing in the GDAL raster
> storage model that prevents you taking on either interpretation AFAIK,
> though the default is cell-based.
>    


> (There can be a problem interpreting more flexible array formats like
> NetCDF, that can store irregularly spaced coordinate vectors for, say,
> the centres of cells on the X axis - and there's rarely any metadata
> (in the file) to say explicitly that it's centre- not corner-based.  )
>
> Cheers, Mike.
>    


netCDF grids created by GMT have always (~20 years) made that 
distinction and store that information.

Joaquim