[Liblas-devel] Re: GetProj4() string and NAD83

[Frank Warmerdam]

On Tue, Jan 10, 2012 at 9:01 AM, Howard Butler <hobu.inc at gmail.com> wrote:
>
> On Jan 10, 2012, at 10:30 AM, Howard Butler wrote:
>> I'll try to dig into this some more...
>
> GDAL isn't turning this into a proper proj.4 string.
>
>>      GTModelTypeGeoKey (Short,1): ModelTypeProjected
>>       GTCitationGeoKey (Ascii,14): "UTM zone 15N"
>>       GeogGeodeticDatumGeoKey (Short,1): Datum_North_American_Datum_1983
>>       GeogEllipsoidGeoKey (Short,1): Ellipse_GRS_1980
>>       ProjectedCSTypeGeoKey (Short,1): PCS_NAD83_UTM_zone_15N
>>       ProjCoordTransGeoKey (Short,1): CT_TransverseMercator
>>       ProjLinearUnitsGeoKey (Short,1): Linear_Meter
>>       VerticalCSTypeGeoKey (Short,1): VertCS_North_American_Vertical_Datum_1988
>>       VerticalCitationGeoKey (Ascii,19): "GEOID 2003 Applied"
>>       VerticalUnitsGeoKey (Short,1): Linear_Meter
>
> is coming out of GDAL as:
>
>> +proj=tmerc +lat_0=0 +lon_0=0 +k=1 +x_0=0 +y_0=0 +datum=NAD83 +units=m +geoidgrids=g2003conus.gtx,g2003alaska.gtx,g2003h01.gtx,g2003p01.gtx +vunits=m +no_defs

Folks,

The problem is that ProjCoordTransGeoKey is seto to CT_TransverseMercator
but there are no actual projection method parameters.  When the Geokey
interpreter sees  ProjCoordTransGeoKey it looks for a user defined projected
coordinate system and ignores the predefined one (PCS_NAD83_UTM_zone_15N).

I consider this an improperly defined set of geokeys.  If ProjCoordTransGeoKey
is provided then the projection method parameters should also be provided.
Alternatively drop the ProjCoordTransGeoKey and let the system use
the ProjectedCSTypeGeoKey.

Best regards,
-- 
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