[gdal-dev] GDAL Erdas LAN/GIS driver

[Roger Bivand]

On Fri, 21 Aug 2009, Roger Bivand wrote:

> On Fri, 21 Aug 2009, Frank Warmerdam wrote:
>
>> Roger Bivand wrote:
>>> Hi,
>>> 
>>> The code for the LAN/GIS driver uses GDT_Int16 for Pixel type 2, rather 
>>> than GDT_UInt16. Is this justified? A user of rgdal has a case of unsigned 
>>> 16-bit data stored by "a forest landscape model", being treated by the 
>>> driver as signed. The header does not seem to have a signed/unsigned flag. 
>>> Is this a problem of ambiguity in use of a (closed?) specification, or 
>>> should the driver be using GDT_UInt16?
>>> 
>>> I'm asking on the list first, because this may be ambiguity, not a bug.
>> 
>> Roger,
>> 
>> The only specification information I have on the format does not indicate
>> whether 16bit values should be treated as signed or unsigned.  If you are
>> confident that it should be treated as unsigned file a ticket and we will
>> fix it - hopefully this won't just break it for someone else!
>
> Frank,
>
> Thanks, I'm waiting to receive the affected file. I'll let you know when I've 
> got it.

(reverting to list)

Correction, the user reported that:

> Apparently, gdalinfo retrieves the correct min, max, and statistics, 
> despite the use of GDT_Int16.

on his Windows platform. The different GDAL versions ought to explain why 
his gdalinfo says Int16 but gives statistics from UInt16.

He has:

>From FWTools:
gdalinfo --version
GDAL 1.7.0dev, FWTools 2.4.2 released 2009/06/24

C:\Program Files\FWTools2.4.2>gdalinfo stand_bm.gis
Driver: LAN/Erdas .LAN/.GIS
Files: c:\landis\harvest_problem\FTT-N_MinT-N\stand_bm.gis
       c:\landis\harvest_problem\FTT-N_MinT-N\stand_bm.gsw
Size is 1758, 839
Coordinate System is:
LOCAL_CS["Unknown",
    UNIT["Meter",1]]
Origin = (33773.261718750000000,945478.062500000000000)
Pixel Size = (100.000000000000000,-100.000000000000000)
Corner Coordinates:
Upper Left  (   33773.262,  945478.063)
Lower Left  (   33773.262,  861578.063)
Upper Right (  209573.262,  945478.063)
Lower Right (  209573.262,  861578.063)
Center      (  121673.262,  903528.063)
Band 1 Block=1758x1 Type=Int16, ColorInterp=Undefined
  Min=0.000 Max=48499.000
  Minimum=0.000, Maximum=48499.000, Mean=12833.830, StdDev=13635.800
  Metadata:
    STATISTICS_MINIMUM=0
    STATISTICS_MAXIMUM=48499
    STATISTICS_MEAN=12833.830260712
    STATISTICS_MEDIAN=8.7254821994872e-239
    STATISTICS_MODE=3.9864100424366e-293
    STATISTICS_STDDEV=13635.800289332
    LAYER_TYPE=thematic


rgdal_0.6-12
> getGDALVersionInfo()
[1] "GDAL 1.6.1, released 2009/05/11"

For me on x86_64, GDALinfo() in rgdal and 1.6.2 gdalinfo -stats agree.

$ gdalinfo -stats stand_bm.gis
Driver: LAN/Erdas .LAN/.GIS
Files: stand_bm.gis
Size is 1758, 839
Coordinate System is:
LOCAL_CS["Unknown",
     UNIT["Meter",1]]
Origin = (33773.261718750000000,945478.062500000000000)
Pixel Size = (100.000000000000000,-100.000000000000000)
Corner Coordinates:
Upper Left  (   33773.262,  945478.062)
Lower Left  (   33773.262,  861578.062)
Upper Right (  209573.262,  945478.062)
Lower Right (  209573.262,  861578.062)
Center      (  121673.262,  903528.062)
Band 1 Block=1758x1 Type=Int16, ColorInterp=Undefined
   Minimum=-32140.000, Maximum=29620.000, Mean=8315.507, StdDev=13186.107
   Metadata:
     STATISTICS_MINIMUM=-32140
     STATISTICS_MAXIMUM=29620
     STATISTICS_MEAN=8315.5065072863
     STATISTICS_STDDEV=13186.10731815

On the trunk, GDT_Int16 is used too, so how does gdalinfo detect that it 
is actually UInt16?

Roger

>
> Best wishes,
>
> Roger
>
>> 
>> Best regards,
>> 
>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no