[gdal-dev] beginner or bug: reprojecting using ogr2ogr

[Alex Hagen-Zanker]

Dear all,

I just did my first reprojection using ogr2ogr. The process went quite 
patchy and I wonder if this is because of a bug or because I am not 
understanding something really basic.

I want to reproject a point dataset from British National Grid 
(EPSG:27700) to WGS84.

My input comes as comma separated values. Therefore I use GDAL 1.7 which 
offers great support for VRT and CSV

I have two input files, input.vrt and input.cvs

input.vrt looks as follows:

<OGRVRTDataSource>
    <OGRVRTLayer name="input">
        <SrcDataSource>input.csv</SrcDataSource>
        <GeometryType>wkbPoint</GeometryType>
        <LayerSRS>EPSG:27700</LayerSRS>
        <GeometryField encoding="PointFromColumns" x="X" y="Y"/>
        <Field name="Z" src="Z" type="Real"/>
    </OGRVRTLayer>
</OGRVRTDataSource>

input.csv as follows:

X,Y,Z
385500,815500,2

I assumed that the following command would do all my work:

% ogr2ogr -f csv -s_srs EPSG:27700 -t_srs WGS84 output.csv input.vrt 
-lco GEOMETRY=AS_XY

It does not work however, and I get an error about "Failed to initialize 
PROJ.4 " due to "unknown ellipical parameter name". See the full error 
at the bottom of this email.

I thought that it might be better to separate the file conversions and 
the reprojection and did the following:

First convert:    % ogr2ogr input.shp input.vrt
Then reproject:    % ogr2ogr -s_srs EPSG:27700 -t_srs WGS84 output.shp 
input.shp
Then convert:    % ogr2ogr -f csv output.csv output.shp -lco GEOMETRY=AS_XY

But the reproject step fails on exactly the same error.

Leaving out the -s_srs override, because it is obsolete does not help

% ogr2ogr -t_srs WGS84 output.shp input.shp
(fails on same error)

Finally, it worked using the older 1.6 version of ogr2ogr, which I had 
renamed to ogr2ogr16

% ogr2ogr16 -t_srs WGS84 output.shp input.shp
(now it works)

When I useArcGIS to map the points in both projection they coincide 
exactly. Output.csv looks as follows:

X,Y,Z
-2.240199963394935,57.230193361600563,       2.000000000000000

Out of interest I made the source projection explicit again, and I get 
the same error again:

% ogr2ogr16 -s_srs EPSG:27700 -t_srs WGS84 output.shp input.shp
(fails on same error)

This could be a bug in the new version, but I suspect that I have 
misunderstood how ogr2ogr is really intended to be used.

Could somebody point me in the right direction?

Thanks in advance,

Alex

-- 
Alex Hagen-Zanker
University of Cambridge, Department of Architecture,  1-5 Scroope Terrace, Cambridge, CB2 1PX, United Kingdom
Tel: +44(0) 1223 330573




Full error message:

ERROR 6: Failed to initialize PROJ.4 with `+proj=tmerc +lat_0=49 
+lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy 
+datum=OSGB36 +units=m +no_defs'.
unknown elliptical parameter name
Failed to create coordinate transformation between the following 
coordinate systems.  This may be because they are not transformable, or 
because projection services (PROJ.4 DLL/.so) could not be loaded.
Source:
PROJCS["OSGB 1936 / British National Grid",
    GEOGCS["OSGB 1936",
        DATUM["OSGB_1936",
            SPHEROID["Airy 1830",6377563.396,299.3249646,
                AUTHORITY["EPSG","7001"]],
            AUTHORITY["EPSG","6277"]],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]],
        UNIT["degree",0.01745329251994328,
            AUTHORITY["EPSG","9122"]],
        AUTHORITY["EPSG","4277"]],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",49],
    PARAMETER["central_meridian",-2],
    PARAMETER["scale_factor",0.9996012717],
    PARAMETER["false_easting",400000],
    PARAMETER["false_northing",-100000],
    AUTHORITY["EPSG","27700"],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH]]
Target:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.257223563,
            AUTHORITY["EPSG","7030"]],
        TOWGS84[0,0,0,0,0,0,0],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0,
        AUTHORITY["EPSG","8901"]],
    UNIT["degree",0.0174532925199433,
        AUTHORITY["EPSG","9108"]],
    AUTHORITY["EPSG","4326"]]