[gdal-dev] Help with gdal_grid

[Tim Robertson]

Hi all,

I am a complete newbie and trying to generate a geotiff from point
data in csv but am not able to generate a valid geotiff.

I am using:
$ gdalinfo --version
GDAL 1.7.2, released 2010/04/23

The CSV is of the form:
  Latitude,Longitude,Cell id
  -71.829,-40.6,6619
  -68.9414,-50.3435,7689
  -68.9414,-50.3435,7689
  -68.9397,-50.2087,7689

and I have a VRT:
  <OGRVRTDataSource>
    <OGRVRTLayer name="puma">
        <SrcDataSource>puma.csv</SrcDataSource>
        <GeometryType>wkbPoint</GeometryType>
        <!-- not entirely sure what the z is for but ultimately want
to set color based on number of points in grid-->
        <GeometryField encoding="PointFromColumns" x="Longitude"
y="Latitude" z="Cell id"/>
    </OGRVRTLayer>
  </OGRVRTDataSource>

When I run it I do:

$ gdal_grid -a invdist -txe -180 180 -tye -90 90 -outsize 400 400 -of
GTiff -ot Float64 -l puma puma.vrt puma.tiff
Grid data type is "Float64"
Grid size = (400 400).
Corner coordinates = (-180.450000 90.225000)-(180.450000 -90.225000).
Grid cell size = (0.900000 0.450000).
Source point count = 787.
Algorithm name: "invdist".
Options are "power=2.000000:smoothing=0.000000:radius1=0.000000:radius2=0.000000:angle=0.000000:max_points=0:min_points=0:nodata=0.000000"

0...10...20...30...40...50...60...70...80...90...0...10...20...30...40...50...60...70...80...90...0...10...20...30...40...50...60...70...80...90...0...10...20...30...40...50...60...70...80...90...0...10...20...30...40...50...60...70...80...90...0...10...20...30...40...50...60...70...80...90...100
- done.
$


But the resulting file is not a valid geotiff (Mac preview and
Geoserver are unable to open it)

This really is my first venture into gdal, so any assistance would be
very gratefully received.

Many thanks,
Tim