[GRASS-user] null values and v.surf.idw

GRASS GRASS user
1

Dear people,

I’m interpolating some data by means of v.surf.idw. I loaded data in a
database using v.in.ascii and create a vector layer. Here is an example of
five loaded fields of one row. X and y coordinates are in the two first
columns. Other fields are data to interpolate. But some stations missed some
data. So, the imported database contains blank values whenever data is not
available. This row has blank (no data or null) values in data2:

X;y;data1;data2;data3

623649;4784544;2.3;;1.98

I have no problems using data1 and data3 in v.surf.idw procedure. The
problem appears when trying to use data2. It seems that the interpolation
procedure takes “0.0” value when it should not consider anything. How can I
manage null (no data) in v.surf.idw?

Thanks in advance

Javier Álvarez Rodríguez

Área de Hidrología del Centro de Estudios Hidrográficos del CEDEX

Paseo Bajo de la Virgen del Puerto, 3

Madrid 28007. España

+34 91 335 79 38

+34 91 335 79 22

javier.alvarez@cedex.es

2

Javier Álvarez Rodríguez wrote:

Dear people,

I’m interpolating some data by means of v.surf.idw. I loaded data in a database using v.in.ascii and create a vector layer. Here is an example of five loaded fields of one row. X and y coordinates are in the two first columns. Other fields are data to interpolate. But some stations missed some data. So, the imported database contains blank values whenever data is not available. This row has blank (no data or null) values in data2:

X;y;data1;data2;data3

623649;4784544;2.3;;1.98

I have no problems using data1 and data3 in v.surf.idw procedure. The problem appears when trying to use data2. It seems that the interpolation procedure takes “0.0” value when it should not consider anything. How can I manage null (no data) in v.surf.idw?

I had a similar problem recently and the mailing kindly suggested a solution that worked out. Please see:

http://article.gmane.org/gmane.comp.gis.grass.user/16380/

Hope it helps,
Luigi