What is the unit of smoothing in gdal_grid?

Question

I am using the gdal_grid command line with invdist algorithm and would like to spedify a smoothing parameter but I am wondering whether it shouold be in pixel or data units (meters in my case)?

I've found the following related links :

• gdal_grid
• GDALGridInverseDistanceToAPowerOptions

but none is clearly specifying the unit.

Answer 1

From looking at gdalgrid.cpp it seems that the smoothing parameter should be in units comparable to the coordinate system, not the raster grid.

// line 165
for( GUInt32 i = 0; i < nPoints; i++ )
{
    double dfRX = padfX[i] - dfXPoint;
    double dfRY = padfY[i] - dfYPoint;
    const double dfR2 =
        dfRX * dfRX + dfRY * dfRY + dfSmoothing * dfSmoothing; //<--- HERE

    /* stuff */

    // Is this point located inside the search ellipse?
    if( dfRadius2 * dfRX * dfRX + dfRadius1 * dfRY * dfRY <= dfR12 )
    {
        // If the test point is close to the grid node, use the point
        // value directly as a node value to avoid singularity.
        if( dfR2 < 0.0000000000001 )
        {
            *pdfValue = padfZ[i];
            return CE_None;
        }