Vector to Raster conversion
Hi,
I have a point Shapefile that I would like to recreate in raster, specifically, ESRI Ascii Grid format.
However I am having issues in that when I use the 'NumericRasterizer', some of the resultant cells in the raster are up to 0.25m away from the original location of the points. Is there any way that I can set the rasterizer (or use a different transformer) to force the resultant cells to be overlaid exactly on the original points (ie: points will lay in the centre of the cell)?
Thanks
Hi @aquamarine, I think the NumericRasterizer with your setting creates desired raster if the original points form a grid with spacing 0.5m x 0.5m. How did you confirm that the center of cells in the resulting raster have been moved 0.25m from the original points?
I realize now that the issue was that my original point shapefile was not evenly gridded at 0.5m intervals and that's why I wasn't getting the NumericRasterizer to work. I will need to recreate the point shapefile with 0.5m intervals.
A possible source of the issue could be that the raster cell size isn't exactly the same as the point spacing. Here's what it looks like if we use Takashi's example and set a raster cell size of 0.55 while retaining a point spacing of 0.5:
Notice how the points "drift" compared to the raster cells, eventually crossing into the neighboring cell.
Another thought. Once set the cell origin to (0, 0) and then transform the raster into grid points with the RasterCellCorecer, the resulting points match left-bottom corners of the cells. It seems that FME reads an Esri ASCII Grid raster with cell origin (0, 0), so I think this is also a possible situation.
Anyway, let's wait for @aquamarine's response.
Can you show us how you've configured the NumericRasterizer?
- Calculate the extent (bounding box) of all your points
- Divide the totalt extent into a grid of 0.5 x 0.5 meter large cells
- If a point is inside a cell, the cell gets the value from the point
So unless your points are all perfectly lined up in accordance with the grid, you'll often get these effects.
One way to mitigate this problem could be to set a user-defined ground extent in the NumericRasterizer and do a slight offset compared to your point extents, e.g. half a cell off (-0.25).
Have you looked at the MapnikRasterizer?
I find that one easy to use.
I tried the MapnikRasterizer but I am getting the following error:
REJECTING BELOW FEATURE: Polygon feature must have at least 4 coordinates...rejecting
I am importing a point shapefile not a polygon file. Is there a way to set it so that it knows I am importing point data.
Have a look at this document: MapnikRasterizer
