Smooth lines between raster values

chrisechrise Global Mapper UserPosts: 21
edited October 2009 in Raster Data
Dear Forum,

I have a raster dataset that is classified at 4 intervals. The cell size is 50m.
I am trying to work out the process that Globalmapper employs when it renders the raster once I have applied my colour ramp - in terms of the smoothing between the values themselves.. (see attached jpeg)

ie. in the attached image you can clearly see the pixellated effect which depicts the edge of the raster surface.

Why are the boundaries between the raster values themselves not pixellated? What is the smoothing algorithm that is applied?

Thanks in advance,
Chris

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited September 2009
    Chris,

    It looks like you have anti-aliasing (bilinear interpolation) enabled for the layer on the Options dialog for it accessible from the Control Center. This will use bilinear interpolation to smooth out any values between 4 adjacent cells (pixels). This interpolation does not change the shape/size of a cell though, so your boundaries will still be sharp at pixel boundaries. No part of a missing/no-data cell (pixel) will be shown.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • chrisechrise Global Mapper User Posts: 21
    edited October 2009
    Mike,
    Is there a smoothing algorithm that Globalmapper applies also? Running the raster through a bilinear interpolation using a different tool does not produce the same effect?
    TIA
    Chris
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited October 2009
    Chris,

    Global Mapper currently only uses either nearest neighbor sampling (the default for raster layers) or bilinear interpolation (anti-aliasing). The bilinear interpolation only works between valid cell values. If your location is inside a cell with no data, nothing will be shown in that cell even if there are adjacent cells with valid data. This is why you see the pixelated edge result Rather than some sort of smooth curve.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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