[MAPSERVER-USERS] raster tiling of non rectangular images

[Pål Kristensen]

Hi!

To my knowledge a raster (or image) is always rectangular (you can have non
square pixel though) . If the actual content is not rectangular, the
boundary is filled with "some other data". You have a couple of choices on
how to handle this.

1. Use the OFFSITE keyword in the layer object to "exclude" a certain pixel
value, e.g  OFFSITE 0 0 0
2. Use gdalwarp to mask no-data areas with a alpha channel

I don't think it would make any sense to add non rectangular boundary
polygon to the tileindex,  because MapServer only uses the tileindex to
determine which raster tiles to draw, no clipping is done (am I wrong??). It
is the actual raster files that is processed, and they would still have the
no-data pixels.

Regards,
Pål Kristensen


victor valencia-2 wrote:
> 
> Hi:
> 
> I need  to create a tileindex of several non-rectangular raster images. I
> tried GdaltIndex, but produces rectangular polygons including the non-data
> (Null) pixels. 
> These images i have are Landsat 7 saved as *.img, *.tiff, *.Sid. 
> These images are rhomboidal. Since the file is rectangular there is an
> area with no valid pixels (non-data or Null). I need a boundary polygon
> that exclude this pixels. 
> 
> I found an arcview 3x extension named Grid to Valid-pixel Polygon Catalog
> w Stats, that creates a boundary polygons of the valid pixels, but works
> just with Grid images. I could change the format of my images but this is
> very very time consuming. 
> 
>  Is there any script to create irregular bounding polygons
> (non-rectangular) from the valid pixels for several images?
> 
> Best regards
> 
> Victor
> 
> 
> 
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