I think you need to translate and scale by 2 the image_map when you 
use once, because the center of the heightfield is at <0,0,0>
but not the center of the image_map (I think one of its corner is
at <0,0,0>). And you need to scale because the heightfield is
"inside" a box which have edge with 2 for length (go from -1 to 1).
But perhaps I am wrong. I am using Moray and I do like this and I
never had problems but I use material_map not image_map but I
think the process is the same :).

Fabian.


> 
> Maybe others have run into this before, but I've noticed that the two
> bits of code do not render the same way:
> 
> height_field { tga "land_height.tga"
>                pigment { image_map { tga "land_color.tga"
>                                      map_type 0 interpolate 2 }
>                          rotate -90*x }
>                }
>  compared to
> 
> height_field { tga "land_height.tga"
>                pigment { image_map { tga "land_color.tga"
>                                      map_type 0 interpolate 2 once}
>                          rotate -90*x }
>                }
> 
> The second one is the default added by POV-Ray through the insert menu.
> When I render the second bit of code the shadow looks normal, but the
> height field has great patches of transparency. There is no alpha
> channel on either .tga file.
> 
> I've checked this on Mac and Windows, the standard POV-Ray and MegaPov
> on both platforms.
> 
> Is this a known issue or should I submit a bug report on this one?
> --
> Josh English
> eng### [at] spiritonecom
> "May your hopes, dreams, and plans not be destroyed by a few zeros."

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