[postgis-devel] [PostGIS] #495: [wktraster] Don't seem to be able to specify non- 0 skews in ST_SetGeoReference

[PostGIS]

#495: [wktraster] Don't seem to be able to specify non- 0 skews in
ST_SetGeoReference
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  Reporter:  robe       |       Owner:  pracine        
      Type:  defect     |      Status:  assigned       
  Priority:  medium     |   Milestone:  WKTRaster 0.1.6
 Component:  wktraster  |     Version:  trunk          
Resolution:             |    Keywords:                 
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Changes (by pracine):

  * status:  new => assigned

Comment:

 I fixed st_setgeoreference so now it accept minus numbers.

 skew/rotation is not in gradient nor in degree. The doc on world files and
 the 4 first parameters is really misleading. I uploaded a graphic in the
 wikipedia page for world file trying to show graphically the different
 parameters. Some call the D and B parameters "skew" but I am not convinced
 by this terminology. I would prefer:

 A is the x component of the pixel width,
 D is the y component of the pixel width,
 B is the x component of the pixel height and
 E is the y component of the pixel height.

 D and B are equal to 0 when the raster is not rotated.
 A is equal to -E when the pixel are squares.

 There is nothing such as a rotation in angle but we can derive it from
 those parameters and we can derive those params from a provided angle.
 This is the intent of the planned ST_Rotation() and ST_SetRotation()
 functions.

 I will rename the actual ST_Rotation() to ST_Skew()...

 I hope my graphic makes all this clearer. You can use it wherever you
 want. I might also update the text of the article.

 I updated the spec about ST_Georeference.

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/495#comment:2>
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