Rotating raster grids using ArcObjects changes cell size in ArcGIS Desktop?

Question

I am using ArcObjects, namely RasterGeometryProc, to apply rotation on grids. The transformation works fine. However, when looking at the grids properties in ArcGis, the cell sizes has changed.

Without rotation, the cell size is 50 X 50 as expected. After applying rotation transformation (30 degrees), I get 72.728 X 64.539.

Seems like the new size is the extent of the rotated cell ?

Is this a bug, or is it the way it is supposed to be ?

Answer 1

I found the answer myself, when interpreting this documentation from ESRI.

Seems like the cell width & height is a part of the transformation (affine ?) parameters for e.g. rotation. The cell "size" is not the size of the cell (except when the raster is not rotated), its the increment factor for each cell's spacing in the XY plane.

• whuber: I don't quite follow: when you rotate a 50 by 50 square cell, the spacing of the rotated rows or columns along any axis cannot exceed 50. Where exactly do the values of 72.728 and 64.539 come from, then? (Those numbers have no evident relationship to a 30 degree rotation, either.)
• Oyvind: @whuber, they are the width/height of the cell, not along the sides, but measured corner to corner from the base x and y axis.
• whuber: Thank you. I guessed that, but those values appear inconsistent with a 30 degree rotation. Perhaps the rotation was not exactly 30 degrees?