I can't seem to get rid of them, and I've no idea (ok scrap that, I have a vauge idea) whats causing them.
First an apology, yes this is quite a large pic apologies, but here goes:
How to reproduce
Ok, so how did I end up with that.
1) I downloaded the ess-sh meridian 2 map from the OS Open data site
2) I unpacked the archive, and got the 'gridded height' folder
For the purposes of the image above, I only used the files in the NZ folder for now (I intend to do the entire UK once I perfect my method
3) I used the QGis shape merge tool to combine all the shape files in the NZ folder into one large NZ grid of height points, each point is 200 meters apart (According to the measure tool)
4) I then loaded the combined shape file into QGis, and did a visual inspection, each tile of points lined up perfectly, with no strange gaps (One tile starts 200 in from the edge of the tile, and the previous stops 200 after (That is it stops right on the grid square boundary (I've checked this using the OS grid locator shapes and everything is lined up on the boundaries using OSGB36)
5) I then used the QGis interpolation tool, with the following settings:
Input layer : My NZ layer of gridded points
Interpolation attribute : Height
Interpolation method : TIN
Num of columns : 10000
Num of rows : 10000
Cell size X : 9.98000 (Auto)
Cell Size Y : 9.98000 (Auto)
X min, Y Min : 400100, 500100 (Min extents of entire NZ area)
X max, Y max : 499900, 599900 (Max extents of entire NZ area)
6) Hit ok and waited for the raster to render, the result you see above.
What I suspect
I suspect that the bands are some artifact of the shape-file joiner either not joining the source files correctly, or the data in the grids not being what I expect it to be.
However, IF there is discrepancies in how the OS has mapped these (and it wouldn't be the first time) then looking at the boundaries of the sources pre merge, I believe that I should also see these bands running vertically too.
If anyone has any thoughts, I'd appreciate to hear them.
I'm putting this down for the night now, but I'll come back to it over the weekend.
Cheers
Shawty