[Qgis-user] Interpolation plugin

[Viktor Kolesnyk]

Hi!

I was using Arc/Info under Windows XP and now I migrated to Linux Gentoo and
want to migrate to QGIS.

One of the tasks I used Arc/Info for is *height (elevation) matrix creation*.
I have polyline and point layers as sources. The former layer is more
accurate.
In Arc/Info I did it in two steps:
1) TIN creation from polyline layer. I also use a territory polygonal layer
to limit interpolation borders (so called '*soft clip*').
2) Convert TIN to Raster (in Arc/Info Binary Grid, *.adf) with 100*100
meters cell size.
As a result I had 547 Mb raster layer *.adf file and some smaller
informative *.adf files.

I read QGIS 1.3.0 user guide and Marco's "Terrain Modelling with Triangle
Based Free-Form Surfaces" thesis and
as I understand there is only possibility to use point layers to create TIN
in QGIS?!
So, I tried this functionality in QGIS 1.4.0 under Gentoo Linux.
I projected my point layer from Geographical Coordinate System to Projected
CS (WGS84).
Then set it as the source in Interpolation Plugin window and chose 100*100
(as I understand in meters) cell size of output layer.
I don't know which format QGIS saves TIN in and there is no filters of file
extensions in "Save interpolated layer as..." window.
So, I simply chose "tin.adf". As a result of interpolation I have 2,5 Gb
file, that seems to be less accurately than my 547 Mb Arc/Info Binary grid
one.

Some questions:
1) Is there a possibility in QGIS to use *polyline *layer as a source of
interpolation (TIN creation)? If no, is it possible to add this
functionality in the future?
2) Is there a possibility in QGIS to *limit* interpolation borders by
another polygonal non-heights layer (such as Arc/Info 'soft clip')?
3) What is a dimension of cell coordinates? Are they use the same units as
projected point layer units?
4) Which format QGIS saves TIN in?
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