[GRASS-user] Correctly Converting LL to LCC

[Rich Shepard]

On Tue, 29 Dec 2009, Glynn Clements wrote:

> 	242807.02 / 796758.58 = 0.3047435272049408
> 	397955.05 / 1305792.74 = 0.3047612670905185
>
> These look suspiciously close to 0.3048 (foot/metre conversion).

Glynn,

   You and Hamish point out that the problem is with conversion of the units:
feet vs. meters. What I'm trying to understand is why there is this problem
and what to do about it.

   The imported Long/Lat location is PROJ_UNITS of degrees, which is what I
would expect. The location with the other maps has PROJ_UNITS of meters.
Therefore, when I run v.proj to convert the ll map coordinates in degrees to
lcc coordinates in meters, why do I end up with feet instead? I see no
length unit option in either v.proj or cs2cs. My assumption is user error,
and I'd like to learn what error I made so I don't repeat it in the future.

   Hamish suggested I scale the units using v.transform. I tried this with
both xscale and yscale at 0.3048 as well as 1.0/0.3048 but neither resulted
in units within the appropriate range.

   It may be that all my maps from the state GIS data repository are
incorrect because soils data from a different agency also cannot be
overlaid. Since I used the ArcView .prj and Arc/Info .e00 files for the
projection and boundary information I need to learn what I've done
incorrectly so I can re-import all these data and be able to move ahead.

   If someone will work with me off the list to get straightened out I would
greatly appreciate it. I have a 2-page .pdf showing the Oregon data library
formats and projection information. Since these data are in International
feet, I need to understand why the PROJ_UNITS are in meters. With someone's
gracious help I can get all this done today and return to being a happy
camper.

Rich