[GRASS5] projection-transformation

[Markus Neteler]

Merry Christmas to all!

On Fri, Dec 22, 2000 at 07:40:05PM -0600, Helena Mitasova - staff wrote:
> 
> Here are my examples (sorry that the shift is not
> too visible - it was not my intent to stress it in these images)
> 
> http://www2.gis.uiuc.edu:2280/modviz/wake/demrdstr.gif
> 
> http://www2.gis.uiuc.edu:2280/modviz/wake/ccsoil30m.gif
> 
> DEM and soil data(polygons) seem to fit,
> streams and streets - lines are shifted
> 
> the data are from
> 
> streams are
> EXP  1 G:\DATA\AGENCY\CENSUS\TIGER_DATA\TIGER95\NAD83\WATER83\WTR37183.00
> soils
> G:\DATA\AGENCY\CGIA\SOILSURVEY\NAD83\WAKE\WA83.E00
> DEM is
> F:\TEMP\DATA\AGENCY\USGS\DEMS\NED\BYCOUNTY\WAKE.E00
> 
> there is no projection involved in GRASS or m.in.e00 -
> all imported data should be in the same projection and with
> the same datum.
> So I believe that this is not a GRASS projection problem.
> 
> So it seems to be  something in arcinfo export data that GRASS does not
> understand correctly - are the coordinates relative and
> arcinfo knows that they should be shifted but grass does not?
> Or the shift is already in the arcinfo data and nobody has
> noticed it - I am getting that checked.

Helena, please check this if possible! It would be somewhat crazy if
students in your and in my university do the same error without
knowing each other :-)
 
> At this point I don't remember whether I had this problem
> with shape files (I did a lot of imports for those too - 
> thanks to the developers who contributed the tools! it is now
> much easier to use arcinfo data) but I can check. I have a few more examples
> in several completely different locations - all involve
> shift between the raster data (DEM, Land use) and vector
> line data (streams) imported from arcinfo and the shift is always 
> approximatelly the same.

This is interesting (and a good indicator for a systematic error).

> However I must admit that it may be my problem of importing
> data with different datums (although the ifnormation that I am
> getting with the data says they are the same) or arcinfo problem.
> 
> I will let you know when I find something more concrete about the problem,

Find attached my example with additional data:
 - blue: gshhs data
 - red: ARCINFO digitized data
 - cross: I have read the original Gauß-Krüger-coordinates from a toposheet, 
   projected this point to UTM with m.proj and imported into UTM location
   with s.in.ascii. The UTM coordinates are 377375 5953157.
   
It seems that the GSHHS west corner of the island and my manually read point
match quite well. So the problem could be
 - import problem in GRASS from ARCINFO (obviously m.in.e00, v.in.shape and
   maybe v.in.arc would be affected)
 - ARCINFO is having an internal error (wow, that would be a surprise)

Those having access to *other* GIS vector software - please make a few tests
to see if there is a bug in GRASS, GRASS import or somewhere else.

BTW: I have sent my ARCINFO map to Michel for investigation. Perhaps he can
find the problem in the e00 file (Michel: You have the red line dataset,
above west corner point in lat/long is 7:08:31.53E 53:42:41.51N).

Final test: I have transformed my west corner point to lat/long:
 - it matches gshhs dataset
 - it doesn't match ARCINFO

Again, the proj software seems to be o.k.

Markus
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