# [GRASS5] projection-transformation

Markus Neteler neteler at geog.uni-hannover.de
Thu Jan 11 12:24:13 EST 2001

```Hi Michel,

On Thu, Jan 11, 2001 at 03:49:29PM +0000, Michel Wurtz wrote:
> Markus Neteler wrote:
> >
> > Hi Michel,
> > I have received another SHAPEfile with borders which matches quite good
> > to my other data. So three options are there:
> >
> >  - mistake done by the students
> >  - e00 needs Xshift and Yshift set
>
> Well, this is probably easy to handle, but I need some example for
> this (the questions is : does we apply shift before or after scaling ?)
>
> >  - general ArcInfo problem (btw: it was PC3.5, not 8)
>
> For the two other options, I can't do anything ;-)

I have investigated some more hours...

Here the results:
- we have used "projectdefine" to add a projection in ARCINFO8
(using the PC-ARCINFO3.5 e00 file)

-> import into GRASS is identical. The misplacement is *non-linear*.

While thinking about the problem I should describe the input dataset better:
The students have digitized the country's border from a 1:500000 paper map
of Lower saxony. Problem with this map is:
- the map is projected in Lambert Conical projection (10:30E meridian)
- the border's coordinates are given in degree, nothing else
- ellipsoid is "international"

Now the students have referenced the map to lat/long and digitized.
The misplacements are like that (compared with an other digital governmental
dataset and the GSHHS shorelines):

6°         7°         8°         9°        10°        11°
+          +          +          +          +          +  53:30°
north sea    ***(islands)  ***                  -----
***   ----------------   /--------------/       \
*** --------/               |  /                        \
/--/                        \---                          |
|   shift: 2.5km to E                                     |  + 53 E
|          500m  to S
|                                                 shift: +/- 0
|
|
/                   LOWER SAXONY (northern Germany)
|
|                                                              + 52 E
|                                                            |
\    shift: 1km to W (!)                                     |
\          0 to S                                           /
\                                                          /
------------\             /-----\                      /
\           /       \                     /
\         /         \                     /
---------|          \                   /
\                 /
\----------------/
shift: 1.5km to E      + 51 E
2km   to S

Let me say: I am slightly confused.
Perhaps the problem is that the map's projection is Lambert, but GRASS
et al. treat is as Geographic (lat/long)? But, then, how to get in
a map projection in Lambert if only lat/long coordinates are printed on
that map?

I am quite in the dark,
help is appreciated (especially to save the digitizing work)

Thanks for listening!

Markus

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