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| Subject: | [gislist] SUM: and again how to: Define User Defined Datums in
ArcGIS |
| Date: |
06/07/2005 05:55:01 AM |
| From: |
Vassil Vassilev |
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Hi all and thanks those of you who respond to my
question.
Spatial thanks to Ivan Lucena for the extended
explanation - I will send it soon to others.
Nevertheless I still could not find solution.
That is why I am sending you the txt file which I am
using to project my coverage in ArcInfo/Arc with the
PROJECT command, it looks like that:
INPUT
Projection LAMBERT
DATUM USER_DEFINED 999 888 777 666 555 444 333
Units METERS
Spheroid KRASOVSKY
Xshift 0.0000000000
Yshift 0.0000000000
Parameters
45.01 /* 1st standard parallel
45.02 /* 2nd standard parallel
28.01 /* central meridian
5.01 /* latitude of projection's origin
9999999.01 /* false easting (meters)
0.00000 /* false northing (meters)
OUTPUT
blablabla it could be any projection with known datum.
All of the parameters I could find where to include
them in ArcGIS, but the parameters for the datum I
could not find where to describe them.
In the ArcInfo help it is written:
USER_DEFINED - keyword indicating a set of conversion
parameters will be provided. These are the parameters
necessary to convert between a current datum, to or
from WGS84 using the three or seven parameter
transformation. Enter the parameters as if converting
from the local datum to WGS84. If transforming from
WGS84 to a local datum, PROJECT will modify the
parameters appropriately. Specify the spheroid with
either the SPHEROID subcommand or the semi-major and
semi-minor axis values on the PARAMETERS line.
<dx, dy, dz> - the parameters necessary for a
three-parameter transformation. These are the
differences between the origin of the current or
desired datum and WGS84. Units are meters.
dx - the difference in X.
dy - the difference in Y.
dz - the difference in Z.
{rx, ry, rz, scale} - optional parameters for a
seven-parameter (Bursa-Wolf) transformation. These
represent rotations around the axes, and a change in
scale. The default values are zero. The rotations are
measured counter-clockwise (when looking towards the
origin of the system) in decimal seconds while the
scale change is in parts per million.
rx - rotation in X.
ry - rotation in Y.
rz - rotation in Z.
scale - difference in scale
In my case: dx=999 dy=888 dz=777 rx=666 ry=555 rz=444
and scale=333
These 7 figures are the only one for which I don't
find where to assign.
If I leave datum Krasovsky there is 100 m shift which
do not satisfy me.
I tried to put these parameters in ArcGIS prj file but
without success. The idea is to set this projection to
PGDB and them to reproject the whole PGDB, if I am
using Arc command I could work only with coverages.
I hope now my question is much more clear now and I
will appreciate additional suggestions.
Thanks again,
V. Vassilev
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