Aaron,
The distortion that your are describing is the result of the grid being in a
projection that uses longitude and latitude as its coordinate units. The
source of the distortion is that in these projection systems the distance in
the X direction is different than it is in the Y direction (lines of
longitude converge at the poles). Therefore if you were to represent a one
degree by one degree area with a single grid cell the cell must be
rectangular, however Vertical Mapper grids can only square cells. The
distortion that you see is the result of MapInfo modifying the vector
information to match the raster. You can achieve similar kinds of distortion
by registering an aerial photograph that is not orthorectified.
Fix:
Use the Reproject utility and convert the grid to a projection that uses
linear measurements. For California try Universal Transverse Mercator
(NAD27 for US) Zone10.
James Harvie
Vertical Mapper Product Manager
Northwood Geosience Ltd.
43 Auriga Drive, K2E 7Y8
Nepean, Ontario, Canada
613-224-2020
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Aaron Queheillalt
Sent: Tuesday, November 30, 1999 11:54 AM
To: [EMAIL PROTECTED]
Subject: MI DEM Distortion of California
I have the 30 meter USGS DEM's of California which have been converted to
grid with the DEM2Grid in VM 2.0. There are approx. 70 individual
files(.TAB) that cover California. I would like to have a dipiction of the
state with it being Hill shaded with a color pallette applied based on
elevation. The problem occurrs when I open all the files that cover the
state. With all the files open, California get squished, it becomes shorter
and wider. The state looses approx. 1/8th of its original height and gains
a bit in its width. Does anyone know why this may be happening? Is there
any type of fix that can be used. I am fairly new to the world of raster
images and Vertical Mapper, but am very anxious to get this done.
Aaron Queheillalt
916-654-0768
email: [EMAIL PROTECTED]
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