Laurent,
I saw your attached mail and was worried about what you are trying to do
and the apparent accuracies involved.
I am not an expert but you should look deeper at the accuracy levels you
require. Registering on four points and getting 0 error gives a comfort
factor that does not necessarily reflect the reality.
If you are trying to 'heads up' digitise from a satellite image you should
be using a minimum of 9 points((corners and middles) and more if possible)
as there are inherent distortions due to the method of acquisition, think
about it - a scanner bar moving across a flat plane image on a moving
platform of a moving target from >600 Kms.
>From what I have read and seen, the distortion is in an 'S' shape along the
line of flight.
You don't mention what imagery you are using nor the resolution, depending
on the imagery , you should only consider creating maps of down to specific
scales i.e.
|-+-+---+--+---++|
| | | | | |||
| SPOT XS | France | 20 m| VIS| 60 x 60 ||1 : 100 |
| | | | |km²||000 |
| | | | | |||
|-+-+---+--+---++|
| | | | | |||
|PAN | | 10 m| PAN| || 1 : 50 000 |
| | | | | |||
|-+-+---+--+---++|
I hope this is of help
Ian Rudd
"MAPPER MAN" <[EMAIL PROTECTED]>@lists.csn.net on 23/03/2000 13:06:31
Sent by: [EMAIL PROTECTED]
To: [EMAIL PROTECTED], [EMAIL PROTECTED]
cc:
Subject: Re: MI problem with raster image
As i know you have to increase your raster image resolution at leat 1 m
resoltion if u r using UTM, Lambert or other projection systems im sure u
dont have any problem with lan/lon system :)
Have nice Day
Mapper Man
>From: "laurent Frilleux" <[EMAIL PROTECTED]>
>To: <[EMAIL PROTECTED]>
>Subject: MI problem with raster image
>Date: Thu, 16 Mar 2000 16:28:49 -
>
>hello,
>
>I have a problem for digitalizing roads.
>I have a big satellite image (7500*7500 pixels) with 4 points and error
>pixel is 0.
>When i digitalize, i have no problem, but when i change the zoom level,
>polylines are moving definitively and i i qo back to the initial zoom
>level, they are not at the rigth place.
>
>I have try to add some points, it's better but the problem still exist
>I have change the projection , no change
>i am trying to split the image in severals..
>I have reduced the bounds in the table, it's bettre but the problem still
>exist
>
>
>thanks in advance
>
>
>Laurent frilleux
>STRATEGIS
>MONTPELLIER
>0467416841
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