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| GeoCommunity Mailing List |
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| Mailing List Archives |
| Subject: | RE: GISList: Satellite Maps |
| Date: |
03/17/2003 10:17:20 AM |
| From: |
Bannerman Bruce |
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Hello Mohamed,
For a precise defininition, you would be better off referring to a Remote
Sensing or Digital Image Processing text book. There are several good ones
available.
In answer to your questions:
1.
In simple terms, the term *image accuracy* can refer to:
- The positional accuracy of an image. That is, how close is a pixel to its
'true' location with reference to a spatial reference system (ellipsoid,
projection, datum, and possibly cartesian coordinate system).This would be
the usual context of the term.
- Image accuracy has also been used to refer to how closely the spectral
signature matches conditions present at the time the image was captured.
*Image resolution* normally refers to the size of individual pixels in an
image. For example Landsat TM is often quoted at 30m resolution and Spot 4
Panchromatic at 10m resolution.
In the case of the Spot 4 Panchromatic example, each pixel can be thought of
as covering a rectangle 10m by 10m on the ground.
We need to be careful when considering the resolution of an image as it is
very easy to resample an image to a higher or lower resolution. In the case
where an image is resampled to a higher resolution, we do not improve the
quality of the image.
2.
In my opinion, satellite images are definitely suitable for map production.
You have a choice of spectral bands that with analysis can be used to help
illustrate a point. Or satellite images can be used in much the same way as
aerial photographs traditionally are, by displaying visible light bands.
The decision to use satellite imagery or aerial photography is based on many
things and usually project driven. For example the following may be
considered:
- What is the purpose of the map (what information is to be conveyed)?
- What accuracy is required by end users?
- What is the resolution of the available images?
- What is the cost of acquiring the data and can the cost be justified
economically?
In many cases, particularly in smaller scale mapping, satellite imagery
offers an attractive alternative.
I feel that two factors that have been inhibiting the use of high resolution
satellite imagery are:
- Cost: and
- A lack of understanding of the capabilities of digital image processing.
3.
This needs to be judged on a case by case basis.
I hope that this helps.
Regards,
Bruce Bannerman
GIS Strategy Officer
City of Melbourne
Australia
> -----Original Message-----
> From: Mohamed Eleiche [SMTP:meleiche@link.net]
> Sent: Wednesday, March 12, 2003 4:37 AM
> To: gislist@geocomm.com
> Subject: GISList: Satellite Maps
>
>
> Hello Everyone,
>
> Relating to the raster issue,
>
> I need some precis definitions :
> ----------------------------------------
>
> 1)What is the meaning of image accuracy & image resolution ,
> and what is exactly the difference between them ?
>
> 2) Why high resolution satellite images are not suitable for
> map production specially large scale ?
>
> 3) What is the difference between maps produced from
> satellite images & those produced from aerial photos ?
>
> Thank you in advance,
>
> Best Regards,
>
> Mohamed Eleiche
> GeoTiba Systems
> P O Box 17
> Zamalek, 11211, Cairo,
> Egypt
> Mobile +20 10 147 9703
> Tel/Fax +20 15 383720
>
>
>
>
>
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