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How world files are used

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GPSJane
1641 Views, 2 Replies

How world files are used

Could someone in the know tell me how world files are read and used by software. Obvously the image is positioned and scaled to fit the coordinates but is the image also rotated? Is it rubber sheeted?

 

Can I save my images only in their original format, without any rotation or rubber sheeting and let autoCAD do it when importing the image using the world file?

 

For that matter, when AutoCAD asks to save my image changes to images, if I don't will the image not be rubbersheeted later on when I open it again? Or can I leave it like that and will the software 'remember' how to place it?

 

Basically the person before me saved every image again in it's 'rectified' form but I wonder if that is really neccessary, expecially if I just export the world files as I have to do anyway.

 

 

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Message 2 of 3
parkr4st
in reply to: GPSJane

fairly good explanation  web search world file you will find more

 

http://en.wikipedia.org/wiki/World_file

 

A world file postion the image usually at the top left pixel or center of the top left pixel and rotates it.  The CRS will determine the x.y of the ulp.

 

saveimg gives several file type options

 

Raster command    iexport      gives choices of file type and lets you set a world file also

 

 

For that matter, when AutoCAD asks to save my image changes to images, if I don't will the image not be rubbersheeted later on when I open it again? Or can I leave it like that and will the software 'remember' how to place it? 

 

Unsaved image will be unchanged as the file is reloaded as is.

 

Rectified as rubbersheeted and rotated to fit?  I would think rotated yes, rubbersheeted no.  Save to a new image file with the new world file to be sure.

 

If the scope of the project is to take somebody elses work and put it order, I would save everything in an order where I could find everything when I needed it and know it is correct.  new directory folders apart from any of the old data.  As I rambled yesterday, accuracy and precison plus if you can find the right data at the right time you look super at presentation time. 

 

dave

 

Message 3 of 3
GPSJane
in reply to: parkr4st

Thanks Dave

 

It would be great if full transformation could take place based on several coordinates.

 


@parkr4st wrote:

 

Unsaved image will be unchanged as the file is reloaded as is.

 


Do you mean reloaded into the same place with rotation and scale, or reloaded and inserted as with a new image (with new coordinates, scale and rotation)?

 

The reason I ask is because I seem to have lost some raster images in the file I am currently working on.

 

In relation to your question, I am carrying on work from where the last person left off. So I edit files already created, create new ones and fix problems in the old ones too. I am setting up standards and what not but at the same time I need to finish work in between. It makes it hard to sit and move files or change standards or learn new things. I will redo the filing system but at the moment I still can't get the project search path to find raster images correctly. Then I need to reinsert the image and sometimes the world file seems way out so I end up doing double the work.

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