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# Plotting geographical coordinates to a map

Posted on 2003-12-05
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Hello
I would appreciate any help on the following question:
I need to convert geographical coordinates (Latitude and Longitude) to x,y coordinates, and display a text box (or label) on a form (ms-access) at the appropriate position. (The map is a bmp image of Europe).
Many thanks in advance.
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Question by:Bernard_AC
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LVL 44

Expert Comment

ID: 9884580
what PROJECTION has been used to create the map of Europe.?

In general, it is NON-TRIVIAL exercise to transform Lat-Lon into X-Y.

AW

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Author Comment

ID: 9884990
The map is a simple bitmap image of Europe - I don't know how it was created, or on what scale.
If I'm reading your query correctly, do I understand that you are asking if there are preset coordinates (or points of reference) on the bitmap image? Thanks.
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LVL 44

Expert Comment

ID: 9886027
no.  When a map is made, adjustments must be made to convert the curved surface of a globe to a flat surface.  This is called the projection.  For instance, most maps in an Atlas use the MERCATOR projection, which has the effect of stretching the map EAST-WEST as you move away from the equator.  But there are many other projecte ion that might be used, and each of them has a different way of convertin latitute and longitudfe into rectangular coordinated (X-Y).  Without knowing the projection involved, you woul be simply guessing.

The fact that you have a bitmap means absolutely nothing.  You could gues if you know the latitude and longitude of each of the four corners of the map.  YOu could then interpolate to get the location of any other point on the map, but that would be quite crude, and approximate.

AW
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Author Comment

ID: 9887562
OK - that's pretty much the line of thought that I had established. Unfortunately the project I am working on has me limited to maps that the cust already has in use. So I guess that I will end up trying to approximate, after working out the lat and long of the corners. Just out of curiosity, do you happen to know of a good source of MERCATOR projected maps (Political) which I could get hold of? Many thanks for your help.
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LVL 44

Accepted Solution

Arthur_Wood earned 250 total points
ID: 9889819
not right off the top of my head.  Try GOOGLE.

AW
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Author Comment

ID: 9892158
That's where they got the maps they use. I guess I'll try to work around the flat projection issue, perhaps by using some kind of meridional part correction.
Many thanks for your input.

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