Question : urgent mapinfo & arcgis

Dear Friends,

I have an urgent question.How can i register my raster map in MapInfo & ArcGIS, to have a real gps coordinate?
I have a 5 points know with GPS coordinates.
Thank you all.

Cheers,

Answer : urgent mapinfo & arcgis

To georeference Images(in BMP , TIFF and JPG) you need to know at least three points......

First step is to note the X,Y of the three points for which you have Lat/Long information. This can easily be done by using
any Image Package(Photoshop, Paint etc.).
Now take the point with the Least Longitude and name it as point 1 having (x1,y1) and (long1,lat1) .
Take the point having the Max. Longitude and name it point 2 (x2,y2) and (long2,lat2)
and the point having Min. Latitude as point3 (x3,y3) and (long3,lat3)
similarly Max. Latitude as (x4,y4) and (long4,Lat4)

Now your delx ( deg./Pixel in X direction) will be
   delX= (long2-long1)/(x2-x1)
similarly
   delY= (lat4-lat3)/(y3-y4)

Now the only thing left is to calculate the Lat/Long of any reference point. So we take the Top Left point as the Refernce point........
It will be calculated using

lat0= Lat4+y4 * delY
long0= Long1 -x1 * delX

and you are done.........


Now your world file will be like this

delx
0
0
-dely
long0
lat0

Now if your map is lets say abc.bmp then when you have a file named abc.bpw in the same folder as the bmp file with the above text then whenever you open the raster Image in ARCView (maybe in ARCGIS too) it will show real GPS coordinates...
If something is not clear then please do post it here......



You can also do it programatilcally as follows



Now (lat/Long) of any point on the image can be mapped on the image using
X= (lat0-lat)/delX
Y= (long-long0)/dely

or conversally X,Y can be converted to Lat/Long using

Lat = lat0-X * delX
Long= long0+Y * delY

I hope this will solve your problem....... You can use a Visual Language (VB or VC) and implement this within an hour or so.......
                                                                                                      Imran Arshad