Forgive me for not following the whole thread, but are you trying to convert a spherical lat and long to a planar x,y coordinate system? Or are you starting with those distorted maps where Greenland is the size of the United States on a flat map?
Because if you want to use real world maps and data on a flat plane, you'll have to do some more math. There are several ways to do this if you're looking for accuracy. The military and other agencies use UTM. http://www.uwgb.edu/dutchs/UsefulData/UTMFormulas.htm -Lee Jesus Guardon wrote: > Hi Doriano and list > > First of all, many thanks for your input. > > Yes, you are right about geographic coordinates; in real world the > intersection between Ecuatorial line and Greenwich meridian is the > coordinate 0;0. Meridians above increase up to 90 degrees to North and > below to -90 South. By the way, parallels increase up to 180 deg to East and > -180 to West from Greenwich (parallel 0). So the upper left corner (in case > of a whole World map) should be -180;90 and the lower right corner 180;-90. > Based on this, the result rectangle will be 360 units wide * 180 units tall. > > But still is unclear if I can use negative values mapped to a rectangle, as > you appointed in your previous post. The idea is to have a procedure that > can do e.g. drawCoordinate(-3, 40), and draws a point (or whatever I want) > on the correct place. > > Let me play for a while with your program, write some garbage on my notebook > and I will post here my results. Again, thank you for your interest. > > Jesus Guardon > > Gambas 2.9 > > > Doriano Blengino wrote: > >> I've set up a simple project to show how the transformation matrix works. >> It draws a line from (0;0) to an arbitrary point you specify in LX: and >> LY:. >> You can play with Draw.XXX fields to see they effect. >> What I discovered is that (gambas vesion 2.0.0): >> >> 1) For me, negative scalings do not work; this is a *serious* limitation. >> 2) Offsets are multiplied by scaling, ie they are expressed in "real >> world" coordinates. >> 3) Perhaps I am missing something, but it seems to me that you can not >> read what is the current transformation matrix; the program should keep >> track of this. >> >> >> Now, I don't know what "72N" and "-25W" mean (I think north and west, >> but that is all), anyway, supposing that they are arbitrary measurement >> units, then your map is 44+25 units wide, and 72+18 units tall, ie 69 x >> 90. >> You want map this to a 800 x 600. If you don't care about aspect ratio, >> then do Draw.scale(800 / 69, 600 / 90). >> If you want to mantain aspect ratio (it should be), you assign the same >> value to scalex and scaley, the smaller of the two: 800/69=11.59, >> 600/90=6.66, so do Draw.scale(6.66, 6.66). >> As your upper left corner is -25W and 72N, you must do >> Draw.translate(25, -72). >> At this point, plotting a (25; 72) should go to (0; 0) in the drawing >> area. >> From here ahead, I think there is a problem with the computer graphics >> having Y axis pointing to the bottom, so may be your map will be flipped >> up side down. Every Y coordinate should be transformed by newy = >> MapHeight-y, so a different draw.translate() must be issued. >> >> Anyway, it seems to me that the combination of Scale() and Translate() >> does the following: >> >> coordinate_to_plot = (programmed_coordinate + translate_value) * >> scale_value >> >> Hope this is enough - I well could have done lot of errors, but the test >> project can let you experiment. >> >> Regards, >> Doriano >> >> >> >> >> ------------------------------------------------------------------------------ >> SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, >> Nevada. >> The future of the web can't happen without you. Join us at MIX09 to help >> pave the way to the Next Web now. Learn more and register at >> http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ >> _______________________________________________ >> Gambas-user mailing list >> Gambas-user@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/gambas-user >> >> >> > > ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Gambas-user mailing list Gambas-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/gambas-user
