User talk:Rhalden

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[edit] Plotting coordinates on Winkel-Tripel

Can you suggest any discussion on plotting coordinates for this projection? - Amgine 19:15, 22 November 2010 (EST)

Hi, I hope that this helps...the Winkel Trippel projection is only used for world maps. As it is not conformal, i.e. the map scale is different for latitude and longitude. I would plot coordinates by using linear interpolation along both lines of latitude and longitude. So, measure the distance between two latitude lines, say 10 degrees apart, perhaps this distance is one inch. So each degree of longitude corresponds to one tenth of an inch. Do the same for two lines of longitude, and you'll see the scales are different. Once these scales are determined, you can use them to measure the coordinates of any point from the reference lines. For this purpose I like to use 10-point dividers. They're pricey, but if you do this kind of work a lot (as I once did creating groundwater gradient maps) they'll save a lot of time. But, an ordinary ruler works too! http://www.amazon.com/Weems-Plath-Marine-Navigation-Divider/dp/B000IMYY1Q

Unfortunately, the maps I need to plot on are digital, specifically this 1200x600 and this 800x400 pixel maps. (The images are satellite infrared data generated every 6 hours.) I'm trying to plot locations of cities for which I have weather forecasts; there are several hundred locations, for each of which I have lat/lon, and it needs to be done every 6 hours, so of course I wish to automate the process. What I don't know is how to go from lat/lon to image coordinates.

Based on your comments above, at 0 longitude each degree of latitude = approximately 3.3 pixels, and at 0 latitude each degree of longitude = approximately 3.3 pixels. Unfortunately, 49.24966x-123.11934 (Vancouver, BC) would translate to 162.523878x-406.293822, but in the graphic it is closer to 287x-358. So I'm trying to figure out if there is a mathematical formula which can be applied to lat/lon? - Amgine 23:41, 22 November 2010 (EST)

I'm probably not the right person to ask. I don't know what type of GIS software you're using, but doing this should be fairly easy if your base map is georeferenced. However, given the volume of work you've got on your plate with these frequent updates, I think that you'll need to write a script to accomplish this. Good luck!