+rickrich Posted October 27, 2003 Share Posted October 27, 2003 Dunno if Jeremy realizes this or not, but the scaling of the maps is different in the X and Y directions. The Y direction is compressed by a factor of 0.875. The mileage ruler is correct for the X direction, but incorrect for the Y direction. Link to comment
+brad.32 Posted October 27, 2003 Share Posted October 27, 2003 The maps are in displayed geographic coordinates, so the scale changes with latitude due to increased distortion away from the equator. Other distortions in this representation are shape and area. Link to comment
+rickrich Posted October 27, 2003 Author Share Posted October 27, 2003 Its pretty uncommon to use this type of projection. At least to my eye, its odd to see a perfect square mile, such as Old Towne Orange in Anaheim, displayed as a rectangle. Its not a bug if you document it, just very different than what you see with MapQuest, MS, etc. Link to comment
+Kordite Posted October 31, 2003 Share Posted October 31, 2003 > Its pretty uncommon to use this type of projection. But it is very easy to manage mathematically. You don't have to do all those great circle calculations which I have done by hand and also attempted to program. Let me tell you, it's not fun. Kordite ph34r my l33t kl1n90n 5k1ll5. Link to comment
iryshe Posted October 31, 2003 Share Posted October 31, 2003 I wasn't aware of the difference in x and y, but the distance calculations using Identify use the Great Circle calculation, so they are accurate. Jeremy Irish Groundspeak - The Language of Location Link to comment
+rickrich Posted November 4, 2003 Author Share Posted November 4, 2003 My original guess was that the maps were calculated for a 400x400 square image size, but then mis-scaled by displaying them as a 400x350 image. Thus the 0.875 factor. But this could also be due to an unusual map projection. I haven't done a thorough check to see which is the case. What map projection do you use, BTW? Link to comment
+rickrich Posted November 27, 2003 Author Share Posted November 27, 2003 I took a closer look at this issue and I discovered the actual problem. Take the current 400x350 image at zoom level 7 as delivered by gc.com: Now scale it to 400x500 (this is a scale factor of 1.0/0.7=1.428571 in the vertical dimension only). Now, grab a 400x500 image from the tiger map server at a scale factor 14000:1 with the same center lat/lon. I have verified that the tiger map server delivers maps with equal X and Y scaling by comparing with mapblast and expedia maps. Compare and contrast the images. Other than the eye candy found on the gc.com map, these last two maps now display the essentially same roads and with equal distance in both the X and Y directions. I think you need to revist the map server code and fix the scaling in order to deliver proper maps. -Rick Link to comment
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