File talk:New Madrid Seismic Zone activity 1974-2011.svg
Center coordinates[编辑]
These coordinates are given in the image description:
| Map point | Longitude | Latitude |
|---|---|---|
| Upper-left | -91.402011 | 37.435457 |
| Lower-right | -88.476945 | 34.954139 |
| Center | -89.916299 | 36.204010 |
If you do the math to find the point on the middle of the line between the corners, you don't get the value given here for the center. That is because the map is projected, and the "straight" line between those two corners will be somewhat warped by the projection to polyconic coordinates. For the same reason, I wouldn't expect the lower-left and upper-right corners to not share either of the longitude or latitude of the other two corners.
The corners in the projected coordinate system are actually:
| Point | Easting | Northing |
|---|---|---|
| Upper-left | -168319.361 | 105512.630 |
| Lower-right | 93443.290 | -171041.404 |
| Lower-left | -168319.361 | -171041.404 |
| Upper-right | 93443.290 | 105512.630 |
Note that the corners in this coordinate system do describe an upright rectangle. The centerpoint of that rectangle is at -37438.035500, -32764.387000, which when "unprojected" back into geographic coordinates, gives the latitude and longitude given in the first table for the center of the map.
These coordinate conversions can be observed with this shell command on a system with invproj from the proj4 distribution installed:
$ invproj +proj=poly +lat_0=36.5 +lon_0=-89.5 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs <<_EOF -168319.361 105512.630 93443.290 -171041.404 -168319.361 -171041.404 93443.290 105512.630 -37438.035500 -32764.387000 _EOF
The output is:
91d24'7.238"W 37d26'7.647"N 88d28'37.001"W 34d57'14.902"N 91d20'33.665"W 34d56'40.102"N 88d26'38.366"W 37d26'45.752"N 89d54'58.677"W 36d12'14.435"N
which, converted to decimal format, is equivalent to:
91.402011W 37.435457N 88.476945W 34.954139N 91.342685W 34.944473N 88.443991W 37.446042N 89.916299W 36.204010N
