GEOTIFF Map Saving
The GEOTIFF save menu choice on the file menu of a map window
saves the current map as a GEOTIFF file.
- You can save as a color image, or a grayscale, which will be computed
from the RGB values on the map image. Grayscale will be about 1/3
the file size.
- The resulting saved image contains map coordinates;
each point on the resulting map is correctly registered,
provided the program that reads the file implements the
- It does not write a TFW
world file. Some programs that claim to read GeoTIFF
files actually use world files.
- The resulting image is a "dumb
picture". It does not know anything about
elevations or the details of any overlays on the map. You
will get exactly what is on screen, at that resolution.
If you have blown up or subsampled the data, that is the
resolution that will be saved. If you subset the data,
only the subset is saved.
- You should reopen this geotiff only to view the previous
analysis, and not for additional, detailed work. There
will be rounding errors, which will accumulate if you
continue to work with the data. Data spacing in the
Geotiff image is likely to be in irrational, real units
(a function of the screen size and data spacing), and not
the simple spacing of the original data.
- If you reopen the Geotiff, it is likely that on redrawing
the UTM grid some of the grid lines will shift by a pixel
because of rounding errors. Thus some of the grid lines
will have a double width. (Turn off the grid before saving).
- If you view the Geotiff at less than the scale it was
saved at, some of the UTM grid lines will likely
- This is really the same as saving as a BMP, JPEG, or GIF
image, except that the program can associate coordinates
with each point.
- The file will be saved in uncompressed 24 bit color,
regardless of the original data format. This is required
so that overlays can be stored, and results in simpler
coding because only a single TIFF format is required.
- For optimal results if you want to do anything more than
just save a dumb map, save a 1:1
map with no grid or other overlays; you can always
regenerate the grid and overlays later.
- If you want to save for additional work at the full
resolution of the original data, you should use the
subset functions on the Data
Last revision 2/18/2008