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Newby needs help exporting a PNG image


To start, I'm  -very-  new to Global Mapper.

I'm attempting to do what I think of as my 'Hello World' and I can't seem to make any progress.  My goal is to do everything I need by script.  Since I'm new, I'm starting my exercise by using the screen controls until I'm familiar with what they do.  Once comfortable, I'll pursue the same thing by writing a script.

Under 'Online Sources', I'm loading 'World Topo Map' with the latitude/longitude bounds set to:

   W: -119.0     S: 36.0
   E: -117.0      N: 38.0

OK so far.  From this point, I want to zoom-in and then write a simple PNG file at a specific scale that
matches what I'm seeing on the screen.

I go to:

   View  ->  Zoom View  ->  Zoom to Scale

And enter 500000 for the scale.

I would then like to write the resulting image to disk as a PNG file that I can paste into a document.

I realize I can accomplish this with:

   File  ->  Capture Screen Contents to Image

but I can't see how this would be done by scripting, so I can't use that approach (unless it is available
in the script language - but if so, I can't find it).

To get my image, I've tried:

   Export  ->  Export Raster/Image Format

I selected PNG as the format.

On the next modal I went with the existing settings, except I deselected 'Generate World File' and 'Generate Project File'

I pressed 'OK' and then gave the desired file name followed by another 'OK'.

I get a message that begins:

   The requested export will require a large number of data
   tiles to be downloaded from online sources. ...

I hit OK and as warned, Global Mapper seems to hang.

At this point I have two questions to help get me past my own hang:

- How would you export to a simple PNG file without using the 'Capture to Screen'
  feature while giving a similar result?

- Given that I need to do this using a script, would the export be the same or
  would I need to do something different?

I've been on this for several days.  I have been reading the Global Mapper documentation, experimenting
and searching the forum without any luck.  I've got to be missing something simple, but I haven't been
able to figure it out.  Can you give me any clues on how to proceed?

On second thought, I have a third question: Given an area that's only a couple of degrees on a side, why
would that require a large number tiles?

Any help/clues you can give would really be appreciated.

Thanks in advance



Best Answer

  • MykleMykle Global Mapper User Posts: 452
    Answer ✓
    In the PNG Export Options dialog, the default sample spacing is 0.29858 meters for X- and Y-.
    These represent the maximum resolution that is available from this on-line data set. 
    If you really want the maximum resolution for a large area, and are willing to wait for it, fine.
    Usually, less resolution will be acceptable for your purpose, and the file size will be manageable. 

    Experience will be useful while choosing appropriate values.  USGS 7.5' Topo maps at 2 meter sampling is somewhat of a standard.  Your area covers an extent similar to 1:250,000 1x2 topo maps which are frequently scanned at 8 meter sampling. 

    You might start with something like 8 meters for X- and Y-, and if you need better resolution then reduce the values until your results are acceptable. 

    VERY IMPORTANT: Note the Export Bounds tab on this dialog.  A useful value for on-line data is "All Data Visible On Screen".  The "All Loaded Data" option may be default, and that usually means the ENTIRE world-wide data set.  Not gonna happen.  While this setting would have been enough to stop your export, this discussion should cover other relevant details and give you something to work with. 

    If you need a georeferenced PNG, the World and/or Projection files are likely to be needed.  The PNG does not include scaling data. 



Answers

  • JHallJHall Posts: 12
    Hi Mykle,

    Thank you for your explanation.  I didn't appreciate the significance of the sample spacing.  With your explanation, I feel like I'm making progress again.

    Once again, thanks

        John

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