Global Mapper v25.0

Merge multiple ECW files -

STH
STH Global Mapper UserTrusted User
edited October 2007 in Technical Support
What is the easiest way to merge multiple overlapping ECW-files?
I have one large (5GBB) and several smaller ones (50mb each). I need to merge these into one large. In GlobalMapper they are shwon fine, but the white areas around the map tiles are shown. If I go to each ECW-file and set transparent background to 255-255-255 (white) it does not work. I guess this is because an ECW- file does not have background-color as a regular file (Tiff/JPEG etc).

I do have the areas described in vector data, but how can I set the vector-file (DXF) to be the "clipping area" for the top-most layer and everything outside is transparent so the maps on the layers below the top-most will get drawn?

So far I have to say I`m impressed with all possibilities to import/export both vector and rasterfiles.

Thanks for your fast reply. If it works well I hope to perhaps write some tutorials.

Comments

  • global_mapper
    global_mapper Administrator
    edited October 2007
    For lossy formats like ECW the collars are often several colors near white or black. Here is the solution for removing those collars (this is from the Global Mapper FAQ):

    Question: How do I remove the collar from overlapping imagery files?

    Answer:
    If the collar surrounding your imagery files is either black or white (or very close to one of those colors), you can use either the Darken or Lighten blend mode functionality in Global Mapper to remove the collars. To setup the blend modes, open the Control Center (found on the toolbar and under the Tools menu), highlight the imagery layers that you want to remove the collar from, and select the Options button. If the color is black, select the Lighten blend mode from the Blend Mode drop-down list. If the collar color is white, select the Darken blend mode. Then press OK. Finally, you'll also need to set the background color of the Global Mapper view to be either black or white to match the collar color so that the non-overlapping regions aren't affected. You can change the background color under the View menu.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • STH
    STH Global Mapper User Trusted User
    edited October 2007
    I knew I saw something about it, but thought it was on the forum,I`m sorry.

    It works. However I have another problem. If you think of the largest ECW-file as a square area it ranges from far north/west to far southeast so actually only around 10-20% of the area is actually filled with photos. Changing the background layer to for instance yellow shows that all the background is correctly labeled. However is there any other way of speeding up the creation of the ECW file? Somehow mark that the background can be set to white-ish and just process the remaining parts? (I`m not very familiar with the structure and algorithm of ECW - sorry.)

    I have now processed for 10 hours, and its 1% complete. Unfortunately there is no progress bar - but experience from using ERMapper shows that it does take a long time to generate ECW files and the time does not decrease after for instance 2 days.

    Estimated time with ERMapper for the same file is around 10-12 days.
  • global_mapper
    global_mapper Administrator
    edited October 2007
    Unfortunately there really isn't any quick way to identify background pixels from ECW files without actually decoding them first. It sounds like you must be generating a HUGE ECW file that the progress bar is going so slow. I guess 5GB is massive for an ECW file.

    I think what will slow you down in this case is that each row of the ECW file has so many pixels in it that the cache of ECW tiles along a row is not large enough to hold enough tiles to fill the row, meaning that the subsequent exported row has to re-fetch the ECW files all over again. What you could do to speed this up is to use the Gridding tab when exporting to break your export up into smaller pieces so that the internal cache can actually be useful, which would speed things up tremendously. Of course you would end up with a collection of smaller ECW files rather than a single large one.

    Another approach if most of the data is background would be to draw an area feature around the areas that actually have data, then select the area feature(s) with the Digitizer Tool, then do your export cropped to the selected area feature(s) (there is an option for this on the Export Bounds tab of the Configuration dialog). For any samples outside the area feature(s), the ECW file would not be queried at all, which would improve cache usage and perhaps significantly speed things up if enough of the image is just background.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com