Long execution time, low CPU

kevineckkevineck Global Mapper UserPosts: 2
edited January 2008 in Technical Support
I am using Global Mapper to geo-reference a large number of hand drawn (but to scale) maps. Images are PNGs and can range in size from several hundred megs to about a gig or so. My workflow involves several iterations of re-rectifying to achieve the results I am looking for. I may start with 4-5 GCPs and end up with 15-20 for a large irregularly shaped map. Due to the size of the image files and the number of GCPs I'm not surprised at the long execution times, but when looking at Global Mapper in Task Manager it shows that it is only using in the low 10's of megabytes of memory and CPU utilization is only 0-2%. I've tried increasing the process priority and sometimes I'll see CPU utilization jump up into the 30-50% range for a moment or two, but it then settles back down to almost nothing. I notice this most often when opening and using the rectification window and applying the changes once the image has been rectified once. I also notice this when changing which layers are visible and one or more of them is a rectified image. Should the CPU utilization be that low? I would guess that the calculations to rectify the image with a large number of GCPs would be pretty CPU intensive, which is why I was puzzled to see it take a long time with low cpu utilization. Is there some other bottleneck I should look into that might speed things up a little?

I'm running Global Mapper 9.01 using Windows XP on a 2.13 ghz Core 2 Duo 6400 with 2 gigs ram.

Thanks for any suggestions!

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited January 2008
    I actually think that most of the execution time is actually disk access. When you open a large PNG file it is decompressed to disk to avoid using a ton of memory since you can't randomly access data directly from a PNG file. So whenever the image is rendered the disk drive where it was decompressed to (this would be the one containing your TEMP folder) is hit to access the data. Disk access is very slow compared to memory access so not much CPU is used, but it takes a while.

    One thing I can think of to make this faster is if you converted your PNG files to TIFF files, likely using LZW compression if possible. TIFF files support random-access and the caching mechanisms are more efficient, resulting in better performance for very large files.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • kevineckkevineck Global Mapper User Posts: 2
    edited January 2008
    Thanks for the information about TIFFs and PNGs. You learn something new every day. Funnily enough I've actually been converting from TIFF to PNG prior to the rectification process since many of the images are irregularly shaped and I want a transparent PNG as my final output. I'll try using the TIFFs first and making the conversion to PNG later.

    On a related note, how do the image manipulation/conversion routines in Global Mapper compare to those in Photoshop? Specifically, would it be better to export directly to a PNG from Global Mapper or export as a TIFF and and make the conversion in Photoshop? I need to open the rectified images inside Photoshop anyway so performing the conversion there doesn't add to the workflow significantly.

    Thanks again for the suggestions and the quick reply.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited January 2008
    Both the PNG and TIFF formats are lossless, so you should get the same results wherever you do the conversion. So I would recommend whichever is most convenient for you.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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