21 January 2013

Version 1.1 of Snuffler Released

The latest version of my geophysics software, Snuffler,  has made an appearance. What wonders are there to be seen this time around?

The main new feature is channel merging. This is where you can display multiple plots on the same image, for example a magnetometry and resistivity plot. The one restriction is that the grid layouts of the various surveys must be on the same alignment, but apart from that, the grids needn't be the same size, shape, be in the same place, or be at the same resolution. Here is an example. The survey is of a  medieval farmstead that was in use until quite recently, and is now in a woodland, under some trees. The magnetometry is in red, and the resistivity is in green. As you can see from the top-right corner of the image, there is a high resistance feature that has a large magnetic halo around it. This is the whole point of the channel merging idea, comparing the location of features on different plots.

Also added is manual destriping. If you have areas of particularly high magnetism in your magnetometry survey, the normal destriping tool may struggle to get it right. You could always use the Modify Selection tool, but that isn't particularly fast. Now you can simply select a line to modify using Ctrl  + mouse drag, and then use the two new buttons in the toolbar to add or subtract 0.5. The selection of the line will be hidden, though not de-selected, to aid visual comparison with adjacent lines.

Finally, I wanted to speed up the screen drawing a bit, as Snuffler can be a bit sluggish at times, especially with large images. One of the things that was slowing it down was having to support the dot density plot. I was thinking of how to speed up this part of the software, when I suddenly realised, 'Why on earth would you want to use the dot density plot?'. Let me give you a bit of background on that. When archaeological geophysics first started out, computer equipment was a lot less sophisticated. Everything was in monochrome, unlike today, where you can display and print in shades of grey. A 4x4 square of pixels, with various pixels black or white, will give you 16 'shades'. This restricts you to having a single reading a minimum of 4 pixels wide, and it still wont look anywhere near as good as a proper grey scale. The dot density plot is an anachronism, and needs to go. No-one should be using it any more, so the choice to me was clear, dot density had to go. But where I taketh away, I also giveth. I had been asked if I could provide a greater number of grey shades for the display. Snuffler had supported 16 and 32 shades of grey, now there is an option for 64. When I first wrote Snuffler, 16 shades of grey was 'browser safe', i.e. you could be sure that any browser could display all the shades. I'm sure browser technology has moved on since then. Not all surveys will benefit greater from 64 shades of grey, but here is part of an image which shows that off to an extent. The graduation of colours shows up nicely in the alluvium next to the Roman port.

The difference between the 16 shades at the top and the 32 shades in the middle is obvious, but I must admit that I struggle to see much difference between the 32 shades and the 64 shades at the bottom. I am assured that some people can. On the subject of shading, I found some interesting blog posts about why colour shading is a really bad idea, but don't worry, I wont be removing those.

You can of course download the new version of Snuffler at the usual place.


  1. Hi David - this is great, many thanks for the continued support of this vital piece of software. I use it regularly for creating data from our RM85 and 601-2 machines. I wondered if you might consider doing a blog post on the mechanics of importing into Snuffler, the meaning of the 0,0 origin, the differences between 'top left' and 'bottom left' imports and the relation of the Snuffler grid orientation to the survey orientation. Although I am a regular user, I still don't think I fully understand the import process and sometimes doubt my output until I see a feature of which I know the orientation of. Thanks again, Matt.

  2. Matt, I'm glad to hear the software is useful. You are the first person to say they are using it with the new RM85. Do you just use the RM15 option for import, without any issues?

    As for the 0,0 and top-left or bottom-left. It's all linked to mathematicians. They tend to think like a graph, where the x and y axis are in the bottom left corner and increase in value to the top and right, whereas a lot of people, me included, think of position x = 0, y = 0 in the top-left corner of the image, increasing in value to the bottom and right. The option to choose between these in the XYZ import will allow you to process data output from software that may differ to Snuffler in it's view of where 0,0 should be, so while Snuffler thinks 0,0 is in the top-left corner, Geoplot thinks it is in the bottom-left. If you didn't tell it the right way on import, your imported data could be upside down. I hope that makes sense.

    1. That's great, thanks for the quick reply David. Yes, we haven't had any issues importing the RM85 data using Snuffler with the RM15 option.

      So what you are saying is that I should always use the top right option when using Snuffler? The reason I ask is because I have some data which I did this with and it came out the wrong way, when I used bottom right it was okay.

      How does the import related to say a grid surveyed using the Bartington, because I can in theory survey it starting at any corner, as long as I go clockwise - and does Snuffler care about the start direction I enter into the Grad at configuration?

      Thanks again, Matt.

    2. Ah, I think you are talking about something different. My previous reply, and the 0,0 stuff applies only to the XYZ import. Are you talking about importing direct from the machine? With that, decide which end of your survey area, usually north, is going to be towards the top of your image. You then work out in which corner of the grid you would have started in relation to that, so for instance, if north is to the top of the image and you started in the north-east corner of each grid, then you would select the top-right corner, south-west corner would be bottom-left, etc. You can decide whichever corner you want. The effect would be the grid layout in the map would be different, and the final image would be rotated accordingly.

  3. The comment is not related to the article, but I want to ask you!
    I downloaded the Snuffler, but I can not use certain options. Why is that?
    I can not use these functions: Modify seletion, interpolate, despike, remove geology, edge correction, destribe, clip data, destagger.

    1. Are you trying this in a preview? Data can't be modified in a preview, only a view.

    2. Thank you very much for your answer, this was indeed the problem. I clicked the wrong place!
      The Help I can not open it. Why is that?
      Anyway, the program is very good!

    3. The help should be accessible from the help menu. Does it not load correctly? What version of windows are you using? The help file is installed in the same place as the software, with a file extension of chm. If loading that from the directory doesn't work, then the problem is your OS. If you can, then it is me doing something wrong.

  4. Hi David. Have been using Snuffler for some time. Occasionally have a problem with View when I try to display Grid lines. It sometimes splits the grid into 4 rectangles. Usually happens with large grids.
    Solution seems to be open new View of map.
    Is this a known bug?
    Regards Fred

  5. It isn't a known bug, so I would be interested in knowing what steps are necessary to reproduce it. No need to open a new view, the grids can be corrected using Display Settings > Grid Settings.