7 replies to this topic

[jt83]

Not technically a CF query so if this needs moving - all well and good.

I'm dealing wtih some lidar taken close to the ocean, so that when it's imported into Global Mapper it looks like -

 

Looks OK.  In Wilbur the .bt file appears as -

 

Purple bits are a bit funny, confirmed when the PNG surface appears as this in Photoshop -

 

Obviously not suitable to finish the job.  In Wilbur there's also a strange negative value in Map Info -

 

I've PMd Joe H but he's been inactive for a week.  Would appreciate any ideas.

[Larrykuh]

In my experience, almost every lidar I process has the negative -32768 value for the minimum. Not sure why. What I do is replace the negative value with the minimum you get from Global Mapper. In Wilbur, from the menu select "Filter->Fill-> Replace". Then set "Base Value" to -32768 and "New Va;ue" to the minimum you wrote down from Global Mapper. In the case of lidar near the ocean, you should probably set the "New Value" to zero if it is less than the Global Mapper minimum.

[Brucey Mc]

Yes setting the min value to zero works nicely I have done that q few times

[jt83]

In my experience, almost every lidar I process has the negative -32768 value for the minimum. Not sure why. What I do is replace the negative value with the minimum you get from Global Mapper. In Wilbur, from the menu select "Filter->Fill-> Replace". Then set "Base Value" to -32768 and "New Va;ue" to the minimum you wrote down from Global Mapper. In the case of lidar near the ocean, you should probably set the "New Value" to zero if it is less than the Global Mapper minimum.

 

Seemed to do the trick Larry.  The Global Mapper max/min was 55/-1; when I set the base value to -32768 and left the new value at zero in Wilbur, then clicked map info, it showed up as exactly 55/-1.

Questions - if I'd put -1 as the new value, would that have thrown anything off?

In Joe's tutorial, the Unity height is the difference between the max and min values.  So if the max is 55, the min is -1, is the correct height 56?  Possibly being a bit pedantic here...

[Larrykuh]

I set the minimum in wilbur the the lowest value. In your case, I would have set it ot -1. It doesn't matter that much as Wilbur did get the min of -1. Yes, for Unity, it is the difference of the min and max, so adding the negative to the max was correct.

[jt83]

Larry something else has popped up.  I have some lidar that had a max/min of 55/-0.7 in GM.  When I checked the max/min in Wilbur, the max was 25.8 (min -32768).  Any idea why the disparity?

I thought it might have something to do with the 2048 grid in GM...like maybe the GM figures were being read when I had the grid selected/deselected, so I tried getting the max/min with the grid on and off...only to get the same numbers.  Does that mean when you have a large lidar area loaded in GM, the max/min is being read in areas outside the grid, therefore not being the right numbers for the Unity map?

[Larrykuh]

I've never had that happen, so not sure what to tell you. Maybe Joe can chime in. You do not have to keep your grids to 2048 or 2000. The grid can be any reasonable size as long as it is a square. In GM, try to size the grid so you have 200 yards or so from your course to the sides of the grid. This should ive you ample room to hide the edges of the course with trees, etc. in Unity

[jt83]

I think I was on the right track.  When you click 'find extreme max/min elevation' in GM under Layer, it will find the max/min over the entire loaded terrain.  When you have a 2048 grid, you have to right click on it, go to Analysis/Measurement > Calculate Elevation.  That's why the large gap, there was obviously some much higher terrain in GM outside the rectangular grid.  Not a bad thing to learn.