Shifting the start-point for a measurement - Measure across a crack

Last update 18 Mach 2018

A trick for CDendro users:

Sometimes I want to continue measuring from a new point, like this:

Here, this is done when going from point 58:1 to 58:2 on the same ring. Then I register point 58:1 and 58:2 as a  group.

So before clicking on point 58:1, I click on the datagroup button to change the mode from a-single-point-per-row.
You can also use the right mouse button to change this mode!.

Then I click on point 58:1 and 58:2.
The group mode will switch back automatically to single point mode when data is known to be dendro data!

The written data will look like this:

18.655,16.210  15.226,7.940

I.e. with the two points 58:1 and 58:2 on the same line.

CDendro is set up to handle this type of grouped data. This is a very useful method when you have to make a jump in your measurements when ring widths are laying aslant on the picture.

Of course, if tree rings are not very concentrical you have to be careful when interpreting your data if you have moved your radii of measument within the stem!

Measuring across a crack

When measuring across a crack you might use the method described above. Though when setting the point 25:1 above you have to compensate for the width of the crack to make the distance between point 24 and 25:1 correspond to the actual width of the broken ring.

Using the CrackMarker tool when measuring over a crack

There is a tool in CooRecorder to measure across a crack - the CrackMarker tool.

The picture above shows two possible paths for measuring across the crack. The upper path is very precise and it is the method to be prefered when possible, i.e. the old way as described above with a pair of measuring points.

Though there are cases when you cannot traverse the crack that easy. Then the lower path may be considered!

When using the CrackMarker tool you can set a crackmark point at each side of the crack as shown above. When CDendro reads the .pos file, it will subtract the width of the crack from the full width of the ring.

The main problem with this method is that it is difficult to see the edges of the crack as the scanner does not look in right angles towards the wood surface. Instead this picture was obviously taken aslant, as it shows a bit of the inside of that crack as a light area.

To use the CrackMarker tool, click on its button and it will light up. You can also select it with the M key on your keyboard. Then click where you want to set the points. When ready, click e.g. the D key (data mode) to continue measuring as normal.

You may set a single crackmark in front of a ring border as shown above. You may do so also in front of a W-point at a latewood/earlywood border. There is no limit for the number of crackmarks within the same ring but they have to be on a straight line to make the measurements correct - see the tooltip in the following image (from CooR version 9.3)!

Note: Very old versions of CDendro will ignore all crackmarker points.

Note: There has been a report on CDendro ignoring %gap  %gap markers when having set Windows to
1. running with decimal separator set to a comma (,) and
2. with Polish selected as the region.

The error can be circumvented by changing the decimal separator in Windows to a dot (.), though this might have side effects on other software and old data. The error has been fixed in the TEST version of CDendro 7.5 from 2 November 2011.

Extensive use of start-point shifting

Here is an example of a sample that has been heavily eaten up by the house longhorn beetle. The trunc is in the Sandviken house at Västanvik, Nämdö and was sampled by Lars Löfstrand in 1994.

The picture demonstrates how you can again and again shift the starting point when measuring a next ring width.

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