Resolve issue where the Vertical Mapper Region Inspection calculates Mean Value higher than the Max Value for certain regions

Product Feature: Region calculation

 

Issue

A customer has come across some strange results while using Region Inspection in Vertical Mapper. 
After running a region inspection on a layer that has a couple of polygons, the Mean Value is higher than the Max Value. 
 
This issue does not arise in all polygons, only in some of them. 

Cause

Here is what is wrong, and I will explain you with the example of a region which is having the wrong information. 

The region which I am considering is the triangle which has the following bounds: 

X1: 495345.67 Y1: 6615765.60 
X2: 498413.52 Y2: 6618064.62 

Here when we do the analysis, we figure out the following: 

Total Number of Cells(Partial coverage and full coverage) under the region: 54 
Number of Partial Cells under the regions: 16 
Number of Full Cells under the region: 38 

Now in the case of the region that we are considering, while calculating the sum, we are considering all the 54 cells. 
But when we are calculating the mean, we are dividing the sum/46. This is because 38 cells are complete + 50% of partial cells (which is 8). 
So the cell sum is for all 54 cells, but we are dividing by a lesser number and therefore we are getting values which are higher than the Zmax. 

If you change the registry entry to have a decimal value of 100, you will notice that the mean falls within the range of Zmin to Zmax. This is because 
in that case we will be dividing the sum by 54 which is the total cells. 

So this is a bug in VM, VM-199

Resolution

UPDATED: September 8, 2017
With VM 3.5, we had introduced the concept of Partial Pixel Weight. 
This meant that we give a uniform weight for all cells that are just partially covered under the region. 
This value is configurable using a registry entry: 

HKEY_CURRENT_USER\Software\MapInfo\MapInfo\Vertical Mapper\370 

DWORD Key: PartialPixelWt 

If undefined in the registry, the default value for this entry is 50%. 

RESOLUTION
  • Open the Windows Registry
  • Browse to HKEY_CURRENT_USER\Software\MapInfo\MapInfo\Vertical Mapper\370
  • Right click > New
  • Create a DWORD key with the name PartialPixelWt like in the screen shot below:
            User-added image
  • Restart MapInfo and Vertical Mapper