Global Mapper v25.0

No Buffer around Areas in Islands during Roughness creation

HendrikNoecker
HendrikNoecker Global Mapper User
edited September 2013 in Technical Support
Hello Global Mapper Team,

first of all: thank you Mike for the creation of a "new build version" after my last question.


Unfortunately there are still some issues that I want to tell you (perhaps they might go on the to-do-list):

In Februray 2011 "solarwind" already mentioned the problem of missing buffers around areas that are within an island during the creation of an roughness map:
"Okay, just a note for a small issue.
When selecting all the features at step 3 to create buffers, buffers are not created for island polygons.
In fact, they are created for islands but the opposite buffer of the surrounding polygon is not created. Thus, these buffered polygons consists of one line instead of 2 lines areas. It might concern only my shapefiles because of the overlapping polygons : selecting islands is possible, but selecting the polygon underneath will select all the area, ignoring the island »» no buffer.
So, not having buffers around some polygons will lead to roughness values inconsistancy in wasp. Not sure I am clear."
Unfortunatley this issue still remains.
Here is an example of the northern part of Hamburg city, germany:

Corine Original Data (the RED is all urban area, the BLUE in the south the river Elbe and in the middel some cementry island area which cause trouble)

Hamburg corinet.PNG


The Result of the creation of the roughness areas (everything is fine so far):


Result Corine.PNG


The result of the export (Zoomed in to see the "missing" buffer of the middle green Isalnd in the center of the imagine above):

Zoom and missing Lines.PNG


I think that I can't do anything, this issue has something to to with the internal Global Mapper export routine, doesn't it?
Or is there any way to create the missing buffer so thet both roughness values are correct?

Now:
The urban area (Original RED, after creation: LIGHT GREEN) has an inner roughness value of 0.6 and an outer value of 0

Rough_L 0
Rough_R 0.6

The island (After creation: MIDDLE GREEN) has an inner value of 0.4 BUT also an outer value of 0

Rough_L 0
Rough_R 0.4


So there will be mistakes in further calculation because these 2 values doesn't correspind to each other.

Kind regards,
Hendrik.

Comments

  • global_mapper
    global_mapper Administrator
    edited September 2013
    Hendrik,

    Is the problem that the ROUGH_L of the urban area should be 0.4 and of the island should be 0.6 and they are set to 0.0? The problem is that the island isn't in any way associated with the larger parent area. The parent has a hole in it, then there is a completely different area that happens to sit in that hole. The ROUGH_L of 0.0 should only exist in a very small sliver between the areas though, does that tiny sliver just a few meters across with a different roughness significantly affect anything?

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • HendrikNoecker
    HendrikNoecker Global Mapper User
    edited September 2013
    Hello Mike,

    you are right, the tiny sliver does not really affect the further calculations. This solution with the buffers set to "-3m" is are good way to handele it.
    The problem is, that these island inside of another island (or a kind of hole inside an island) do not have a second buffer around them. They just have a Rough_L and Rough_R value.
    The Rough_R value inside of this hole is correct, but the outer Rough_L correspond to the "background value" of "0" and not to the value of the parent island.

    I can imagine that dealing with this can be quite hard, because I think that these holes inside of an area are defined in another way in Global Mapper. But adding an Buffer to this holes (like Global Mapper does to all the other areas) would be great. Otherwise in the next steps in calculations in WAsP there will be mistakes because of the inconsistensy.

    Thank you again,
    Have a nice weekend!
    Hendrik

    colors_WAsP.PNG