Combine elevation data

VincentR

I need to combine two elevation layers (sounding grids):

- one larger area which contains older data (Old Layer)

- one smaller area which contains updated data (New Layer)

The combined layer has to contain the New Layer and Old Layer for the locations where the New Layer has no information / is not valid. (In other words, the large area, cropped by and updated with the latest sound grid).

With the operations in the Combine/Compare Terrain Layers, I can't figure out how to achieve this. Any suggestions?

(and if there would be an alternative route using points rather than grids, that is also an option for me).

sphillips

I struggled to understand the Combine/Compare Terrain function so made this visual guide years ago. Hopefully it will make it easier to understand than their description.

You can also physically place them on different layers and feather the edges of the uppermost layers to blend the edges seamlessly. Then export out as a new dataset.

BillB

Thanks so much for sharing - that could be a great reference going forwards.  Should perhaps be part of the Global Mapper manual, Blue Marble!

VincentR

Thank you, @sphillips ! That is a very clear presentation of the Combine/Compare terrain options, very insightful!!!

With your overview of the operations it is quite clear that what I need is not included in the options for v21.1.

I took some markers and drew the update/replace operation similar as you presented in your visual guide (the result is however not as neat as yours )

The top drawing is the original separate layers A and B.
The second is the combined layer where A replaces B.
The third is the combined layer where B replaces A.

At the bottom three models in topview:

• Left are the individual layers before combining.
  
• Middle is the combined layer where A replaces B
• Right is the combined layer where B replaces A

In words: A updates/replaces the values in B. If there is no value for A, value of B will be used.

When working with bathymetry, this is a very common operation to perform, e.g. when surveys are executed on different dates.

An update/replace layer operation would be a very welcome addition for me to the Combine / Compare layer options.

sphillips

BillB said:

Thanks so much for sharing - that could be a great reference going forwards.  Should perhaps be part of the Global Mapper manual, Blue Marble!

No problem at all. I wish there was a graphical explanation in the guide as the description isn't intuitive to me at all. No one in work was able to make sense of it; hence my attempt to explain it in a guide.

This hasn't been reviewed by anyone so there is potential for errors. If anyone see any issues please let me know so I can update.

sphillips

VincentR said:

Thank you, @sphillips ! That is a very clear presentation of the Combine/Compare terrain options, very insightful!!!

With your overview of the operations it is quite clear that what I need is not included in the options for v21.1.

I took some markers and drew the update/replace operation similar as you presented in your visual guide (the result is however not as neat as yours )

The top drawing is the original separate layers A and B.
The second is the combined layer where A replaces B.
The third is the combined layer where B replaces A.

At the bottom three models in topview:

• Left are the individual layers before combining.
  
• Middle is the combined layer where A replaces B
• Right is the combined layer where B replaces A

In words: A updates/replaces the values in B. If there is no value for A, value of B will be used.

When working with bathymetry, this is a very common operation to perform, e.g. when surveys are executed on different dates.

An update/replace layer operation would be a very welcome addition for me to the Combine / Compare layer options.

Do you have any sample data to test (or zip a GMP)? Can you just load the layers and place B above A (or vice versus as required)? Then export them to a new dataset?

VincentR

Yes, that does the trick! (=>Load and order the layers and export to a new dataset).

Never would have thought of that route, thanks for pointing in the right direction, @sphillips !

(..and I was a bit too quick clicking the question was not yet answered, which now it is...)