Dear all,
I have an unexpected problem:
The results after terrain analysis shows empty cells (indicated as white points, distance about 125 m; see image 1+2); in case of e.g. convergence between these empty cells reduced values (see image 3);
Elevation 55 m ; nearly 2000000 records;
Procedure: From .txt > ArcGIS > shape file load in SAGAgui 9.02 > terrain analysis;
The original file is free of theses empty cells.
Isn't there a step missing from the procedure? I assume we are talking about the "Basic Terrain Analysis" tool from the "Compound Analysis" library?
The input for the tool is a grid. Your described procedure says:
shape file load in SAGAgui 9.02 > terrain analysis
What is the process from the shape file to the grid dataset? From your previous post I know that you are not interested in creating the dataset from .txt with SAGA and taking an interpolation into account. It seems you have now made the step from .txt to shape file with ArcGIS. Why don't you also convert the shapefile into a grid in ArcGIS?
The original file is free of these empty cells.
Which file is meant here? The shapefile or the raster dataset?
Last edit: Justus Spitzmüller 2023-10-30
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Dear Justus
(i) In the attachment a step by step description what I did.
(ii) SAGA and taking an interpolation into account. It seems you have now made the step from .txt to shape file with ArcGIS. Why don't you also convert the shapefile into a grid in ArcGIS?
Until now I load only shp-files (created in ArcGIS) in SAGA, and had no problems with zhis confusing images
(iii)
The original file is free of these empty cells.
Which file is meant here? The shapefile or the raster dataset?
That means the shpape-file from ArcGIS is free of theses empty cells.
Kurt
Could you please overlay your point shapes on top of the slope map, zoom to an area with an empty cell and take a screenshot?
I would be interested to see the location of your points in relation to the raster cells. Seems to me like these do not match (causing the artifacts you observe).
Best regards,
Volker
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Thanks for the illustration. The pattern (I believe) I see is that the empty cells have all four points at the nodes. Leaving no Point within the cell.
Since your 5x5 shape follows a regular(ish) distribution, but it is not orthogonal and thus the suggestion Shapes to Grid leads to strong artefacts. I would suggest either interpolate or do the grid creation outside of SAGA.
(But keep in mind, rectangular grids are a key design element from SAGA)
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As Justus wrote, these data gaps are introduced because sometimes none of your points are located within a grid cell. The other artifacts come from the same problem: your points do not represent a regular grid. There are several ways to work around this, including interpolation.
But the first question should be: why is your point data like this? It seems like the points are created from an elevation model (most likely a raster) and are now slightly rotated. Instead of trying to work around the problem, I would try to fix the input data. How did you create these points? And if the original data source was a raster elevation model, why do you convert it to points in the first place?
Best regards,
Volker
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Dear all,
I have an unexpected problem:
The results after terrain analysis shows empty cells (indicated as white points, distance about 125 m; see image 1+2); in case of e.g. convergence between these empty cells reduced values (see image 3);
Elevation 55 m ; nearly 2000000 records;
Procedure: From .txt > ArcGIS > shape file load in SAGAgui 9.02 > terrain analysis;
The original file is free of theses empty cells.
How can I avoid these problems?
Thank you
Kurt
Isn't there a step missing from the procedure? I assume we are talking about the "Basic Terrain Analysis" tool from the "Compound Analysis" library?
The input for the tool is a grid. Your described procedure says:
What is the process from the shape file to the grid dataset? From your previous post I know that you are not interested in creating the dataset from
.txtwith SAGA and taking an interpolation into account. It seems you have now made the step from.txtto shape file with ArcGIS. Why don't you also convert the shapefile into a grid in ArcGIS?Which file is meant here? The shapefile or the raster dataset?
Last edit: Justus Spitzmüller 2023-10-30
Dear Justus
(i) In the attachment a step by step description what I did.
(ii) SAGA and taking an interpolation into account. It seems you have now made the step from .txt to shape file with ArcGIS. Why don't you also convert the shapefile into a grid in ArcGIS?
Until now I load only shp-files (created in ArcGIS) in SAGA, and had no problems with zhis confusing images
(iii)
The original file is free of these empty cells.
Which file is meant here? The shapefile or the raster dataset?
That means the shpape-file from ArcGIS is free of theses empty cells.
Kurt
Could you please overlay your point shapes on top of the slope map, zoom to an area with an empty cell and take a screenshot?
I would be interested to see the location of your points in relation to the raster cells. Seems to me like these do not match (causing the artifacts you observe).
Best regards,
Volker
Dear Volker,
under point 5 are the overlays.
Thanks
Kurt
Thanks for the illustration. The pattern (I believe) I see is that the empty cells have all four points at the nodes. Leaving no Point within the cell.
Since your 5x5 shape follows a regular(ish) distribution, but it is not orthogonal and thus the suggestion Shapes to Grid leads to strong artefacts. I would suggest either interpolate or do the grid creation outside of SAGA.
(But keep in mind, rectangular grids are a key design element from SAGA)
As Justus wrote, these data gaps are introduced because sometimes none of your points are located within a grid cell. The other artifacts come from the same problem: your points do not represent a regular grid. There are several ways to work around this, including interpolation.
But the first question should be: why is your point data like this? It seems like the points are created from an elevation model (most likely a raster) and are now slightly rotated. Instead of trying to work around the problem, I would try to fix the input data. How did you create these points? And if the original data source was a raster elevation model, why do you convert it to points in the first place?
Best regards,
Volker