Latest Contributions by DjordjeSpasic

‎09-09-2016

Hello, I was wondering, can somebody please answer whether the curvature analysis in ArcGIS is Gaussian or Mean curvature analysis? Which one of these two? Thank you for the reply.

‎10-16-2015

I already have the .asc file. I do not have the initial model from which attached .asc file is derived. And why would I have to make a raster from that initial model (which I do not have) and then reexport it to .asc again (which is what Raster to ASCII tool does)? Upper photo is digital terrain model created in Rhino, based on attached .asc file. The problem is: whether the cell width/height is correct or not.

‎10-16-2015

Thank you for the reply Dan. I think the misunderstanding part is than Rhino application can not express its terrain model in degrees. Only in length units: meters, feets, inches... As elevation values from .asc file are in meters, there has to be a way to convert cell's width/length from decimal degrees to meters too. This is what the upper two equations are doing.

‎10-16-2015

I appreciate the reply Dan. The table you have given me shows the lengths of a single degree of latitude and longitude depending on latitude, for WGS84 model, which depicts Earth as a modified reference ellipsoid. I am not asking for equations on how to calculate the length of a single degree of latitude, longitude depending on latitude. What I would like to do is to make a terrain model (in Rhino, not ArcGIS) from upper attached .asc file and its elevation data, by simplifying Earth as a sphere. .asc file elevation data is always in meters, so this is not a problem. The issue is: which length needs to be taken for each cell width(height) of the xy grid, when building a terrain model: Should cell width and height always be: cellWidthAndHeight = cellsize * 111120 meters regardless of the "yllcorner" value (this is the latitude of DEM's origin)? Or should the cell width and height take into account origin's latitude: cellWidthAndHeight = cellsize * 111120 meters * cos(latitude) ? (111120 meters is approximate length of 1 degree of latitude and longitude on equator, in case of simplified sphere Earth model). Thank you.

‎10-16-2015

Thank you for the reply Dan. "The cell width and height are equal..." What does this mean? That if one simplifies Earth as a sphere, the width and height of the cell will always be equal to: cellWidthAndHeight = cellsize * 111120 meters regardless of the origin's ("yllcorner") latitude? (1 degree of latitude and longitude on equator is approximately 111120 meters).

‎10-15-2015

Dear GeoNet community. I was wondering if somebody could help me with an issue related with cell width of an esri grid format (.asc file). What I would like to do is to import an elevation data from an .asc file to Rhino 5 application. In Rhino 5 I am opening an .asc file with IronPython 2.7, and then generating a terrain model from elevation values. However, there is one thing that confuses me: is the width of the cells always constant? To make it more understandable, here is a small example of how an .asc file looks like: ncols 38 # number of cells in x direction nrows 29 # number of cells in y direction xllcorner 2.140416666625 # bottom,left corner's (origin) longitude yllcorner 41.350416666671 # bottom,left corner's (origin) latitude cellsize 0.000833333333 # size of the cell in decimal degrees NODATA_value -32768 # no elevation value. 36 34 35 33 34 36 32 29 32 35 39 39 41 40 38 41 38 39 37 40 38 38 37 34 ... # elevation values I also attached that .asc file bellow. It's an elevation data for Barcelona. Here is a visual representation of upper mentioned values from .asc file taken from wikipedia (which is copied from ArcGIS help😞 I simplify the Earth model to sphere, and assume that one degree of latitude and longitude at equator is 111120 meters. Then I use the "yllcorner" variable's value (origin's latitude) to calculate the width of the cell size: cellWidthMeters = cellsize * 111120 * math.cos(yllcorner) The value of "cellWidthMeters" that I get is the width of the cell at that (yllcorner) latitude. It is also the cell height at any longitude, as this one is constant. What I do not understand is, why isn't the width of the cells changing, as the latitude is changing? Something like this: Why is it always constant? The width of the cell is in degrees of longitude at "yllcorner" latitude. So the width of the cell should be shrinking as we go further from the origin, because the degree of longitude is shrinking the larger the longitude is. Or did I get this completely wrong? Thank you for the reply. Regards, D

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Latest Contributions by DjordjeSpasic

Curvature analysis in ArcGIS

Re: Why is esri grid cell width always constant?

Re: Why is esri grid cell width always constant?

Re: Why is esri grid cell width always constant?

Re: Why is esri grid cell width always constant?

Why is esri grid cell width always constant?