Are there any tools that can take a DTM, in asc or geotiff format and generate a mesh from this that can used in meshlab or similar software.
I have asc DTM file that I need to convert to a ply mesh file. Is this possible?
In response to the comment. Then these DTM asc files are not the ones that meshlab understands.
The files starts with:
ncols 6250
nrows 6250
xllcorner 630000.000000000000
yllcorner 6070000.000000000000
cellsize 1.600000000000
NODATA_value -9999
A DTM raster can be represented by triangle meshes by finding a set of non-overlapping triangles that covers the entire mesh and approximates the elevation field. There are two different types of triangle meshes that can be used for this purpose:
In most applications, if you need to deal with elevation meshes, you'd go with a TIN since throwing out redundant or nearly redundant information allows for more efficient computations. However, creating TINs from rasters isn't straightforward, since there are many different triangulations that approximate a grid with the same error, but using different vertex sets.
Software for creating TINs
Raster to TIN function from the 3D Analyst toolbox.Grid to TIN (Surface Specific Points) function, followed by Export TIN to Stereo Lithography File (STL) function to export the TIN to a mesh format readable by Meshlab.Software for creating TRNs
Grid to TIN function.Roll your own solution: Implementing it isn't particularly hard. Here's a Python script that uses the GDAL library to read a raster DTM, and then writes out a binary PLY mesh.
Save the script as gdal_rastertotrn.py, then call it using python gdal_rastertotrn.py <inputraster> <outputply>.
Here's an example. Converting a raster DTM of Crater Lake called crater_lake.tif...
... by calling python gdal_rastertotrn.py crater_lake.tif crater_lake.ply, and opening the resulting crater_lake.ply in Meshlab:
Here's the (unpolished) script. Since it uses the GDAL library, it can convert all raster types supported by GDAL. It only writes PLY files.
#!/usr/bin/python
import sys
import numpy as np
from osgeo import gdal
def write_ply(filename, coordinates, triangles, binary=True):
template = "ply\n"
if binary:
template += "format binary_" + sys.byteorder + "_endian 1.0\n"
else:
template += "format ascii 1.0\n"
template += """element vertex {nvertices:n}
property float x
property float y
property float z
element face {nfaces:n}
property list int int vertex_index
end_header
"""
context = {
"nvertices": len(coordinates),
"nfaces": len(triangles)
}
if binary:
with open(filename,'wb') as outfile:
outfile.write(template.format(**context))
coordinates = np.array(coordinates, dtype="float32")
coordinates.tofile(outfile)
triangles = np.hstack((np.ones([len(triangles),1], dtype="int") * 3,
triangles))
triangles = np.array(triangles, dtype="int32")
triangles.tofile(outfile)
else:
with open(filename,'w') as outfile:
outfile.write(template.format(**context))
np.savetxt(outfile, coordinates, fmt="%.3f")
np.savetxt(outfile, triangles, fmt="3 %i %i %i")
def readraster(filename):
raster = gdal.Open(filename)
return raster
def createvertexarray(raster):
transform = raster.GetGeoTransform()
width = raster.RasterXSize
height = raster.RasterYSize
x = np.arange(0, width) * transform[1] + transform[0]
y = np.arange(0, height) * transform[5] + transform[3]
xx, yy = np.meshgrid(x, y)
zz = raster.ReadAsArray()
vertices = np.vstack((xx,yy,zz)).reshape([3, -1]).transpose()
return vertices
def createindexarray(raster):
width = raster.RasterXSize
height = raster.RasterYSize
ai = np.arange(0, width - 1)
aj = np.arange(0, height - 1)
aii, ajj = np.meshgrid(ai, aj)
a = aii + ajj * width
a = a.flatten()
tria = np.vstack((a, a + width, a + width + 1, a, a + width + 1, a + 1))
tria = np.transpose(tria).reshape([-1, 3])
return tria
def main(argv):
inputfile = argv[0]
outputfile = argv[1]
raster = readraster(inputfile)
vertices = createvertexarray(raster)
triangles = createindexarray(raster)
write_ply(outputfile, vertices, triangles, binary=True)
if __name__ == "__main__":
main(sys.argv[1:])
We have just created an open source project that will help you do exactly what you want. Tin-Terrain is a simple command line tool that will generate a mesh from DEM files either as TIN or TRN.
The output can be saved as .obj file, so can be directly drag-and-dropped into meshlab. It will also support tiling with zoom levels in quantised mesh format.
