[GIS] How to get long, lat and altitude info from geotiff file using GDAL and C++

cgdalgeotiff-tiff

I need to get longitude, latitude and altitude info for each pixel in GeoTiff image. I have installed GDAL in my system. Since I am new to GDAL I don't know how to proceed further.

How can I get the information that I need using GDAL and C++?

Best Answer

I'm not sure what you mean by "for each pixel". look at the raster API tutorial: http://gdal.org/gdal_tutorial.html. specifically look at the section "Getting Dataset Information".

do you want to get the information that gets dumped by the gdalinfo tool? that is easy. the gdalinfo tool source code comes-with the source download. just get it and look at it. very easy to understand.

Now I see the "altitude" part. Duh.

The raster (pixels) are numbers which are the altitudes. if you know the pixel row/col, it is relatively easy to get the lat/lon/alt. look at the source for gdallocationinfo. it will show you how to take coordinates and look up the pixel. You'd do the same thing, but you don't need to convert from coordinates to pixel since you're starting with pixel coordinate. then you want to convert the pixel to coordinates in some SRS. look at gdaltransform for that.

Also the tutorials. The raster API tutorial (http://gdal.org/gdal_tutorial.html) will show you how to open the tif and read the altitude. Then you use the inverse of the geo transform to convert the pixel row/col to the coordinates in the TIF's SRS. The tutorial will also show you how to get the SRS for the tif.

The TIF SRS may not be geodetic coordinates, or not in the datum you wish. If that is the case, the OGR tutorial (http://gdal.org/gdal_tutorial.html) will show you how to convert coordinates from the TIF's SRS to the one you want (e.g. WGS84).

I cannot stress enough that the tutorials and source code for the GDAL raster utilities are your friend. All that you're asking to do has been implemented in those utilities, which are simple and very well written.

-reilly.

Related Solutions

[GIS] How to read Geotiff tags and pixel per pixel values using GDAL C#

You have two questions:

Reading pixel data from the Geotiff: Here you find a C# GDAL Read Raster Code Sample. The final reading method is called Band.ReadRaster!
Reading Geotiff-Tags: Depends which Tags you mean...
- If you want to read the GeoTransform-Parameters (Georeference-Info), you would do that with the method Dataset.GetGeoTransform.
- If you want to read the Projection-Parameters, you would do that with Dataset.GetProjectionRef.
- If you want to read any other Geotiff Tags, forget GDAL and use any other lib, like LibTiff.Net.

Python GDAL – Extracting Coordinates and Pixel Values from GeoTiff

This should get you going. The raster values are read using rasterio, and pixel centre coordinates are converted to Eastings/Northings using affine, which are then converted to Latitude/Longitude using pyproj. Most arrays have the same shape as the input raster.

import rasterio
import numpy as np
from affine import Affine
from pyproj import Proj, transform

fname = '/path/to/your/raster.tif'

# Read raster
with rasterio.open(fname) as r:
    T0 = r.transform  # upper-left pixel corner affine transform
    p1 = Proj(r.crs)
    A = r.read()  # pixel values

# All rows and columns
cols, rows = np.meshgrid(np.arange(A.shape[2]), np.arange(A.shape[1]))

# Get affine transform for pixel centres
T1 = T0 * Affine.translation(0.5, 0.5)
# Function to convert pixel row/column index (from 0) to easting/northing at centre
rc2en = lambda r, c: (c, r) * T1

# All eastings and northings (there is probably a faster way to do this)
eastings, northings = np.vectorize(rc2en, otypes=[float, float])(rows, cols)

# Project all longitudes, latitudes
p2 = Proj(proj='latlong',datum='WGS84')
longs, lats = transform(p1, p2, eastings, northings)

Best Answer

Related Solutions

[GIS] How to read Geotiff tags and pixel per pixel values using GDAL C#

Python GDAL – Extracting Coordinates and Pixel Values from GeoTiff

Related Question