[GIS] Converting resolution in degrees to resolution in meters

coordinate systemrasterwgs84

I have a raster data with spatial reference GCS-WGS-1984 (datum D-WGS-1984). Its cell size is mentioned as (0.00045, 0.00045) in degrees.

How can I convert this resolution in meters (i.e. linear unit)?

Best Answer

Easiest way is to convert the raster to a projected system, and get the cell size directly in meters.

That not being possible, or desirable, you can still convert lat/lon values to metric values, but you'll run into an accuracy problem. This is because, 1º of distance represents different values in metric units depending on your location and bearing (0.00045º is about 50m around the Equator, but about 30m around London). There are ways to calculate it, but you'll be generalizing somewhat your results.

If accuracy is not very important and you only want an overall idea of the cell size, you can either do it with the Haversine formula (easier but less precise) or Vincenty's inverse formula (more precise, but way more complicated).

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[GIS] Converting shapefile in NAD27 from meters to decimal degrees to match xy data

You could try to Project to this geographic coordinate system.

Coordinate System>Geographic Coordinate System>North America>NAD 27.prj

GCS_North_American_1927

Angular Unit: Degree (0.017453292519943295) Prime Meridian: Greenwich (0.000000000000000000) Datum: D_North_American_1927 Spheroid: Clarke_1866 Semimajor Axis: 6378206.400000000400000000 Semiminor Axis: 6356583.799998980900000000 Inverse Flattening: 294.978698200000000000

[GIS] How to figure out the length of polyline features in a feature class with a WGS 1984 coordinate system

I thought at first the arcpy.Polyline.getLength() method would work, as you can specify a measurement type and units but it did not because it is GCS. As you can see here, we are still in Decimal Degrees:

>>> with arcpy.da.SearchCursor("line_wgs", 'SHAPE@') as rows:
...     for row in rows:
...         print row[0].getLength('PLANAR', 'METERS')
...         
0.00193201661559
>>> desc = arcpy.Describe("line_wgs")
>>> desc.spatialReference.factoryCode
4326

What you can do is add a spatial reference to your search cursor (such as the Web Mercator):

>>> with arcpy.da.SearchCursor("line_wgs", 'SHAPE@', spatial_reference=arcpy.SpatialReference(102100)) as rows:
...     for row in rows:
...         print row[0].getLength('PLANAR', 'METERS')
...         
215.071313581
>>>

Note, since WGS Web Mercator is in meters you can just use the length property as you did in your first one:

>>> with arcpy.da.SearchCursor("line_wgs", 'SHAPE@', spatial_reference=arcpy.SpatialReference(102100)) as rows:
...     for row in rows:
...         print row[0].length
...         
215.071313581
>>>

Best Answer

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[GIS] Converting shapefile in NAD27 from meters to decimal degrees to match xy data

[GIS] How to figure out the length of polyline features in a feature class with a WGS 1984 coordinate system

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