Geographic Projection Coordinate Convert User Manual

View Projection Coordinate Convert in App Store

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Geographic Projection Coordinate Convert Tool is used to convert coordinate between two projection coodinate systems. Thousands of common projection coordinate systems are built in app. What's more, all projection parameters can be user-defined.

Related Concepts

• Geographic Coordinate Systems(GCS)

GCS

Geographic coordinate systems uses a three-dimensional spherical surface to define locations on the earth. A GCS is often incorrectly called a datum, but a datum is only one part of a GCS. A GCS includes an angular unit of measure, a prime meridian, and a datum (based on a spheroid). A point is referenced by its longitude and latitude values. Longitude and latitude are angles measured from the earth's center to a point on the earth's surface. The angles often are measured in degrees (or in grads). The illustration above shows the world as a globe with longitude and latitude values.

For detail, please visit ArcGIS website What are geographic coordinate systems?

• Projected Coordinate Systems(PCS)

A projected coordinate system is defined on a flat, two-dimensional surface. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. A projected coordinate system is always based on a geographic coordinate system that is based on a sphere or spheroid.

For detail, please visit ArcGIS website What are projected coordinate systems?

• Projection parameters

A map projection by itself isn't enough to define a projected coordinate system. You can state that a dataset is in Transverse Mercator, but that's not enough information. Where is the center of the projection? Was a scale factor used? Without knowing the exact values for the projection parameters, the dataset can't be reprojected. For example, Gauss-Kruger projection need latitude of natural origin, longitude of natural origin parameters and Albers Equal-Area Conic projection need latitude of first standard parallel, latitude of second standard parallel parameters.

For detail, please visit ArcGIS website Projection parameters

Steps

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1. Select a source projection coordinate system

   Tap the button right of λ icon, and select a projection coordinate system from presented table view. It is hard to find what we want in so many PCS, so you'd better type key word in the top search bar.

2. Fill in the source coordinate

   Source coordinate is the 2-D coordinate under PCS selected in step 1. For example, the source coordinate in the figure above show that the unconverted coordinate is (-1.510, 0.694). If you don't want to type word for word, just tap button Select from map and long press to select a point in the map view. App will convert the selected point into coordinate under source PCS automatically.

3. Select a destination projected coordinate system

   Just like step 1. Tap button on the right of the below λ icon to select destination PCS. The destination PCS in the figure is Sphere Mercator.

4. Start the conversion

   Tap Convert button. The result will show in Result table cell immediately.

Projection parameters

The projection parameters are defined in PROJ.4 project. Every projection type has different projection parameters. For example, Albers Equal-Area Conic projection parameter is as followed.

+proj=aea   +lat_1=Latitude of first standard parallel
            +lat_2=Latitude of second standard parallel
            +lat_0=Latitude of false origin 
            +lon_0=Longitude of false origin
            +x_0=Easting of false origin
            +y_0=Northing of false origin

Some of these can be found in the GeoTIFF Projections Transform List