tissot

Project Tissot indicatrices on axesm-based map

Syntax

h = tissot h = tissot(spec) h = tissot(spec,linetype) h = tissot(linestyle) h = tissot(spec,PropertyName,PropertyValue,...) h = tissot(linetype,PropertyName,PropertyValue,...)

Description

h = tissot plots the default Tissot diagram, as described above, on the current axesm-based map and returns handles for the displayed indicatrices.

h = tissot(spec) allows you to specify plotting parameters of the displayed Tissot diagram as described above.

h = tissot(spec,linetype) and h = tissot(linestyle) specifies the line style and color.

h = tissot(spec,PropertyName,PropertyValue,...) and h = tissot(linetype,PropertyName,PropertyValue,...) allow the specification of any property and value recognized by the line function.

Background

Tissot indicatrices are plotting symbols that are useful for understanding the various distortions of a given map projection. The indicatrices are circles of identical true radius on the Earth's surface. When plotted on a map projection, they indicate whether the projection has certain features. If the plotted indicatrices all enclose the same area, the projection is equal area (for example, a Sinusoidal projection would have this feature). If they all remain circular, then conformality is indicated (a Mercator projection has this property). Distortions in meridional or parallel distance are exhibited by flattened or stretched indicatrices. Many projections will show very even, circular indicatrices in some regions, often near the center, and wildly distorted indicatrices in others, such as near the edges. The Tissot diagram is therefore very useful in analyzing the appropriateness of a projection to a given purpose or region.

The general layout of the Tissot diagram is defined by the specification vector spec.

spec = [Radius]
spec = [Latint,Longint]
spec = [Latint,Longint,Radius]
spec = [Latint,Longint,Radius,Points]

Radius is the small circle radius of each indicatrix circle. If entered, it should be in the same units as the axesm-based map Geoid. The default radius is 1/10th the radius of the sphere.

Latint is the latitude interval between indicatrix circle centers. If entered it should be in the axesm-based map AngleUnits. The default value is one circle every 30º of latitude (that is, 0º, +/-30º, etc.).

Longint is the longitude interval between indicatrix circle centers. If entered it should be in the axesm-based map AngleUnits. The default value is one circle every 30º of latitude (that is, 0º, +/-30º, etc.).

Points is the number of plotting points per circle. The default is 100 points.

Examples

axesm sinusoid; framem
tissot

Tissot diagram for a world map that uses a sinusoidal projection. The indicatrices to the north and south are more distorted than the indicatrices near the equator.

The Sinusoidal projection is equal area.

setm(gca,'MapProjection','Mercator')

Tissot diagram for a world map that uses a Mercator projection. Each indicatrix is a circle. The indicatrices to the north and south are larger than the indicatrices near the equator.

The Mercator projection is conformal.

More About

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Line Style and Color

Specify the line style and color as a character vector or string containing symbols. The symbols can appear in any order. You do not need to specify a color. For example, specify a red dashed line using 'r--'.