Surface Analysis of spatial analysis

We can use the "surface analysis (Surface)" tool to quantify and visualize the topography of the landscape.

slope Direction (Aspect): Gets the slope direction of the grid surface. It is found that the maximum change rate of each image element to the direction of its adjacent pixels is the downhill direction.

Isoline (Contour): A line element class that creates an isoline (contour map) on a grid surface.

Contour sequence (contour List): an element class that creates a selected contour value from a grid surface.

an isoline with a barrier (contour with barriers): An isoline is created from the grid surface. If a barrier element is included, an isoline is allowed to be generated independently on both sides of the barrier.

curvature (curvature): calculates the curvature of the grid surface, including the section curvature and the plane curvature.

Fill in the Cut fill: Calculate the volume change between the two surfaces. Typically used to perform filling operations.

Mountain Shadow (hillshade): Create relief shading According to the surface grid by considering the angle and shadow of the illumination source.

Viewpoint Analysis (Observer point): identify the observed points visible from the position of each grid surface.

gradient (Slope): A determination of the slope (the maximum rate of change in gradients or Z values) in the pixels of a grid surface.

Sight (viewshed): determines the position of the grid surface that is visible to a set of observation point elements.

The following categories look at these tools:

a variety of contour lines tools

1 Contour Line (contour)

Based on raster surface data, contour line element classes are created. You can specify the starting line and interval.

2 Isoline list (contour)

The element class that creates the specified contour value based on the grid surface.

3 contour lines with obstacles (contour with barriers)

Create contours from the grid surface. If a barrier element is included, an isoline is allowed to be generated independently on both sides of the barrier.

TIPS: On the quality of contours

In rare cases, the contour of the created contour may be square or uneven, looking like a boundary along a grid element. This may occur because the values of each grid are integers and fall exactly on the isoline. This is not a problem, but the contour is merely rendering the data as it is.

If you want the contours to be smoother, a viable approach involves smoothing the source data or adjusting the starting contour.

second, surface characteristics related tools

1) Slope direction (Aspect)

This tool obtains the maximum rate of descent in the Z-value of each image element to its adjacent pixels direction.

Conceptually, the ramp tool will fit a plane according to the z value of a 3 x 3 pixels around the pixels or center pixels to be processed. The orientation of the plane is the slope of the image to be processed.

The output grid value will be the compass direction of the slope. The slope is indicated by a positive degree between 0 and 359.9 degrees, and the north is measured clockwise from the datum direction. The level of the input grid (with 0 gradient) pixels is allocated-1 slope.

2) slope (Slope)

The gradient refers to the maximum change rate of Z value in each image element.

Conceptually, the tool fits a plane with the z-value of a 3 x 3 pixels around the pixels or center pixels to be processed. The slope value of the plane is calculated by the maximum mean method.

If the z-value of a pixels position in a neighborhood is NoData, the z-value of the center image element is assigned to that position. If the center pixels in the direct neighborhood (3 x 3 window) are NoData, the output will be NoData.

Determine the measurement unit (degree or percentage) of the output gradient data.

degree-slope inclination, Unit: degree, Range: 0 ~ 90.

percent_rise-elevation increment percentage, also known as percentage slope, range: 0 ~∞.

The tool can be used in conjunction with other types of continuous data, such as the population, to identify sharp changes in values.

Detailed algorithm for tools: Http://help.arcgis.com/zh-cn/arcgisdesktop/10.0/help/index.html#/na/009z000000vz000000/

3) curvature (curvature)

The main output result is the surface curvature of each image element. The curvature is the second derivative of the surface, or it may be called the slope slope. The curvature indicates that the surface of the image element is convex upward. A negative curvature indicates that the surface openings of the pixels are concave upward. A value of 0 indicates that the surface is flat.

The output curvature types available for selection are: section curvature (slope along the maximum slope) and plane curvature (perpendicular to the direction of the maximum gradient).

From the point of view of application, the output of the tool can be used to describe the physical characteristics of Basin basin, so as to facilitate understanding of erosion process and runoff formation process. The gradient affects the overall movement rate at downhill. The slope will determine the direction of flow. The curvature of the profile will affect the acceleration and deceleration of the flow, which in turn will affect erosion and deposition. The plane curvature affects the flow convergence and dispersion.

Three, fill in the excavation (cut fill)

Calculate the volume change between the two surfaces. Typically used to perform filling operations.

By default, a dedicated renderer is used to highlight the location where the fill operation is performed. The renderer draws the area of the dug into blue and the filled area is painted red. Areas that do not change will appear dimmed.

Four, the Mountain Shadow (Hillshade)

The main factor to consider in this tool is the position of the sun (illumination source) in the sky. Look at the parameter settings for this tool:

The azimuth angle (Azimuth) refers to the angle direction of the sun, which is measured clockwise in the range of 0-360 degrees to the north as the datum direction. The azimuth angle of 90º is east.

The default orientation angle for this tool is 315º (NW).

height (altitude) refers to the angle or slope of the sun above the horizon. The height of the unit is degrees, the range is 0 (on the horizon) to 90 (located on the head) between.

The default value for this tool is 45 degrees.

Model sahdows

By selecting Model sahdows, we can calculate the local illumination degree and whether the pixels fall into the shadow. The shadow value is 0, and all other pixels are encoded as integers between 1 and 255.

Z-factor (z Factor)

Z-units are not the same as the x,y units of the input surface, and Z-Factor can be used to adjust the unit of measurement for z units. When the final output surface is computed, the Z-factor is multiplied by the z-value of the input surface.

If the x,y unit and Z unit are in the same unit of measurement, the z factor is 1. This is the default value. In addition, Z-Factor can also be used for terrain exaggeration.

For example, if z units are feet and x,y units are meters, you should use Z factor 0.3048 to convert Z units from feet to meters (1 feet = 0.3048 meters).

Detailed algorithm for tools: Http://help.arcgis.com/zh-cn/arcgisdesktop/10.0/help/index.html#/na/009z000000z2000000/

v. Visibility Analysis

1) Viewpoint Analysis

The Viewpoint tool generates binary coded information about which positions can be seen at the point of observation. The observation point is limited to a maximum of 16. This tool only supports point element input.

The visibility information is stored in the VALUE item. If you want to display all the grid areas that you see through View 3, open the output Grid property sheet, and then select the records that point 3 (OBS3) equals 1 and all other viewpoints equal to 0.

For example, the following is a property sheet for the results of the visual analysis of 7 observation points:

2) Visual field

The visual field tool creates a raster data that records the number of times each area can be seen from the input or view line element position. The value is recorded in the value item of the output grid table.

TIPS: Controlling visibility analysis

You can limit the area of a grid that is checked by specifying different items in the feature attribute data set. There are nine items: SPOT, Offseta, Offsetb, AZIMUTH1, AZIMUTH2, VERT1, VERT2, RADIUS1 and RADIUS2.

The drawings help to understand:

Default values for these values:

Options	Default value	Parameter meaning
SPOT	Using bilinear interpolation to estimate	Elevation of the position of the observation point
Offseta	1	High observation point (for example, instrument height), must be positive
Offsetb	0	Each image element is high (for example, the target is high) and must be positive
AZIMUTH1	0	Initial azimuth angle of observation
AZIMUTH2	360	Observation of the end azimuth angle
VERT1	90	Observe the initial vertical angle
VERT2	-90	Observe the end of the vertical angle
RADIUS1	0	Starting visible radius
RADIUS2	Infinity	Terminate visible radius

If the view factor dataset is a point element class, each observation point can have a unique set of observation constraints in the property sheet. If the view factor dataset is a Polyline feature class, then each fold along the input polyline uses the same observation constraint contained in the line records of the property sheet. If an item does not exist, the default value is used.

o, the tool for surface analysis, summed up to this end.