Grid Algebra FE Lecture 3a

From Last Week: Use a sun-angle calculator from the web to identify the sun angle for the beginning and end of this class period. Make a hillshaded image of the UW area for these times. Using a DEM of steep topography, map the areas of steep and convergent topography.

Practice Problem 1: Identify the slope of each square

Practice Problem 2: Identify the aspect of each square

Practice Problem 3: Estimate slope for each cell

Practice Problem 4: Estimate aspect for each cell

Practice Problem 5: Shade convergent topography

Practice Problem 6: Shade convergent topography

SCHEDULE

OUTLINE Map Query Reclassify Map Calculator Handling Results Reading/Revising Equation

MAP QUERY grid vs. number([dem] > 500) grid vs. grid([snow] > [melt]) grid vs. equation(([snow]-[melt]) > 10)

RECLASSIFY Beyond just yes/no allows low/medium/high

MAP CALCULATOR Put in any equation SWE z1 =d 1 +d 2 *E z + d 3 *E z 2

OPERATORS ! anotherGrid : Grid % anotherGrid : Grid & anotherGrid : Grid * anotherGrid : Grid + anotherGrid : Grid - anotherGrid : Grid / anotherGrid : Grid < anotherGrid : Grid << anotherGrid : Grid <= anotherGrid : Grid <> anotherGrid : Grid = anotherGrid : Grid > anotherGrid : Grid >= anotherGrid : Grid >> anotherGrid : Grid And anotherGrid : Grid ~ : Grid Negate : Grid Not : Grid Or anotherGrid : Grid XOr anotherGrid : Grid ^ anotherGrid : Grid | anotherGrid : Grid Any unmelted snow? ([snow] > [potential melt]) Total runoff? ([rain] + [melt]) Volumetric soil creep rate? ([soil creep rate] * [soil depth])

Numbers-to-Grids:.AsGrid Numbers must be converted to grids SWE z1 =d 1.AsGrid + d 2.AsGrid*E z + d 3.AsGrid*E z 2

PARSING Our notation is not specific SWE z1 =d 1 +d 2 *E z + d 3 *E z 2 Precedence is what we want SWE z1 =d 1 +(d 2 *E z ) + (d 3 *(E z 2 )) Left-to-right is what ArcView does SWE z1 =(((d 1 +d 2 )*E z ) + d 3 )*E z 2

HANDLING RESULTS Naming Outputs Finding disc location Other useful stuff

READING/REVISING EQUATION What equation did I use? What happens if I change it?

Reading from ArcDoc Spatial modeling –Cell-based Modeling with GRID Functions: locals, focals, and zonals From ArcView Help –Grid (Class)