1. Grid Algebra FE 423 - Lecture 3a

2. 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.

3. Practice Problem 1: Identify the slope of each square

4. Practice Problem 2: Identify the aspect of each square

5. Practice Problem 3: Estimate slope for each cell

6. Practice Problem 4: Estimate aspect for each cell

7. Practice Problem 5: Shade convergent topography

8. Practice Problem 6: Shade convergent topography

9. SCHEDULE

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

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

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

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

14. 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])

15. 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

16. 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

17. HANDLING RESULTS Naming Outputs Finding disc location Other useful stuff

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

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