HOW TO MAKE A TOPOGRAPHIC MAP USING SKETCHUP

Modelling and analyzing topographic map becomes more convenient with the aid of modern technology such as online map surveying and 3-D modelling software.

Most contour lines found in online topographic maps such as Google map (https://www.google.com.ph/maps), Open Street Maps (https://www.openstreetmap.org/), NAMRIA (http://www.namria.gov.ph/), etc. are labelled with elevations. These topographic elevations found mostly on online map can only be examined in a macro scale level, showing a minimum of 20 meter contour interval.

Topographic maps may have many contour lines. The contour interval chosen for a map depends on topography in the mapped area. In areas with high relief the contour interval is usually larger to prevent the map from having too many contour lines. On the other hand, areas with moderate slope required an enormous number of contour lines in order to show such great detail.

Technically, contour lines can be drawn for any elevation. Using different 3-D modelling software such as SketchUp, we can expand the contour interval, producing many contour lines. This process of expanding the contour interval is applicable in small areas with moderate slope topography.

In this tutorial, we will learn how to draw contour lines and expand the contour intervals using SketchUp. Here, we will try to adjust the value of contour interval from 20 meter to 5 meter.

Before we start the modelling procedures, we should analyze first the contour interval of the topographic map. Here’s a quick guide on how to read topographic map.

QUICK GUIDE ON HOW TO READ TOPOGRAPHIC MAP 

(1) Index Contour, (2) Minor Contour Line, (3) Contour Interval

To determine the contour interval of a point, you must have a reference line from which to start. This reference line is an index contour (major contour line). Based on the reference map, an index is one that is bolder, darker contour line and has a value written on the line. The value written on the index line is the elevation. 

Every topographic map has a contour interval which remains constant throughout the drawing. The elevation value of the minor contour lines can be determined through the counting process from one index contour to another. For instance, if the first index contour line has a value of 100m and the second index contour line has a value of 200m, the value of the minor contour lines will be 120m, 140m, 160m, and 180m. Therefore, the contour interval is 20 meter.

20 Meter Contour Interval

6 CARDINAL RULES OF CONTOURS

RULE #1: Contour always occur in pairs

RULE #2: Contours never cross

RULE #3: Contours have equal vertical separation

RULE #4: All contour lines close in themselves

RULE #5: Contours do not merge

RULE #6: The steepest slope is a line perpendicular to the contour

A. HOW TO VIEW GOOGLE MAP WITH CONTOUR LINES

STEP 1: Open the Google map> Click the expand side panel>search the location of the site by typing the address on the search bar> click the 'map view'. In the figure, you see the results for Angono-Binangonan Petroglyphs.

STEP 2: Click the menu from the Google map panel> click the terrain option

STEP 3: Use the Zoom controls on the left corner and click the negative sign to zoom out the map. Make sure that all contour lines are visible when zoom out> click 'print screen' (keyboard)> paste the image in 'paint'> save in JPEG format.

B. HOW TO CREATE A 3-D TOPOGRAPHIC MODEL USING SKETCH-UP

STEP 1: Click 'File'> import image> select the map image> click 'Open'

STEP 2: Draw a 500 meter line. Here, click the 'lines' from the drawing tool> type the 500 meter value on the 'Edges length' located in the 'Entity Info' then press Enter. The 500 meter line will serves as a scale reference. Re-scale the imported topographic map image (make sure the 500 meter graphic map scale image will fit into the the 500 meter line.

STEP 3: Draw a 1000 x 1000 meter border line box

STEP 4: To draw curves, click the 'Arcs' from the drawing tool> Trace the contour lines from the map> delete any faces that formed when lines were drawn

ELEVATION VALUE

STEP 5: To adjust the elevation of each contour lines, use the Move Tool. Click the contour line that you want to adjust, then click the Move Tool> press the up key button (keyboard)> pull-up the selected contour line or object vertically (it is locked to the blue axis)> Type the elevation value shown in 'Measurements Toolbar' (follow the elevation value from the Google map)> press Enter key.

STEP 6: Ctrl+A (Select all). Using the Sandbox Tool, click the icon ‘From Contours’ or go to Draw>Sandbox>From Contours.  This process will automatically generate 3D object(s).

RESULT : 3-D Topographic model with 20 meter contour interval

C. HOW TO CREATE A 5 METER CONTOUR MAP USING SKETCH- UP

Here, we will try to adjust the contour interval of our 3-D model terrain from 20 meter (Google map contour reference) to 5 meter contour interval.

STEP 1: Lock the grouped terrain model and the grouped index contour lines. To do that, select the model> right click> click 'Lock'

STEP 2: Draw a square or rectangular plane> make group> move the plane to the lowest point of the terrain

Square plane

STEP 3a: Make a multiple copies of the plane until the whole terrain model is covered. To do that, select the plane then click the Move Tool + Ctrl key> press the up key button (from the keyboard)> pull-up the selected plane vertically (it is locked to the blue axis)> Type the elevation value in the Measurements Toolbar (in this case, type 5 meter in the Measurements Toolbar) and press the Enter key.

STEP 3b: Type 50x (to duplicate the plane)> press Enter

STEP 4: Select the entire plane> Right click > make group> Hide

STEP 5: Unlock the terrain model. To do that, select the model> right click> click Unlock.

STEP 6: Explode the terrain model. To do that, select the model> right click> click Explode

Exploded Model

STEP 7: Unhide the grouped plane. To do that, go to Edit> select 'unhide'> click ‘Last’

STEP 8: Select the grouped slicing planes> Right click> choose ‘Intersect Faces’> click ‘With Model.’ This process will enable you to intersect your grouped slicing planes with your terrain model.

STEP 9: Delete or Hide the grouped slicing planes.

Result so far

STEP 10: Based on the “6 Cardinal Rules of Contours”, all contours never cross or merge with each other. Thus, we need to remove all the overlapping edges from the model. To do that, hold Ctrl+ while applying the Erase Tool. Remove all the overlapping edges.

SUMMARY

FINAL OUTPUT

FINAL OUTPUT

Finally, you have a topographic map with 5 meter contour interval. You can now start designing the site by adding different structural elements such as path walk, roads, garden, buildings, house etc. Label all the contour lines using Sketch Up Layout.