Why scaleruler and northarrow functions cannot be used in mapshow figures

Hello everyone,

I just want to simply show scalebar and northarrow on my maps using the scaleruler and northarrow functions.

I tried the official help codes of MATLAB R2022a on mapshow as follows:

figure
mapshow boston.tif
S = shaperead('boston_roads.shp');
surveyFeetPerMeter = unitsratio('sf','meter');
x = surveyFeetPerMeter * [S.X];
y = surveyFeetPerMeter * [S.Y];
mapshow(x,y)
scaleruler on
northarrow

Then, I got the following errors:

Could you please tell me why and how to use scaleruler and northarrow on a mapshow figure?

Thanks a lot.

Answer 1

[Walter Roberson]

When there is no existing axes then mapshow creates a standard numeric axes. mapshow is for displaying maps without projection, which is done on standard axes.

If, however, the existing axes is a mapping axes then mapshow can draw on it, but you need to avoid changing the map properties.

So you could axesm() mapshow() scaleruler... but you should consider using a function to display the map in a map axes instead of mapshow

[Songqiu]

Dear Walter,

Thank you very much for your answer.

Actually scaleruler and northarrow functions work well with geoshow(), but my dataset has a local projected coordinate system, so I hope to use the mayshow function to draw the images and vector files.

I could not understand [... but you should consider using a function to display the map in a map axes instead of mapshow] so much yet.

Could you please show me a simply example to display the scalebar and northarrow based on your idea? or tell me how to show the data having a local projected coordinate system with a scalebar?

Thanks a lot.

[Walter Roberson]

The below needs some work, obviously, but shows how you can create an axesm first, after which you can mapshow() and scaleruler() and northarrow.

figure
axesm('MapProjection', 'lambert');
mapshow boston.tif
S = shaperead('boston_roads.shp');
surveyFeetPerMeter = unitsratio('sf','meter');
x = surveyFeetPerMeter * [S.X];
y = surveyFeetPerMeter * [S.Y];
mapshow(x,y)
scaleruler on
northarrow

[Songqiu]

Dear Walter,

Thank you very much for your answer.

I have a polygon vector dataset with a local Projected Coordinate System: JGD_2011_Japan_Zone_8 (EPSG code 6676). And I wrote the following codes to generate a figure:

load('D:\Rinsouzu\Test.mat', 'ClassName', 'ClassCode')
PC = readgeotable('D:\Rinsouzu\Takapyou1\CHM25cmOk_TreeCrown_2C_Rinsou.shp');
uID = unique(PC.RinsouCode);
uID = uID(uID > 0);
ListClass = {'y', 'c', 'r', 'b', 'm', 'k'};
Temp = cell(numel(uID), 1);
N = 1;
Fig = figure;
% ax = axesm('MapProjection', 'tranmerc');
for i = 1 : numel(uID)
    Temp{i} = ClassName(ClassCode == uID(i));
    Idx = PC.RinsouCode == uID(i);
    if Temp{i} == "Akamatsu"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{1}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Hinoki"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{2}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Karamatsu"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{3}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Kouyoujyu"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{4}, 'FaceAlpha', 1);
        N = N + 1;
    elseif Temp{i} == "Sugi"
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{5}, 'FaceAlpha', 1);
        N = N + 1;
    else
        h(N) = mapshow(PC(Idx, :), 'FaceColor', ListClass{6}, 'FaceAlpha', 1);
        N = N + 1;
    end
end
lgd = legend(h, Temp, 'Location', 'northeastoutside');
title(lgd, 'Legend')
box on
grid on
grid minor

Then, I got the following result that I want:

When I turn on the line: [ax = axesm('MapProjection', 'tranmerc');] that you told me, eventhough the codes can run normally, I lost the axis labels and grid lines as follows:

If I continue to run the following codes to add a scalebar and northarrow, I got the following bad result and error:

%%
scaleruler on
scaleruler('units', 'meter');
setm(handlem("scaleruler"), "XLoc", 1700, "YLoc", 91100, "MajorTick", 0 : 20 : 100, "FontSize", 8)
northarrow

My purpose is very simply that is to add a scalebar and a northarrow on the first map of the above figures.

Could you please have a look at my codes and tell me how to improve it for my purpose?

Thanks a lot.

[Walter Roberson]

Unfortunately I do not have your .mat or the .shp file, and when I test the setm() works for me.

However I would remind you that the documentation for mapshow says (Tips)

• You can use mapshow to display vector data in an axesm figure. However, you should not subsequently change the map projection using setm.

I suspect that setting XLoc and YLoc counts as changing the projection (but I am not sure.)

It looks to me as if you have a scale problem affecting the rulers -- I would guess a scale factor of 1000 problem.

[Songqiu]

Dear Walter,

Please find the attached zip file which includes all files for my code.

Please have a test for it.

Thanks a lot.

[Walter Roberson]

scaleruler on
scaleruler('units', 'meter');

That is creating two scale rulers, one on the first call and one on the second call. Then handlem() is retrieving both of them, and setm() is giving an error because setm() is giving an error because it expects a scalar.

Remove the first of the calls to remove the error message.

[Songqiu]

Dear Walter,

Thank you very much for your reply.

Although the error did not come up anymore, I got the following bad results that are not I want.

The second one is that of adding [axis manual] after grid minor.

I do not find the scalebar and northarrow in the figure area, but find two additional items in the legend.

scaleruler and northarrow are difficult to use.

Thank you very much again for your patient answers.